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BEFRIGESATION TRAINING
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Sheets - Student
Refrigeration, Air Conditioning, and Heating

Refrigeration
Trai ning System
Job Sheets;rs,tudent
REFRIGERATION, AIR CONDITIONING, AND HEATING

REFRIGERATION
TRAINING SYSTEM

by
the Staff
of
Lab-Volt Ltd.

Copyright @ 2008 Lab-Volt Ltd.

All rights reserved. No part ofthis publication may be reproduced,

in any form or by any means, without the prior written permission
of Lab-Volt Ltd.

Legal Deposit - Second Trimester 2008

rsBN 978-2-89640-278-6
2€9640-051-6 (1"t Edition, 2006)

SECOND EDITION, MAY 2OO8

Printed in Canada
May 2008
 Foreword

The Lab-Volt Refrigeration Training System, Model 3431, provides the student with
theoretical and practical knowledge in the operation and maintenance of typical
refrigeration components and systems. Practicalexperience is gained bythe student
through procedure steps contained in each job sheet.

The courseware starts by introducing the student to the fundamentals of physics

related to refrigeration. Then the basic refrigeration cycle is studied. Next typical
refrigeration components are studied. The student is then familiarized with system
startup, inspection, and troubleshooting.

The topics covered in this manualare provided in the form of job sheets. Each job
sheet includes a brief description of the task to perform, drawing(s) related to this
task when necessary, as well as a step-by-step procedure of the task.

To obtain further information about the covered topics, you can ask your instructor
or refer to the reference textbooks listed in the Appendix section.

The Refrigeration Training System is intended for use with the Heat, Ventilating, and
Air Conditioning (LVHVAC) software, Model 36973, a powerful learning tool that
allows the real{ime monitoring of the temperature and pressure sensed at the critical
points of the system. The software automatically calculates and refreshes the system
variables, including the refrigeration capacity, the coefficient of performance, and the
superheat. Moreover, a plotting function displays in real-time the pressure-enthalpy
diagram, constantly changing as the refrigeration cycle evolves toward equilibrium.
Furthermore, a trend recorder provides a graph over time of the data acquired on the
pressure, temperature, and compressor.

ln order for students to be able to perform the job sheets in this manual, therefore,
the LVHVAC software must have been previously installed on the student's
computer. The material covered in this manual is intended to provide a level of
refrigeration knowledge that will enable the student to enter more specialized areas
of study in this field. The answers to all procedural questions in this student manual
can be found in the Lab-Volt lnstructor Guide (part number 37869-3).

ilt
 Table of Contents

lntroduction . ... vil

Job Sheet 1 SystemOverview ...1-1

of the components on the Refrigeration Training
ldentification
Sysfem. Familiarization with the LVHVAC software. Filling out an
lnspection Report.

Job Sheet 2 RefrigerationFundamentals. .....2-1

Thermal energy and its transfer. Basic principles of refrigeration.
The refrigeration cycle. Pressure and temperature measurements.
Refri g e ra nt. R 1 34a te m pe ratu re- p re s s u re re I ati o n s h ip.

Job Sheet 3 RefrigerationComponents(Partl) .... ... 3-1

The compressor and its charactersfics: volumetric flow rate,

volumetric efficiency, compression ratio. The liquid receiver. The
filter/drier. The moisture/liquid indicator. The suction line
accumulator.

Job Sheet 4 Refrigeration Components (Part ll) and

EnthalpyDiagram ...4-1
The condenser. Expansion (metering) devices: capillary tubes and
thermostatic expansion valves. The evaporator. Enthalpy tables.
Pressure-enthalpy diagrams. Measuring the net refrigeration effect
(NER), the heat of compression, and the coefficient of performance
of the training system, based on the graphical representation of its
refrigeration cycle displayed by the software.

Job Sheet 5 ElectricalControlofRefrigerationSystems ... .. 5-1

Basic electricity. Ohm's law. Electrical Power. Types of electric

current. C/osed and open circuits. Measuring voltage, resistance,
and current Series and parallel circuits. Safety rules. Measuring
thermostat continuity. Measuring the individual resistance of the
main components of the training sysfem, and the voltage drop
across these components.

Job Sheet 6 Pressure and Temperature Gontrol in

RefrigerationSystems .....6-1
The conventionalhigh- and low-pressure controllers. The electronic
pressure controller of the training sysfem. Thermostats. Solenoid
valves. Studying the operation of the training sysfem's pressure
controller. Studying the operation and interaction of the training
sysfem's thermostat and solenoid valve.
 Table of Contents (cont'd)

JobSheetT Thermostatic Expansion Valve Adjustment ...... .....7-1

Definition of superheat and subcooling. How to adjust the
thermostatic expansion valve of a refigeration system. Tuning the
valve to obtain an adequate superheat. Observing the effect that a
change in the adjustment of the training system's valve has on the
superheat.

Learning an efficient method for locating faults in a refrigeration

system. Location of instructor-insefted faults in the electricalcontrol
section of the Refrigeration Training System.

Appendices A Technical Data on the Refrigeration Training System

B Unit Conversion Table
C Temperature Scales
D Enthalpy Table for the R-l34a Refrigerant
E Pressure/Enthalpy Diagram for R-l34a Refrigerant
F Reference Textbooks
G Post-Test

We Value Your Opinion!

 Introduction

Refrigeration systems are used for air conditioning, beverage cooling, and freezing
of food. One of the most important applications of these systems is the refrigerator
used for the preservation of food.

Most foods spoil rapidly when kept at room temperature due to the rapid growth of
bacteria. ln many countries, herbs and spices have been traditionally used for
centuries to preserve foods. Another way of preserving foods is by keeping them at
a temperature of around 4.4"C (40"F), which slows down the groMh of bacteria.
Consequently, food kept at this temperature will last much longer.

ln Europe and North America, refrigeration first became important commercially in

the l Bth century: blocks of ice from frozen lakes and ponds were stored in insulated
metal boxes or storerooms for summer use.

lce was first made artificially about in 1820 as an experiment but did not become
commercially practical until 1834. lt was not until 1918 that Kelvinator produced the
fi rst automatic refri gerator.

vll
 SYSIEM OVERVIEW

SYSTEM OVERVIEW

The Lab-Volt Refrigeration Training System consists ofrefrigeration components, as

wellas instrumentation and control components. These components are located on
the front paneland at the rear bottom of the trainer, as Figures 1-1 and 1-2 show. (ln
Figure 1-2, the protecting plate along the mountang base of the
compressor/condenser assembly is not shown).

. The refrigeration components include a compressor, a condenser, expansion

devices (capillaries and a thermostatic expansion valve), an evaporator, and
refrigerant copper tubing.

. The instrumentation and control components permit the electrical control,

monitoring, and protection of the refrigeration components. They include high-
and low-pressure gauges, a lhermostat, a solenoid valve, as well as pressure and
temperature lransmitters. An electronic pressure controller keepsthe compressor
operating at proper levels.

ln addition, an electrical control panel, located at the bottom of the trainer front
panel, provides electrical switches and control knobs to set the system under
various configurations. Silk-screened on the righlhand side of this panel is a
diagram that shows the electrical connections between the system components
requiring an AC voltage to operate. Banana.jacks permit the measurement of this
voltage at various points of the system for maintenance and troubleshooting
purposes.

The Refrigeration Training System is intended for use with the Heat, Ventilating, and
Air Conditioning (LVHVAC) software, which permits the real{ime monitoring of lhe
system variables. This requires that the computer used to run LVHVAC be
connected to the Refrigeration Training System, via a USB connection.
SYSTEM OVERVIEW

Figure 1-1. Front view of the Refrigeration Training System.

CIRGLED CIRCLED
COMPONENT COMPONENT
NUMBER NUMBER
1 Solenoid valve 10 Low (LP)- and high (HP)-pressure gauqes
2 Filter/drier 11 Pressure controller
3 Liquid indicator 12 Main POWER switch
4 Water collectinq trav 13 COMPRESSOR switch
5 Two-way hand-operated valves 14 EVAPOMTOR-FAN SPEED control knob with
on/off switch
6 Expansion (metering) devices 15 CONDENSER-FAN SPEED control knob with on/off
switch
7 Evaporator and its fan 16 HEAT LOAD switch
8 Cooling chamber 17 Electrical diagram with banana jacks
I Remote bulb thermostat 18 USB port
19 Faults access panel

Table 1-1 . Components located on the front panel (ref. to Figure 1-,1).
 SYSTEM OVERVIEW

Figure1.2'ViewoftherearbottomoftheRefrigerationTrainingSystem.

CIRCLED NUMBER COMPONENT

20 Suction line accumulator

21 High-pressure controller with manually-reset breaker

22 Refrigerant receiver

23 Compressor

24 Forced-air condenser

(ref' to Figure -2)'

Table .l -2. components located at the rear bottom of the trainer
1

REFRIGEr.',J7o/n{rF'// Gs
SYSIEM OVERVIEW

Technical Data

Table 1-3 provides technical data on the Refrigeration Training System, at 120 VAC
and 2201240 VAC. This table is also provided as a reference in Appendix A of the
manual.

COMPONENT TECHNICAL DATA

120 VAC 2201240 V AC

Compressor Hermetic-type, 124 W Hermetic-type, 186 W

(0.'167 hp), start (0.2s0 hp), sta(
capacitor, thermally capacitor, thermally
protected, 1 15 VAC, protected,
60 Hz, 18-A locked- 2001240 VAC, 50 Hz,
rotor current (LRA), 12.3-A locked-rotor
2.9-A rated load current (LRA), 2.3-A
current (RLA) rated load curent (RLA)
Refrigerant R-134a R-134a
Nominal charge 1.09 kg (2.4 lb) 1.09 kg (2.4 lb)
oit Polyol esther Polyol esther
Evaporator Forced-air coil with Forced-air coil with
yariable-speed fan, variable-speed fan,
enclosed in a cooling enclosed in a cooling
chamber, 120 VAC, chamber, 240 V,
60 Hz, 0.58 A 50/60 Hz, 0.35 A
Condenser Forced-air coil with Forced-air coil with
variable-speed fan, variable-speed fan,
120 VAC, 60 Hz, 230 VAC, 50/60 Hz,
0.41 A 0.2 A
Thermostat setpoint (typicat) 5"C (41'F) 5'C (41'F)
Pressure conlroller Cut-in 2.07 barg (30 psig) (1)
2.07 barg (30 psig) (1)
settings (typicat) pressure
(cr1)

Delay (ASd) Null Null

Cut-out 0.69 barg ('10 psig) (1)

0.69 barg (10 psig) (rt
pressure (CO'1)

Operating Lower point 1.4 barg (20 psig) (r)

1.4 barg (20 psig) (r)
pressures (typical)

Highest point 7.6 barg (1'10 pstg; t1t

7.6 barg (110 psig) (1)

1 bar gauge (barg) = 1OO kpa gauge = 14.S psa gauge (psig)

Table 1-3. Technicaldata on the Ref.igeration Training System.

 svsTEM ovERvtEw

OBJECTIVE

ln thisJob, you will identifythe main components of the system. You willthen run the
LVHVAC software and record data on the system components in an inspection
report.

EOUIPMENT REQUIRED

Lab-Volt Refrigeration Training System, Model 3431

PROCEDURE

Components ldentification

n 1. Figure 1-3 shows a functional diagram of the Refrigeration Training System.

Fill in the lines below by identifying each ofthe components pointed bythe
arrows in Figure 1-3.

a. s.

b. h.

c. i.

d. j.

e. k.

f.
 SYSTEM OVERVIEW

-D
23.4 aC ry
eb
23.4 0C

@bar
-0.9 g

@
f barg
-4.

6
@
27.4
24.3 "C
"C
I

f vTITF-r

Figure l-3. ldentifying the system components.

Recording System Data in an lnspection Report

! 2. On the control panel of the Refrigeration Training System, make sure the
main POWER switch is set to OFF (O).

Connect the Refrigeration Training System to the computer used lo run the
LVHVAC software, via a USB cable. Turn on the computer and then run the
LVHVAC software.
 SYSTEM OVERVIEW

tr 3. When the software opens, the Refrigeration Diagram of the system is

displayed, showing the main components of the system, as well as the
location of the thermocouple and pressure transmitters along the system,
as Figure 1-4 shows.

File vicw Todt @ @W

fl)q@. 6a g ooooo ffi
ncfiir;erctio uago RdriJq*lon Tr.ffisyim +x
I E
RcfrlGrat Trpc R-13,t

L*Pr6ilc Coatrolcr
sctrotnt (brg) 0

TcrrpGGtu! Contsdr.
sct!#(6C) 0

Evrydd
{;I
Fm Soatd
,PFF
-=
aD@ ED cqd6s
-i r'.rt il I 'a
.i:r 2.r I 'C

T rn SOcd

elD T Hc* Lod

Pffi

t @
-0.9 rarg

rl @c.rg
\:/ -4.J
II
I2
r3
T{
I5
r
72,$
(.[)

?3,?7
2X.8
23,40

(r/ superheBt (.a)

Y fompresaion Ratio
Net Refriqet.tlon Effect (k]/ko)
Idf,al work of Compresrim (kl,&q)

L FloP Rate of Refrig.rant (kglr)

Rdriqeration Capmity (kW)
f oelfrcier* of Pcrtornr.n(e
ail
2r l "a
Rate ofHeat Reitrtiotr !t thc tondcnter (kw)
Vol, flow Rate of Refrig. 6t the €v!p' (}rtlet (tnt/rin)
Retris. Effact Lots bl, Work o, the Exp. Devi(e (kl,/kg)

ooo
rr A0 tr.0 I !,.,
@
) 2.9 ',a

Figure 1.4. Refrigeration Diagram of the LVHVAC software.

ln the diagram, observe that test points T'1 through T7 all provide a proper
temperature reading, which approximately corresponds to the room
temperature. This occurs because the associated temperature transmitters
are currently powered via the USB cable between the Training System and
the computer.

However, note that test points PS1 through PS3 provide non-significant
pressure readings. This occurs because the associated pressure
transmitters are powered only when the Refrigeration Training System is
turned on (via a built-in internal source).

R EFRI G ERATI O N T RAI N I NG SYSTEM

SYSTEM OVERVIEW

n 4. On the Refrigeration Training System, make the following settings:

COMPRESSOR switch . . . ..
OFF(O)
EVAPORATOR-FAN SPEED contiof XnoU . . . 5166 tsee rorei
CONDENSER-FAN SPEED control knob . . . . Half of H|GH
HEAT LOAD switch .. .....
OFF(O)
Thermostal setpoint . ....5"C(41'F)
Manually-operated valves
V1 ..... . Open (handle turned fully counterclockwise)
V2 ..... ......
Closed (handle turned fully clockwise)
V3 ..... . . . . . . Closed (handle turned fully clockwise)

Nolei Take care not lo tum this knob fully counterclockwise, which
would close the knob switch and cause the fan to stay turned off.

!5. Turn on the Refrigeration Training System by setting its POWER switch to
oN (r).

tr6. ln the Refrigeration Diagram ofthe LVHVAC software, observe that there
is no pressure differential across the compressor, since test points pS2
(LP compressor side)and PS1 (HP compressor side) indicate approximatety
the same pressure. Also, observe that the compressor voltage and current,
as indicated by test points V and A below the compressor icon, are both null
(0 V and 0.0 A, respeclively), indicating that the compressor is off.

n7. Fill in the blank fields of the first two sections of the inspection report
(Table 14): IDENTIFICATION, and SYSTEM |NFORMAT|ON.

Then, fill in the field ldle Pressures and Temperature of the section
OPERATIONAL INFORMATION, based on the pressures and temperature
indicated at test points PS2, PS1, and T6 of the Refrigeration Oiagram in
the LVHVAC software.

Note: Some,Telds of Table 1-4 are filled with diagonal tines to

indicate that you need not fill in them for now. This occurs
because the theory related to these parameters will be seen in
the job sheets to follow. You willcomplete the repoft at the end of
Job Sheet 7.

tr 8. Turn on the system compressor by setting the COMpRESSOR switch to the

ON (l) position.

. Note that this causes one of the two light bulbs within the cooling
chamberlo turn on, even if the HEAT LOAD switch is set to OFF. With
a single bulb tumed on, the nominal heat load is currenfly applied.

. lncrease the load by setting the HEAT LOAD switch to ON (l): this will
cause the second light bulb to turn on.
 SYSTEM OVERVIEW

tr9. Wait for about 10 minutes to allow the system to stabilize.

Then, complete the remainder of the section OPERATIONAL

INFORMATION of the inspection report (except for the superheat) by
referring to the data provided by the test points in the Refrigeration
Diagram. (Keep the system running while doing this).

tr 10. Set the HEAT LOAD switch to the OFF (O) position.

Keep the system running for a while, and observe that the compressor and
condenser fan are alternately turned on and off in a cyclical way. ls this your
observation?

EYes n No

tr 11. While the compressor is running, is the condenser fan also running?

trYes tr No

tr 12. Turn off the system compressor by setting the COMPRESSOR switch to the
OFF (O) position.

Turn off the trainer by setting the POWER switch to OFF (O).

tr 13. Close the LVHVAC software.

SYSTEM OVERVIEW

IDENTIFICATION

Technician name

Date

SYSTEM INFORMATION

Description

Model number

Serial number

Refrigerant type

Metering device type

Evaporator type

Condenser type

Thermostat Setpoint

Differential

Pressure controller Cut-in pressure

Cut-out pressure

ELECTRTCAL DATA ITYPTCAL)

Compressor v (vAC)
LRA (A)

RLA (A)

Evaporator fan v (vAC)

l(A)
Condenser fan v (vAC)
t(A)
- To be completed later
 SYSTEM OVERVIEW

OPERATIONAL INFORMATION (TYPICAL}

ldle pressures and temperature Compressor pressure on LP side

(PS2)

Compressor pressure on HP side

(PS1)

Ambient temperature (T6)

Compressor running v (vAC)

with HEAT LOAD applied

t(A)

Pressures Low-pressure (PS2)

High-pressure (PS1)

Temperatures Cooling chamber (T7)

Condenser inlet (T5)

Across condenser
(r5 - 11)
Across evaporator
(lr2l - lr3l)
Superheat

OBSERVATIONS

* To be completed later

Table 1-4. lnspection report.

Name: Date:

lnstructor's approval:

REF RIG ERAT I O N TRAI N I NG S YSIEM

\
 REF RI G ERATI O N F U N D AM ENTALS

Energy

Energy is the ability to do work. Energy exists in two forms, potential and kinetic:

. Potential energy is energy a body possesses due to its position or particular

physical or chemical state.

. Kinetic energy is energy a body possesses due to its motion.

Depending on the work to be done, energy can be described as thermal.

mechanical, electrical, etc.

Energy is measured in different units, such as

. metric or S.l. units of joules (J). Since the joule is a relatively small unit, the
kilojoule (kJ) is used more often.
. imperialunits of British thermal units (Btu)in thecontextof refrigeration systems.

The relationship between the above units is as follows:

1000J=1kJ=0.949Btu

Temperature

Temperature is a measure oflhe average kinetic energy ofthe particles that make
up a body. The greater the kinetic energy of the Particles is, the higher the
temperature of the body will be.

Thermal Energy and its Transfer

Whenever two bodies of different temperatures are broughl together, the particles
of the two bodies will collide due to their random motion. The particles of the hotter
body, which have greater kinetic energy, will be slowed down by the collisions, while
the slower particles of the cooler body will get faster.

As a result ofthese collisions, thermalenergy from the hotter body will be transferred
to the cooler body. This will cause the temperature of the hotter body to decrease
and the temperature of the cooler body to increase.

This phenomena is referred to as thermal energy transfer (or heat transfer).

Thermal energy transfer, if left to itself, will continue until the particles of the two
bodies have equal amounts of thermal energy. When this condition occurs, the tvvo
bodies have equal amounls ofthermal energy. The two bodies have attained equal
temperatures and are said to be in thermal equilibrium.
REF RI G E RATI O N F U N D AM ENTA LS

There are three mechanisms by which lhermal energy transfer occurs, which are
conduction, convection, and radiation.

. Conduction: thermal energy is transferred by direct contact between the particles

ofa Single body, or between the particles of two (or more) bodies in good thermal
contact with each other.

. Convection: thermal energy is transferred between the particles of a fluid.

Convection can be natural or forced. Natural convection causes the heated fluid
to become lighter and rise up into a cooler, denser region. Forced convection is
the forced circulation of a fluid by a mechanical device such as a fan or pump.

. Radiation: thermal energy is transferred through the effects of electromagnetic

radiation. For example, the effect of radiation from lhe sun warming your face
while the surrounding air is relatively cool.

Basic Principles of Refrigeration Systems

The main function of a refrigeration system is to remove thermal energy (heat) from
a place and transfer it to another place. All refrigeration systems follow these basic
principles:

1. Thermal energy, when lost or gained by a fluid (a liquid or a gas), normally

causes the temperature of the fluid to change. The gained or lost energy that
causes a change in temperature is called sensible heat.

2. A change of state is said to occur when a fluid changes lo a gas or a liquid.

When it changes from liquid to gas, the fluid absorbs thermal energy. When it
changes from gas to liquid, the fluid loses thermal energy.

3. During a change of state, the thermal energy gained or lost by the fluid does not
cause a change in the temperature ofthe fluid. This occurs because the gained
or lost energy goes into changing only the potential energy of the fluid, not its
kinetic energy. Consequently, the gained or lost energy is called latent heat.
During a change of state, the temperature of the fluid is proportional to the
saturation pressure of the fluid.

4. Metallic parts used in a refrigeration system are selected as a function of their

thermal conductivity.

As figure 2-1 shows, a refrigeration system contains four basic devices:

- a compressor;
- a condenser;
- an expansion (metering) device:
- an evaporator.
 REF RIG ERATI O N F U N DAM ENTALS

7
I
I
REFRIGERANT FLOW
<:- LlaUlD LINE
/
H(mNStOl{ (mETER|NG)
DEVICE
4, THERMAL
ENERGY

EVAPORATOR CONDENSER
&I
SUCTION LINE

SUPERHEATED VAPOR
REFRIGERATED SMCE

I
COMPRESSOR

LOW+RESSURE HIGH.PRESSURE
(cooLING) SIDE (GoNDENSTNG) SIDE

DARK LIGHT DARK LIGHT

I I
RED RED BLUE BLUE

COLOR
tt
KEY ll L__l
HIGH. HIGH. LOW- LOW-
PRESSURE PRESSURE PRESSURE PRESSURE
GAS LIOUID LIQUID GAS

Figure 2-1. The four basic components of a refrigeration system'

The Refrigeration Cycle

ln Figure 2-1, the compressor is the heart of the refrigeration system: it makes the
refriglrant flow through the system. To do so, it creates, along with the expansion
device, a difference in pressure between the low-pressure (cooling) and high-
pressure (condensing) sides of the system'

As the refrigerant flows through the system, it gives up or absorbs thermal energy
by changing from gas to liquid, and then returning from liquid to gas'

- The compressor produces a hightemperature, high-pressure superheated

vapor(') at its HP (discharge) side.

(1)Avaporissaidtobesuperheatedwhenitstemperatureishigherthanthalnormallycorrespondingtoitscurrentpressure. lnthiscondition,
the vapor is fully saturated.

REFRI G ERATI O N TRAI N I NG SYSTEM

 REF RIGERATION F U N DAM ENTALS

- This vapor enters the condenser and, as it flows through the tubing coils, gives
up thermal energy until it turns into a high-pressure saturated liquid. Once it has
lost all its latent heat(2), the liquid is said to be subcooled(3).

- The subcooled liquid from the condenser then flows through the expansion
device, where it is forced through a restriction or a small orifice. Due to its high
resislance, the expansion device regulates the flow of refrigerant and causes a
drop in the pressure of the refrigerant, thereby decreasing its boiling point
accordingly. ThiS causes part ofthe liquid to turn into vapor, and the temperature
of the remaining liquid to decrease.

- The mixture of liquid and vapor then flows through the evaporator, where it
absorbs thermal energy until it becomes a saturated vapor. This absorption of
thermal energy causes the temperature in the refrigerated space to decrease.

The saturated vapor further absorbs thermal energy before it leaves the
evaporator, turning into a surperheated vapor. This prevents liquid refrigerant
from entering the compressor.

- This low-temperature, low-pressure superheated vapor then goes to the

LP (suction) side of the compressor, where it is compressed and turned into a
high{emperature, high-pressure superheated vapor, to start a new refrigeration
cycle.

Note: Superheat does not necessaily mean that the refrigerant is hot. ln fact,
superheated vapor can bequitecold. Similarly, subcooted does not necessarily
mean that the refigerant is cold, as it can be quite warm.

Pressure Measurements

Pressure can be measured in different units. such as

. metric units of bars (bar);

. S.l. units of kilopascats (kPa):
. imperial units of pounds-force per square inch (psi).

The relationship between the above unils is as follows:

1 bar = 101.3 kPa = 14.7 psi

To monitor a refrigeration cycle, pressure measurements must be performed along

the system. This can be performed by using pressure gauges, which provide a direcl
visual reading of the pressure on a dial.

r2) Latent heat, es earlier menlioned, is lhe energy gained or lost during a change of slate that does not cause a change in the
lemperature
of the liquid or gas.
l:) A liquid is said to be subcooled when its temperature is lower lhan that nofinally corresponding lo ils curent pressure.
 REF RIG ERATI O N F U N D AM ENTALS

There are several types of pressure gauges, including:

- absolute pressure gauges;

- gauge pressure gauges;
- compound pressure gauges.

Ab sol ute Pressure Gauges

The air pressure in outer space is 0 bar (0 psi or 0 kPa), because there is no air
(perfect vacuum). When measured with respect to vacuum, pressure is called
absolute pressure.

Absolute pressure gauges, therefore, measure pressure with respecl to vacuum. At

atmospheric pressure, they provide a non-null reading of about 1 bar absolute.
(14.7 psia or 101.3 kPa absolute). Because of this, they are not commonly used in
refrigeration systems.

'Atmospheric pressure at sea level.

Gauge Pressure Gauges

When measured with respect to atmospheric pressure, pressure is called gauge

pressure.

Gauge pressure gauges, therefore, provide a null reading of 0 bar gauge (barg) at
atmospheric pressure (or 0 psig, 0 kPa gauge, etc., depending on how the gauge is
graduated). Thus, atmospheric pressure is not included in the gauge pressure
reading.
REFRIG ERATIO N FUN DAM ENTALS

Gauge pressure gauges are commonly used in the high-pressure section of

refrigeration systems. A gauge pressure gauge is shown in Figure 2-2.

,,V,,,*

AT OSPHERIC PRESSURE
0 barg , 0 p.lg
- I bar abs. / 14.7 psla

Figure 2-2. Gauge pressure gauge (barg/psig readings).

As a summary, Table 2-1 indicates the relationship between absolute and gauge
pressure measurements, in the metric, imperial, and S.l. systems of units.

METRIC IMPERIAL s.t.

0 barg = 0 psig = 0 kPa gauge

= 1 bar abs. = 14.7 psia = 101 .3 kPa abs.

'1 barg = 14.7 psig = 101.3 kPa gauge

Table 2-1. Relationship between gauge and absolute pressure measurements.

 REF RI G ERAN A N F U N DAM ENTALS

Compoun d Pressure Gauges

Compound pressure gauges can permit the measurement of either gauge or

absolute pressures, as Figure 2-3 shows.

- The gauge can read pressures above atmospheric pressure, in barg, psig, or
kPa gauge, depending on how it is graduated.

It can also read pressures below atmospheric pressure, in bar abs., psia,
millimeters of mercury (mmHg), or inches of water (inHrO), for example,
depending on how it is graduated.

bars or pors
/

/ io 40 so

ATUOSPHERIC PRESSURE
(0barg/0pelg) --_____-->

barabs.orpeia
\
\

Figure 2-3. Compound gauge.

Temperature Measurements

ln addition to pressure measurements, temperature measurements must be

performed to monitor a refrigeration cycle.

Temperature is measured on a temperature scale. There are fourtemperature scales

whic'h are in use today: the Celsius scale, the Kelvin scale, the Fahrenheit scale, and
the Rankine scale. Appendix C shows a comparison of the four temperature scales.

ln refrigeration systems, the Celsius (S.1. and metric unit) or Fahrenheit (imperial
unit) scales are normallY used.

. The water boiling point corresponds to 100 on the Celsius scale, or 212 on the
Fahrenheit scale.

REFRI G ERAT I O N TRAI N I NG SYS TEM

R EF RIG ERATI O N F U N DAM ENTA LS

. The ice melting point corresponds to O on the Celsius scale, or 32 on the

Fahrenheit scale.

Based on these two points, temperature measuremenls can be converted from

degrees Celsius to degrees Fahrenheit, and vice versa, as indicated inTable 2-2.

S.I. OR METRIC FACTOR IMPERIAL FACTOR S.I. OR METRIC

Degrees Celsius ('C) x '1.8 + 32 = Degrees Fahrenheit ("F) 32 x 0.55 Degrees Celsius ('C)

Table 2-2. Temperature conversion.

Refrigerants

A refrigerant is a fluid that can absorb or give up thermal energy (sensible and latent
heat). The amount of thermal energy gained or lost by a refrigerant under specific
conditions is delermined by the type of the refrigerant. A property of refrigerants is
that their boiling point at any given pressure is low, in comparison with other types
of fluids.

The refrigerant used in the Lab-Volt Refrigeration Training System is R-134a. This
chlorine-free refrigeranl was designed to replace the R-12 refrigerant. lt has no effect
on the ozone layer [Ozone Depletion Potential (OZp) = O], whiie its properties make
it suitable for a variety of air-conditioning and refrigeration applications.
 REF RI G ERATI O N F U N D AM ENTALS

Table 2-3liststhe temperature-pressure relationship forthe R-134a refrigerant under

salurated condition.

REFRIGERANT TEMPERATURE REFRIGERANT PRESSURE

-17.6"C (0"F) 0.43 barg (6.3 psig)

-14.9"C (5'F) 0.61 barg (8.8 psig)

-12.1'C (10'F) 0.80 barg (1'1.6 psig)

-6.6'C (20"F) 1 .24 barg (18.0 psig)

1.1'C (30'F) 1.77 barg (25.6 psig)

4.4"C (40'F) 2.38 barg (34.5 psig)

9.9'C (50'F) 3.10 barg (44.9 psig)

15.4'C (60'F) 3.92 barg (56.9 psig)

20.9"C (70'F) 4.88 barg (70.7 psig)

26.4'C (80'F) 5.96 barg (86.4 psig)

31.9"C (eo"F) 7.20 barg (104.2 psig)

37.4'C (100"F) 8 58 barg ('124.3 psig)

42.9"C (110'F) 10.13 barg (146.8 psig)

48.4'C (120"F) 1 '1 .86 barg (171 .9 psig)

53.9'C (130'F) 13.8 barg (13.8 psig)

59.4 "C (140"F) 15.91 barg (230.5 psig)

64.9"C (150" F) 18.24 bary (264.4 psig)

Table 2-3. R.1 34a temperature-pressure .elationship.

The figures in Table 2-3 come from the reference chart shown in Figure 2-4. This
chart, provided by the refrigerant's manufacturer, is usually provided on the form of
a practical pocket guide. lt shows the temperature-pressure relationship for different
types of refrigerants (e.g. R-22, R-123, R-134a, R-404A, etc.). As indicated on the
chart, the boiling point of the R-134a is -26.'l "C (-14.9'F) at atmospheric pressure.

Oil is used in refrigeration systems to lubricate and cool the compressor and
compressor motor. Because of this, some amount of oil is present in the circulating
refrigerant.
REF RIG ERATI O N F U N DAM ENTALS

@0D, Sur".."frigerants

R.l3ila BOILING POINT

AT AT OSPHERIC PRESSURE

:l

f1

i!

;
gl

Figure 2-4. Refrigerant manufacturer's chart.

 Job Sheet
REF RI G ERATI O N F U N DAM ENT ALS

OBJECTIVE

ln this job, you will verify the pressure-temperature relationship of the R-134a
refrigerant. You will place the system into operation and sense the temperature at
various points of the system with your hand. You will then study the refrigeration
cycle by measuring the temperatures and pressures along the system.

EQUIPMENT REQUIRED

Lab-Volt Refrigeration Training System, Model 3431

PROCEDURE

Pressure-Temperature Relationship

n 1. On the control panel of the Refrigeration Training System, make sure the
main POWER switch is set to OFF (O).

Connect the Refrigeration Training System to the computer used to run the
LVHVAC software, via a USB cable. Turn on the computer and then run the
LVHVAC software.

n 2. On the Refrigeration Training System, make the following settings:

Note: Do not turn on the Refigeration Training Sysfem for now.

COMPRESSORswitch ..... OFF(O)

(see Nore)
EVAPORATOR-FAN SPEED control knob . . 1-1;61
CONDENSER-FAN SPEEDcontrol knob . . .... 3O'CLOCK
switch
HEAT LOAD . . OFF (O)
Thermostatsetpoint .....5'C(41'F)
Manually-operated valves
Vl . . . Closed (handle turned fully clockwise)
V2 . . . Closed (handle turned fully clockwise)
V3 . . . . . . . . Open (handleturned fullycounterclockwise)

Note: Iake care not to turn this knob fully counterclockwise,

which would close the knob switch and cause the fan to stay
turned off.

'*f

REF RI G ERATIO N TRAI N I NG S YSIEM

REF RI G E RAT I O N F U N DAM ENTALS

! 3. On the front panel of the trainer, locate the low-pressure (LP) and high-
pressure (HP) gauges. On each gauge, observe that there is a pressure
scale, in psig, and several temperature scales based on the lype of
refrigerant used: R-134a, R-507, and R404a.

The LP pressure gauge is of the (gauge/compound) type.

The HP pressure gauge is ofthe _ (gauge/compound) type.

tr 4. Read the pressures indicated by the gauges and record them in the
column "GAUGE PRESSURE" of Table 24.
Nolei The LP and HP pressure gauges are graduated in psig. lf
you are using the metic system of units, nultiply psig by 0.068 to
obtain barg.

GAUGE PRESSURE THEORETICAL TEMPERATURE

(barg/psig) ("c/'F)
LOW-PRESSURE
(LP) GAUGE

HIGH.PRESSURE
(HP) GAUGE

Table 2-{. Pressures and temperatures on the LP and llP sides of the system.

tr 5. ln Table 2-3 of the INFORMATION sheet, find the temperatures that

conespond to the LP and HP pressures recorded in Table 24, and record
them in the column "THEORETICAL TEMPERATURE" of Table 2-4.

Now, read the temperatures indicated on the R-134a scale ofthe LP and HP
pressure gauges of the trainer. Do these temperatures approximately
correspond to the theoretical values recorded in Table 2-4?

Notei The LP and HP pressure gauges are graduated in degrees

Fahrenheit ('F). lf you are using the metric systern of unlts,
subtract 32 from your reading and multiply the result by 0.55 to
obtain degrees Celsius ( "C).

!Yes nNo

! 6. Assume that the Refrige€tion Training System has not been run recently,
and is in a state of equilibrium. ln this condition, which of the following is
true:

a. The pressure differential across the LP and HP pressure sides of the

system is null.
The temperatures read on the R-134a scale ofthe LP and HP pressure
gauges are equal and conespond lo the room temperature.
 REF RI G ERAT I O N F U N D AMENTATS

c. lf the R-507 refrigerant were used instead of the R-134a, the

temperatures read on the R-507 scale of the LP and HP pressure
gauges would correspond to the room temperature.
d. All of the above.

Manually Sensing Temperature Along the Refrigeration System

tr 7. Set the trainer POWER switch to ON (l). Then, set the COMPRESSOR and
HEAT LOAD switches to ON (l). Let the system run for about 2 minutes.

tr B. Complete Table 2-5 by sensing the temperature at the five points indicated
in Figures 2-5 and 2-6. (ln Figure 2-5, the protecting plate along the
mounting base of the compressor/condenser assembly is not shown):

a. For point 0 (condenser expelled air), place your hand between the
condenser fan and compressor case to determine if the expelled air is
cool, warm, or hot. Record your observation in Table 2-5, next to
''CONDENSER EXPELLED AIR".

WARNING!

Be careful not to touch the compressor case, which could

become quite hot.

b. For points A, @, @, and 6, touch the refrigerant tubing at the indicated

locations.

REF R' G ERAT I O N TRAI N I NG S YSTEM

REFRIGERATION FUN DAMENTALS

SENSING POINT COOL/WARM/HOT

Condenser expelled air (point O in Figure 2-5)

Suction line (point @ in Figure 2-5)

Liquid refrigerant line (point O in Figure 2-5)

CAPILLARY 2 inlet (point O in Figure 2-6)

CAPILLARY 2 outlet (point 6 in Figure 2-6)

Table 2-5. Sensing temperature with your hand ai various points of the system.

WARI{ING I
THE CO PRESSOR CASE
AY BECO E HOT

Figure 2-5. Sensing temperature manually at points'1, 2, and 3.

 REF RIG ERATI O N F U N DAM ENTATS

*$ ?!
qo

Figure 2-6. Sensing temperature manually at points 4 and 5.

The Refrigeration Cycle

tr 9. Referring to the Refrigeration Diagram of the LVHVAC software, complete

the column 'TEMPERATURE. of Table 2-6by recording the temperatures
indicated by test points T5, T1 ,12, and T3 of the diagram.
REFRIG ERATIO N FUN DAMENTALS

TEMPERATURE THEORETICAL PRESSURE

TEST POINT
("c/'F) (barg/psi9)

Condenser inlet (T5)

Condenser outlet (T'l )

Evaporator inlet (T2)

Evaporator outlet (T3)

Table 2-6. R-134a temperaturc-pressure relationship,

n 10. ln Table 2-3 of the INFORMATION sheet, find the pressures that
correspond lo each temperature recorded in Table 2-6, and record them in
the column "THEORETICAL PRESSURE' of Tabte 2-6.

tl 11. ln Table 2-6, observe that the temperature of the refrigerant at the
condenser outlet is slightly lower than that at the condenser inlet, but that
the pressure at these two points is significanly higher than that at the
evaporator inlel.

Briefly explain what happens to the high-pressure superheated vapor from

the compressor as it flows through lhe condenser.

! 12. As the refrigerant flows through the condenser tubing coils, it loses thermal
energy by conduction through the coils, and by forced convection created
by the

tr 13. ln Table 2-6, observe that the temperature and pressure ofthe refrigerant
at the condenser outlet are significantly higher than those al the evaporator
inlet.

Briefly explain what happens to the high-pressure subcooled liquid from the
- as it flows through the expansion device CAPILLARY 2.
condenser
 REF RI G ERATI O N F U N DAMENTATS

tr 14. As the refrigerant (mixture of gas and liquid) flows through the evaporator,
thermal energy from the warmer air in the cooling chamber transfers to the
refrigerant, through the evaporator tubing by , and
through air recirculation by the created by the
evaporator fan.

tr 15. ln the column "GAUGE PRESSURE" of Table 2-7, record the pressures
currently indicated by the LP and HP gauges on the trainer front panel.

THEORETICAL ABSOLUTE
GAUGE PRESSURE PRESSURE
TEMPERATURE
(barg/psig)
("c/'F) (bar abs./psia)

LOW-PRESSURE
(LP) GAUGE

HIGH-PRESSURE
(HP) GAUGE

Iable 2-7. Pressures and temperatures on the LP and HP sides of the system'

n 16. ln Table 2-3 of the INFORMATION sheet, find the temperatures that
correspond to the LP and HP pressures recorded in Table 2-7 , and record
them in the column 'THEORETICAL TEMPERATURE" of Table2-7.

tr 17. Convert the LP and HP gauge pressures recorded in Table 2-7 inlo absolute
pressures and record your results in the column "ABSOLUTE PRESSURE"
of this table.

To do so, add the atmospheric pressure (1 bar abs., or 14.7 psia) to the
gauge pressure reading to obtain the equivalent absolute pressure.

For example:

1.2barg + 1 bar abs. = 2.2bar abs.

or
20 Psig + 14'7 PSia = 34'7 Psia

! 18. Calculate and record below the current pressure differential, AP, across the
compressor.

AP = HP gauge reading - LP gauge reading

AP= bar or _ psi

REF RIG ERATI O N T RAI N'A'G SYSTEM

REF RI G E RATI O N F U N D AM ENTA LS

! 19. Set the CONDENSER-FAN SPEED control knob to OFF (O). (This sets the
knob switch to the open condition.)

Let the system run, and observe what happens to the LP- and HP-gauge
pressure readings on the trainer front panel.

Observe that the pressure differential across the compressor becomes

increasingly higher with time, until the pressure on the Hp side reaches
about '12-barg (17s-psig), causing the high-pressure controller reset breaker
to trip (you will hear a click as the breaker trips) and the compressorto stop.
ls this your observation?

!Yes !No

Briefly explain why the pressure differential across the compressor

increased over time after the condenser fan was turned off.

a 20. Refer to Figure 2-7. Since the controller reset breaker has tripped, the
breaker blade has popped out. Wait a couple of minutes to lel the pressure
differential drop. Push in on the blade to reset the breaker, which should
cause the compressor to start running again. Turn ofl the compressor by
setting the COMPRESSOR switch to the OFF (O) position.

Note: Make sure the compressor is running and the controller

reset breaker has nottipped again when you setthe compressor
switch to O. lf the reset breaker has tripped and the compressor
is inoperative, wait unit the pressure differential has dropped
significantly, and then reset the breaker to restaft the compressor.
Then tum off the compressor while it is running.
 REF RI G ERAT I O N F U N D AMENTA tS
PUSH IN ON RESET BLADE
TO RESTART COMPRESSOR

Figure 2-7 . Gontroller reset breaker.

! 21. Set the HEAT LOAD switch to the OFF (O) position.

Then, turn off the trainer by setting the POWER switch to OFF (O).

tr 22. Close the LVHVAC software.

Name: Date:

lnstructor's approval :
;

l
)
 REFRIGERATION COMPO,MMS FART 0

!ntroduction

As mentioned earlier, a refrigeration system consists of refrigeration components,

as well as instrumentation and control components.

The basic refrigeration components are'. a compressor, a condenser, an

expansion device, and an evaporator. Additional refrigeration components are
necessary to ensure the safe and efficient operation of the system, as well as its
maintenance and troubleshooting, as Figure 3-1 shows:

- a liquid receiver;
- a filter/drier;
- a moisture/liquid indicator;
- a suction line accumulator;
- service valves.

ln this job sheet, you will study the operation of the components highlighted in
Figure 3-1 . You will study the operation of the other components in the next exercise.
 REFRTGERATTON COMPOTVEVTS (PART 0

EVAPORATOR sPAl{stoN ( ETERrl{c)

DEVICES

MANUAL
VALVES

MOISTURE /
LIOUID
INDICATOR

SUCTION
FILTER /
DRIER

<-- LIOUID
RECEIVER

CO PRESSOR
DISCHARGE

CONDENSER

Figure 3-1. Retrigeration components of the system.

Compressor

The compressor draws low-pressure superheated vapor from the cooling (Lp) side
of the system at its suction inlet. lt compresses it to a high-pressure superheated
vapor and expels it, through its discharge outlet, to the condensing (Hp) side of the
system.

Figure 3-2 shows the compressor used on the Refrigeration Training System. This
compressor is of the reciprocating type. lt is said to be hermetic because it is
totally encased in a sealed housing. The housing contains an electric motor, a crank
shaft, a single cylinder, and lhe compressor. (Note that reciprocating compressors
can have more than one cylinder).
 REFRTGERATION COMPONEMS FART t)

The rotation of the motor and crank shaft makes the cylinder piston move back
and forth (reciprocate). For every compression stroke ofthe piston, a new volume
of vapor is compressed and discharged at a high pressure.

The motor is cooled by the transfer of thermal energy from the stator to the case
(conduction), and by passing the returning vapor around the motor windings
(forced convection) before it is compressed.

A length of tubing (called process stub) connected to the case provides access
to the refrigerant inside the compressor for servicing purposes, and can be
resealed once lhe compressor is repaired. However, hermetic compressors are
often replaced instead of repaired, because lhe compressor case is welded
closed.

The compressor needs a certain amount of oil for lubrication of its moving parts.

sucnox (hrLET) UtlE

col{PRESSOR
TERIIINAL DISCHARGE (OUTLET} LINE
COVER

PROCESS
TUBE (STUB)

Figure 3.2. Reciprocating hermetic compressor of the Refrigeration Training System.

C o m p re ssor Cha racleristlcs

lmportant characteristics of a compressor are the volumetric flow rate, the

volumetric efficiency, and the compression ratio.
. The volumetric flow rate is the volume of gaseous refrigerant discharged by the
compressor per unit of time. The formula for calculating the theoretical
volumetric flow rate is as follows:

Notei r/min stands for revolutions per minute.

Metric units:

volumetric flow rate(r"r.in) = Displacement(m3/r) . 5haft speeduT,niny

REFRTGERATTON COMPONE TTS ?ART t)

lmperial units:

Volumetric flow ratelr3rmin; = Displacemen\fl3/i . speed,,rmin)

"n.L
When the compressor is of the reciprocating type, the volumetric flow rate is the
volume displaced by the cylinder(s) on each piston stroke (distance traveled from
bottom to top):

n2
v.'4 rTu L.N.n
where Vp = Volumetric flow rate [m3/min or ft3/min)]
D= Diameter of cylinder piston (m or ft)
L= Length of the piston stroke (m or ft)
N= Compressor speed (number of revolutions/min)
n= Number of cylinder(s)

. The actual volumetric flow rate of the compressor is less than the theoretical
volumetric flow rate because of internal pressure losses across the cylinder
valves. The ratio of actual volumetric flow rate to theoretical volumetric flow rate
is called the volumetric efficiency. lt is expressed as:

Actual volumetric flow rate . 100

Volumetric efficiency(%)
Theor. volumetric llow rate

Small compressors used in domestic refrigeration syslems have volumetric

efficiencies between 40 and 75o/o, with 50% being an average value. Larger
commercial compressors have volumetric efficiencies between 50 and 80%, with
70% being an average value.

The compression ratio (a pure number) indicates the efficiency of the

compressor when using a particular refrigerant. lt is expressed as:

Absolute pressure on suction side

Compression ratio =
Absolute pressure on discharge side

For a single stage reciprocating compressor, the maximum allowable

compressor ratio should be below 10. Table 3-1 lists typical compression
ratios for different refrigerants under normal conditions of 30"C (86"F)
condensing temperature and -15'C (5'F) evaporating lemperature. A value
of 4.7 for refrigerant R-134a means that the absolute discharge pressure
should be less than 4.7 times that of the absolute suction pressure. A higher
ratio can result in a loss of efficiency and in possible damage to the
compressor.

"The compression rulio oI 4.7 for the R-134a refrigerant is for a condensing
temperature of 54.4"C (130'F) and an evaporating temperature of 1.7'C
(35"F).
 REFRTGERATTON COMPONENTS qART t)

REFRIGERANT COMPRESSION RATIO

R-22 4.16

R-134a* 4.70

R-717 4.94

R-718 6.95

R-744 3.10

R-764 5.61

Table 3-1. Maximum typical compression ratios for different refrigerants'

Liquid Receiver

The liquid receiver is normally placed downstream of the condenser. lt stores liquid
refrigerant in excess and ensures a constant supply of liquid to the expansion device.
The liquid receiver is used in refrigeration systems that use an expansion valve as
the expansion (metering) device. The liquid receiver is unnecessary when the
metering device is a capillary tube, because in that case, all the liquid refrigerant
remains stored in the evaporator.

Typically, the liquid receiver should be large enough to hold all the refrigerant in the
system, because it will have to store all the refrigerant when the system is shut down
for repair or servicing.

Figure 3-3 shows a liquid receiver of the same type as the one installed on the
Refrigeration Training System. The receiver is designed for vertical mounting. The
receiver outlet is equipped with a Rotalock@valve used for initial refrigerant filling.

ROTALOCK
VALVE

INLET
(FROM CONDEI{SER OUTLET)

OUTLET
GO FTLTER DR|ER)
'

Figure 3-3. Liquid receiver of the Refrigeration System.

REFRTGERATTON COMPOTVEVTS PART t)

FiltedDrier

The filter/drier is normally installed downstream of the liquid receiver. The filter
removes contaminanls such as dust, dirt, metal fillings, rust, from the flowing
refrigerant to prevent clogging of the small restriction of the expansion device and
damage to the compressor. The drier collects and holds moisture from the
refrigerant. The arrow points in the direction of refrigerant flow (from inlet to ouflet).

DIRECTION OF OUTLET
REFRIGERANT FLOW

Figure 3.4. Fitter/drier.

Moisture/Liquid lndicator

The moisture/liquid indicator is normally installed just upstream of the expansion

(metering) device. lt consists of a sight glass and a sensing element that are used
to check the charge and condition of the flowing liquid refrigerant, as Figure 3-5
shows.

. Bubbles seen through the sight glass can indicate a lack of refrigerant, a low
discharge pressure, or some form of restriction in the liquid line.

. The color of the sensing element changes as the amount of moisture in the
refrigerant changes. By matching the color of the element with the colors on the
surrounding scale, the moisture content can be determined. With refrigerant
R-134a, for example, dark blue is often used to indicate a dry system and a
salmon color indicates a wet system. (However, the color selection is arbitrary
and varies by manufacturer).
 REFRTGERATTON COMPONENTS qART t)

COLOR
SCALE

SENSING
ELEMENT

Figure 3-5. Moisture/liquid indicator.

Suction Line Accumulator

The suction line accumulator is placed just upstream of the compressor. lt is used
to prevent sudden surges of liquid refrigerant and oil from reaching the compressor.
Refrigerant flood back to the compressor is a frequent cause of broken compressor
valves, blown gaskets, and bent connecting rods.

OUTLET INLET
FO COMPRESSOR) (FROI EVAPORATOR)

LEAK+ROOF
FUSIBLE PLUG

METERING HOLE

Figure 3-6. Suction line accumulator.

REFRTGERATTON COMPOTVEVTS PART 0

Accumulators are either vertical or horizontal. Figure 3-6 shows a vertical

accumulator. lt consists of a U-shaped tube with a small metering hole at the bottom,
where small amounts of liquid refrigerant and oil are temporarily collected. The
metering hole sends this mixture with the gaseous refrigerant, at a controlled rate,
to the compressor. Since the liquid boils as it flows through the suction line, only the
oil and refrigerant go to the compressor.

It is very important that the inlet and outletofthe accumulator be correcfly connected
to prevent refrigerant and oil from becoming trapped. The selection of an
accumulator is based on the following factors:

. the pressure drop created by the accumulator, which must not be too high;

. the ability of the accumulalor lo return refrigerant at an adequate rate;

. the refrigerant holding capacity ofthe accumulator, which should not be less than
50% of the total system refrigerant capacity;

. the diameter, length, and orientation of the accumulator, which must suit your
application.
 REFRTGERATTON COMPONEVTS (PART 0

OBJECTIVE

ln this job, you will study the operation and characteristics of the following
refrigeration iomponents: cLmpressor, liquid receiver, filter/drier, liquid indicator, and
suction line accumulator.

EQUIPMENT REQUIRED

Lab-Volt Refrigeration Training System, Model 3431

PROCEDURE

Compressor

tr 1. Examine lhe compressor at the rear bottom of the Refrigeration Training

system. Record below the name of each compressor component' as
identified by the circled letters in Figure 3-7

a. d.

b. e.

C.

Figure 3-7. ldentifying the comPressor components

REFRTGERATTON COMPOTVEVTS (PART D

E 2. Examine the suction and discharge refrigerant lines of the compressor.

The tubing that goes to the suction inlet ofthe compressor comes from the
ouflet of the

The tubing going out of the discharge ouflet of the compressor, which ts
bent into several loops, is connected to the inlet of the

tr3. Locate the manufacturer's label affixed on the mounting base of the
compressor/condenser aSSembly. Obtain and record the following
compressor information:

Manufacturer's name:

Serial number:

Model number:

Refrigerant:

Voltages
50 Hz:
60 Hz:

Nominal pressures
High side:
Low side:

Locked-rotor current (LRA):

Prolection:

Additional informalion: (For example, the volumetric displacement of the

compressor, to be found in the manufacturer's documenlation or on the
manufacturer's Web site).

Measuring the Compression Ratio

tr 4. On the control panel of the Refrigeration Training System, make sure the
main POWER swilch is set to OFF (O).

Connect the Refngeration Training System to the computer used to run the
LVHVAC software, via a USB cable. Turn on the computer and then run the
LVHVAC software.
 REFRIGERATTON COMPOTVENTS PART D

tr5. On the Refrigeration Training System, make the following settings:

Do not turn on the Refrigeration Training System for now.

COMPRESSORswitch ..... OFF(O)

EVAPORATOR-FANSPEEDcontrolknob. .'. HIGH
CONDENSER-FAN SPEED control knob . Half of HIGH
HEATLOADswitch . '.. ON(l)
Thermostatsetpoint .....5'C(4'1'F)
Manually-operated valves
Vl . . . . . . . . Open (handleturnedfullycounterclockwise)
V2 . . . Closed (handle turned fully clockwise)
V3 ... ... Closed(handleturnedfullyclockwise)

tr6. Turn on the Refrigeration Training System, then turn on the compressor.

ln the LVHVAC software, locate the section system Performance of the

Refrigeration Training System panel, to the right of the Refrigeration
Diagram.

The section Sysfem Pefformance displays the values of the parameters

used to assess the performance of system:the Superheat, the Compression
Ratio, the Net Refrigeration Effect, etc. The display of these values is
continuously refreshed as the refrigeration cycle progresses.

! to let the system stabilize. Meanwhile, record

7. Wait for about 10 minutes
below the maximum compression ratio recommended for the refrigerant
used (R-134a), as indicated in Table 3-1 .

Typical compression ratio:

tr 8. After about '10 minutes, the system should be in equilibrium, as indicated by

a constant pressure differential across the compressor LP- and LP-pressure
sides.

Record below the compressor suction and discharge pressures, based on

the readings of the LP- and HP-pressure gauges of the trainer'

Suction (LP) pressure:

Discharge (HP) pressure:

REFRIG ERATI O N T RAI N I NG SYS TEM

REFRTGERATTON COMPONEVTS (qART t)

! 9. Convert the gauge pressures recorded in the previous steps into absolute
pressures, and then calculate the compression ratio:

Compression ratio _ Absolute pressure on suction side

Absolule pressure on discharge side

ls the experimental resultforthe compression ratio lowerthan the maximum

allowable ratio of 10 (fora single-stage reciprocating compressor), indicating
efficient operation of the system? Explain.

ls the experimental result for the compression ratio approximalely the same
as the value displayed in the section System peiormance of the
Refrigeration Training System panel of the LVHVAC software? Explain.

n 10. Let the system run for the remainder of this job sheet.

Note: l,yhen the system is allowed to run for a ceiain time,

condensation may form on the thermostatic expansion valve
(which is nomal), causing drops of water to fallinto the collecting
tray just below the capillaies.

Liquid Receiver

n 11 . Examine the liquid receiver at the rear bottom of the Refrigeration Training
System. This device ls used to store from the
condenser.

n 12. Record below the name of each part of the liquid receiver, as identified by
the circled lefters in Figure 3-8.

a.

b.
 REFRTGERATTON COMPONEMS PART t)

Figure 3-8. ldentifying the receiver parts.

! 13. The tubing that goes to the inlet of the liquid receiver comes from the outlet
of the

The tubing that goes out of the liquid receiver is equipped with a
for initial filling purposes, and it is connected to the
on the trainer front panel.

tr 14. On the liquid receiver, find and record the following manufacturer's
information:

Modelnumber:

Refrigerant compatibility:

ls the liquid receiver compatible with the refrigerant R-134a used in the
Training System?

EYes trNo

tr 15. Table3-2showsthemanufacturer'sspecificationsforvariousmodelsofthe
liquid receiver used on the Training System.

ls the receiver model used on the Training System large enough to hold all
'1.1 kg
the refrigerant in the system, given a nominal system charge of
(2.41b)? ExPlain.
REFRTGERATTON COMPOTVENTS eARr D

PUMP DOWN CAPACITY

MODEL NUMBER
R-134a R-22 R-404a/R-507

1920 o.el ks (2.0|b) 0.el ks (2.0|b) 0.82 ks (1.8 lb)

s-8060 1.1 kg (2.a lb) 1.1 ks (2.4|b) 0.9 kg (2.0 lb)

s-8061 1.1 kg (2.a lb) 1.1 kg (2.a lb) 1.0 ks (2.1 lb)

s-8062 1.5 ks (3.3 lb) 1.5 ks (3.3 lb) 1.3 ks (2.8 lb)

s-8063 2.0 ks (4.31b) 1.9 ks (4.2 lb) 1.7 kg (3.7 lb)

Table 3.2. Liquid-receiver man ufacturer,s chart.

Filter/Drier and Moisture/Liquid lndicator

tr 16. Examinethefilter/drier,locatedjustdownstreamofthesolenoidvalveonthe
trainer front panel. This device removes from the
flowing refrigerant to prevent clogging of the and
damage to the compressor. The drier collects and holds
from the refrigerant.

n 17. According to the manufacturer's information found on the filter/drier, is this

device compatible with the refrigerant R-134a?

E Yes fl No

on the filter/drier, observe that there is an arrow. what does this arrow
indicate?

n 18. Locate the moisture/liquid indicator just downstream of the filter/drier.

observe that liquid refrigerant can be seen flowing through the sight glass.
Too much bubbles or foaming seen through this glass cin indicate
a. a lack of refrigerant.
b. a low discharge pressure.
c. some form of restriction in the liquid line.
d. All of the above.
 REFRTGERATTON COMPONENTS eARr 0

tr '19. By matching the color of the sensing element of the moisture/liquid indicator
to one of the colors on the surrounding scale, determine the moisture
content of the refrigerant. ls the system dry, wet, or within the caution area?

Suction Line Accumulator

tr 20. ExaminethesuctionlineaccumulatorattherearbottomoftheRefrigeration
Training System. This device is used to prevent sudden surges of
and from reaching the
compressor.

n 21 . Record below the name of each part of the accumulator, as identified by the
circled letters in Figure 3-9.

a.

b.

c.

Figure 3-9. ldentifying the accumulator parts.

tr 22. The tubing that goes to the inlet of the accumulator comes from the outlet
of the

The tubing that goes out of the accumulator is connected to the

REFRTGERATTON COMPOTVENTS PART t)

! 23. According to the manufacturer's information found on the accumulator case,

is the accumulator compatible with the refrigerant R-134a used in the
Training System?

trYes nNo

! 24. Table 3-3 shows the manufacture/s specifications for various models of the
accumulalor used on the Training System.

Find the model number of lhe accumulator used on the Training System (as
indicated on the accumulator casing). According to Table 3-3, is this
accumulator large enough to hold at least 50% of the refrigerant in the
system, given a nominal system charge of 1.1 kg (2.4 lbl?

MOUNTING (VERTICAL MAXIMUM REFRIGERANT HOLDING CAPACITY

PART NUMBER
oR HORTZONTAL)
R-12 R-134a R-22 R-404a

3680 Vertical 0.8 kg 0.7 kg 0.7 kg 0.6 kg

(1.7 rb) (1.5 rb) (1.5 rb) (1.3 rb)

3816 Vertical 't .1 kg 1.0 kg 0.95 kg 0.9 kg

(2.4lb) 12.2 tb) (2.1 tb) (1.9 rb)

3817 Vertical 2.1 kg 1.9 kg 1.9 k9 0.9 kg

(4.6 rb) (4.2 tb) (4.2 tbl (1.9 rb)

3815 Horizontal 0.8 kg 0.7 kg 0.7 kg 0.6 kg

(1.7 rb) (1.5 rb) (1.5 rb) (1.4 rb)

3673 Horizontal 1.1 kg 1.0 kg 1.0 kg 0.9 kg

(2.4 tb) (2.2 tb) (2.2 tb) (1.9 rb)

Table 3-3. Suction accumulalor manufacturer's chart.

 \,
REFRIGERATION COMPONE VTS eARr 0

tr 25. On the trainer front panel, set the COMPRESSOR switch and HEAT LOAD
switch to the OFF (O) position.

Turn off the trainer by setting the POWER switch to OFF (O).

26. Close the LVHVAC software.

Date:

I nstructor's approval :
 REFRIGERATION COMPOTVEMS qART tt)
AND ENTHALPY DIAGRAM

lntroduction

ln the previous job sheet, you familiarized yourself with part of the refrigeration
components that make up a basic refrigeration system. ln this job sheet, you will
study the remainder of these components: the condenser, the expansion
(metering) device, and the evaporator, as Figure 4-1 shows.

EVAPORATOR EXPANSION (METERING)

L.- AIUAL
VALVES

OISTURE
LIOUID '
INDICATOR

FILTER /
DRIER
^stsilil.?sFJ

fi_ LIQUID
RECEIVER

COMPRESSOR

Figure 4-1. Refrigeration components of the system.

R E F R I G ER AT I O N IRA'IV"VG SYSIEM
 REFRTGERATTON COMPOTVENTS ?ART t0
AND ENTHALPY DIAGRAM

You willthen familiarize yourself with the pressure/enthalpy diagram of a refrigerant.

You will learn how this diagram can be used to graphically represent the refrigeration
cycle of a system.

Condenser

The condenser removes thermal energy from the superheated vapor discharged
by the compressor, turning it into a saturated liquid. At the outlet of the condenser,
this liquid, because it has lost all its latent energy, is said to be subcooted.

The thermal energy removed by the condenser is transferred to the surrounding air,
as long as the temperature of the air stays lower than the condensing temperature
of the refrigerant.

- As Figure 4-2 shows, a condenser consists of copper or aluminum tubing bent in

a serpentine shape through which the refrigerant is conducted.

- As the refrigerant flows through the tubing, thermal energy from the refrigerant
transfers to the coils by forced convection and by conduction.

THERMAL
ENERGY
REJECTED
\lt
-*
\t/
FROtf, COMPRESSOR
HIGH+RESSURE SUPERHEATED VAPOR

&I**
HIGH+RESSURE LIQUIO REFRIGERANT

METER|NG DEvlcE / t\
+\
THERMAL
ENERGY
REJECTED

Figure 4-2. Removal of thermal energy through the condenser tubing.

Thermal energy from the tubing then transfers to the air flowing across the coils
by convection, causing the temperature of the refrigerant to decrease. The
convection is forced by a fan. The higher the rotation speed of the fan is, the
faster the circulation of fresh air across the tubing and, therefore, the higher the
rate of thermal energy transfer between the tubing and the air.

Attached to the tubing is a web of thin metallic fins that increase the surface of
thermal energy transfer between the tubing and the surrounding air, which further
increases the rate of thermal energy transfer by forced convection.
 REFRIGERATTON COMPOTVEMS (PART tt)
AND ENTHALPY DIAGRAM

Figure 4-3 shows the condenser used on the Refrigeration Training System.

(A) REARVTEW (b) FRONTVTEW

Figure 4-3. Condenser used on the Refrigeration Training System.

Expansion (Metering) Device

The expansion device is connected between the condenser and the evaporator. lt
makes the breakpoint between the high- and low-pressure sides of the system.

The expansion device consists of a restriction or small orifice, through which the
liquid refrigerant from the condenser is forced to flow. This creates a drop in the
pressure of the refrigerant, thereby decreasing its boiling point accordingly. This
in turn causes part of the liquid to turn into vapor, and the temperature of the
remaining liquid to decrease.

Due to its high resistance to the flow of refrigerant, the expansion device regulates
(meters)this flow to the evaporator.

The Refrigeration Training System has two types of expansion (metering) devices:

. capillary tubes, which have a fixed restriction (orifice size); and

. a thermostatic expansion valve, whose restriction can be adjusted.

Capillary Tube

A capillary tube is a simple length of tube having an inside diameter smaller than
that of the main refrigerant line, as Figure 4-4 shows. Because of this, the capillary
tube restricts and meters the liquid refrigerant.

R EF RI G E RAT I O N TRAI N I NG S YSTEM

REFRTGERATTON COMPOTVEVTS qART tD
AND ENTHALPY DIAGRAM
The friction and evaporation of the refrigerant that takes place within the tube are
responsible for the pressure drop created across the capillary tube. The longer the
capillary tube, the greater the created pressure drop, for any given diameter of the
tube.

The Refrigeration Training System comes with two capillary tubes, mounted on the
front panel, just ahead ofthe evaporator. They both have the same inner diameter,
but they are of differing lengths, allowing you to test the effect that this difference
makes on the operation of the system. Since capillary tubes offer a flxed restriction
to refrigerant flow, they do not have the ability of thermostatic expansion valves
(TEV'S) to adapt to significant changes in the heat load.

REFRIGERAI{T FLOW
SiIALL.DIA*IETER
CaPTLLARY IUBTNG
J--l

HIGH+RESSURE
LOW+RESSURE SUBCOOLED LIQUIO
IXTURE FRO COT{DENSER
TO EVAPORATOR

LARGEROIATETER
REFRIGERA T TUBIiIG

Figure 4-4. capillary tube op€ration.

Thermostatic Expansion Valve (TEV)

A thermostatic expansion valve (TEV) is a device that meters the flow rate of
refrigerant to the evaporator by adapting it to any changes in the heat load. lt allows
more refrigerant to flow when the evaporalor warms up and, conversely, it allows
less refrigerant to flow when lhe evaporator cools down.

A TEV consists of a diaphragm wlth a valve and seat, and a spring that is adjusted
to obtain the desired level of superheat. As Figure 4-5 (a) shows, an external
thermal bulb, partly filled with liquid refrigerant, senses the temperature of the
refrigerant at the outlet of the evaporator.

. The difference between the temperature sensed by the bulb and that of the
refrigerant in the evaporator results in a pressure difference that acts on the
spring of the TEV to modify the TEV opening accordingly.

. Thus, when the sensed temperature becomes lower than the TEv-superheat
setting, the TEV opening is decreased to reduce the flow of refrigerant entering
the evaporator. Conversely, when the sensed temperature becomes higher than
the TEV-superheat setting, the TEV opening is increased to increase the flow of
refrigerant entering the evaporator.
 REFRTGERATTON COMPONEVTS (PART lt)
AND ENTHALPY DIAGRAM
. When the compressor is stopped, the valve is automatically closed to stop the
flow of refrigerant to the evaporator.

On the Refrigeration Training System, the TEV is mounted on the front panel of the
trainer, just ahead of the cooling chamber. As Figure 4-5 (b)shows, the thermal bulb
of the TEV is attached to the suction line of the system.
REFRTGERATTON COMPONE TTS qART t0
AND ENTHALPY DIAGRAM

THERMAL
BULB

LIOUID
LINE
(a) Thermostatic expansion valve construction

_ EVAPORATOR

TO SUCTION
- LINE

(b) Thermal bulb and capillary tube connected

to evaporator inlet (trainer interval view)

Figure 4-5. Thermostatic expansion valve.

Evaporator

The evaporator, located within the cooling chamber, turns the mixture of liquid and
gas refrigerant coming out of the expansion device into a Iow-pressure
superheated vapor. ln the process, the evaporator removes thermal energy from
the cooling chamber.
 REFRTGERATTON COMPONETVTS PART il)
AND ENTHALPY DIAGRAM
An evaporator is basically
'Figure
constructed the same as a condenser. As
4-6 shows, the evaporator consists of copper or aluminum tubing bent in a
serpentine shape through which the refrigerant is conducted.

COOLING CHAilIBER

THERTIAL
LOW+RESSURE
ENERGY
SUPERHEATED VAPOR
ABSORBED

\l /
tl
""rt'rI * COMPRESSOR SUCTION

/l\
/l\ EXPANSION DEVICE

THERMAL
ENERGY
LOW+RESSURE TTIXTURE OF
LIQUIDAND GAS
ABSORBED

Figure 4-6. Absorption of thermal energy through the evaporator tubing.

As the refrigerant (mixture of gas and liquid) flows through the evaporator,
thermal energy from the warmer air in the cooling chamber transfers to the
refrigerant, through the evaporator tubing, by conduction, and through air
recirculation by the forced convection created by the evaporator fan.

The higher the rotation speed of the fan is, the faster the recirculation created by
the fan and, therefore, the higher the rate of thermal energy transfer between the
surrounding air and the refrigerant.

Attached to the tubing is a web of thin metallic fins that increase the surface of
thermal energy transfer between the tubing and the surrounding air, which further
increases the rate of thermal energy transfer by forced convection.

As it flows through the tubing of the evaporator, the refrigerant absorbs thermal
energy (sensible heat). This increases its temperature to the boiling point. As it
further absorbs thermal energy (latent heat), the refrigerant turns into dry vapor.
The vapor then flows from the evaporator outlet to the suction side of the
compressor.
REF RtG ERATT O N CO M pOrVErVrS (p ART I 0
AND ENTHALPY DIAGRAM
Figure 4-7 shows the evaporator of the Refrigeration Training System. This
evaporator is of the forced-circulation type, and is enclosed, along with an electric
fan, in a compact metal housing.

AIR FLOW OUT

ELECTRICAL
wlRII{G TO
HEAT LOAD
(LIGHT BULBS)

FRO EXPANSPN DEvlcE

t-.-
sucnoN Lll{E AccuItluLrAToR
o fl,.....*ro

AIR FLOW II{

ff DRAII{

Figure 4-7. Evaporator used on the Refrigeration Training System.

Enthalpy Table

The amount ofthermalenergy per unit ofmass ofa refrigerant is called enthalpy (or
heat content).

Enthalpy can be measured in different units, such as

. metric or S.l. units of kilojoules per kilogram (kJ/kg);

. imperial units of British thermal units per pound-mass (Btu/lbm).

As it flows through the evaporator to refrigerate the space, the refrigerant absorbs
lhermal energy. Consequently, the enthalpy of the vapor at the ouflet of the
evaporator is greater than that of the liquid al the inlet of the expansion device. The
thermal energy absorbed per unit of mass of the refrigerant is called the
refrigeration effect.

Refrigerant manufacturers normally provide tables indicating the enthalpy of their

refrigerants at various temperatures. Appendix D, for example, is a table indicating
the enthalpy of saturated liquid and vapor for the R-134a refrigerant, at different
temperalures. Take a look at this table.
 REFRIGERATION COMPOTVE TTS PART t0
AND ENTHALPY DIAGRAM
Pressure-Enthal py Diagrams

ln addition to tables, refrigerant manufacturers provide diagrams that show the

enthalpy of their refrigerant as a function of absolute pressure. The
pressure/enthalpy diagram of the R-134a, for example, is shown in
Figures 4-8 (S.1. units) and 4-9 (imperial units).

. The horizontal axis of the diagram is graduated in enthalpy units, while the
vertical axis is graduated in absolute pressure units.

. Two curves on the diagram indicate the changes in state between saturated
vapor (right-hand curve)and saturated liquid (left-hand curve).

. Between these two curves are horizontal lines of constant temperature.

. A point representing the current refrigerant properties (pressure, enthalpy, and

temperature) that is located on a horizontal line indicates that the refrigerant is a
mixture of tiquid and vapor. lf this point is located on or to the right of the
saturated vapor curve, the refrigerant is superheated. lf this point is located on
or to the left of the saturated liquid curve, the refrigerant is subcooled.
 REFRIGERATTON COMPOTVEVTS ?ART t0
AND ENTHALPY DIAGRAM
ABSOLUTE ABSOLUTE
PRESSURE PRESSURE
(liP., abe.) (b.r, ab..)

4n

I )ul'rrnt l l uolochcnr ie.rls

10 100
HFC-134a
I Pressure Enthalpy Diagram 80 CRINCAL
PRESSURE
6 {SlUnits)
60 AREA

4 40

20

SATUMTED
1 LIQUID
LINE
0.8 8
0.6 6

0.4 4

o.2 2

0.1
SATURATED
0.08 VAPOR
0.06 uitE

0.04

0.02

0.01 ET{THALPY
(kJ /ks)
100 250 I 300

=2l0kJ/kg =270kJrkg

Figure 4-8. Pressure/enthalpy diagram for the R-134a (S.1. units).

 REFRIGERATTON COMPOTVEVTS (PART tt)
AND ENTHALPY DIAGRAM

ABSOLUTE
PRESSURE

,,1
i l^<
la' CRMCAL
I)trl)rutl l lrrotircltcttt icals sl t9 I PRESSURE
1000
HFC-134a ,o lt
o
V, AREA
800 Pressure-Enthalpy Draqram @ z
tcr
600 (ErElish Units)
i ,\
400

ili li5l I
li

is.f'o,K
El lr;l o
@
ti

SATURATED
100 LIOUID
LIE
80
60

40 SATURATED
VAPOR
LII{E

10
I
6
t !'i
4 I
q Qqea o ooo
o o 99oo o cioo
I I
7P!
:ss
c5oci
ra,

c,
(o .DO,
o o oo oo ddc'o
ESdee W
't I lUlll;
o' o oro'
tttlti.t;
I ;-8ot 1,4 ):-tt

'll,'t ENTHALPY
(Btu / lbm)

=25Bh!rlbm =53Btu/lbm

Figure 4-9. Pressure/enthalpy diagram for the R-134a (imperial units).

R EF RIG E RATI O N IRA'^"/VG SYSIE'}'

REFRTGERATTON COMPONEVTS FART il)
AND ENTHALPY DIAGRAM
The pressure/enthalpy diagram ofa refrigerant can be used to determine the amount
of thermal energy absorbed or removed by the refrigerant between two points.

ln Figure 4-8, for example,

a point indicates that at 50"C, saturated liquid refrigerant contains around

270 kJlkg of enthalpy, while another point indicates that at 7"C, saturated liquid
refrigerant contains 210 kJ/kg of enthalpy;

consequently, if a decrease in liquid temperature from 50"C to 7'C occurs

through an evaporator, each kilogram of liquid entering the evaporator
theoretically loses 60 kJ of thermal energy. However, the actual decrease in
temperature produced under these conditions will be lower, due to the fact that
latent thermal energy (latent heat of vaporization) is absorbed by the liquid
changing to vapor in the evaporator.

Graphical Representation of the Refrigeration Cycle

The refrigeration cycle of a syslem can be represented by a simplification of the

pressure-enthalpy diagram of the refrigerant it uses. The refrigerant cycle is a
quadrilateral representing the refrigerant properties (pressure, temperature,
enthalpy) at any point of the cycle.

Figure 4-10, for example, shows a refrigeration cycle ofthe Lab-Volt Refrigeration
Training System, displayed in the LVHVAC software. lcons indicate the typical
equipment associated with each phase of the refrigeration cycle.

. The horizontalline O ts O corresponds to a change ofstate from vapor to liquid,

as the refrigerant flows through the condenser. The temperature and absolute
pressure of the refrigerant stay constant, but the enthalpy decreases from right
to left. The pressure is at lhe compressor discharge (HP) level.

. At point O, high-pressure subcooled liquid reaches the inlet of the expansion

device.

. Between points O and g, the refrigerant flows through the expansion device: its
absolute pressure drops, while its enthalpy stays conStant. Part ofthe liquid tums
into vapor.

. The horizontalline g { O corresponds lo a change of state from liquid to vapor,

as the refrigerant flows through lhe evaporator. The lemperature and absolute
pressure of the refrigerant stay constant, but the enthalpy increases from left to
right. The pressure is at the compressor suction (LP) level.

. At point O, low-pressure superheated vapor reaches the compressor suction

inlet.

. Between points O and O, the compressor compresses the vapor, causing the
absolute pressure of the refrigerant lo rise, and its enthalpy to also rise.

. At point O, high-pressure superheated vapor is expelled from the compressor

discharge outlet.
 REFRTGERATTON COMPOTVENTS FART lt)
AND ENTHALPY DIAGRAM
. At point 6, the discharged vapor reaches the condenser inlet, and a new
refrigeration cycle begins.

PBs.,/Enth.b, tx.tqrd trr

I

Pressure/Enthalpy Diagram - R134a

10.0

,:
o
It
6

o6
c,
f
o
o
c
o
,o
l)
{to

HEAT OF
couPREssloN

250 n5 3S
I
I hthalpv ftrke)
I

Figure 4-'10. Pressure/enthalpy diagram for the R-134a (metric units).

NRE, Heat of Compression, and Coefficient of Performance

lmportantcharacteristics of a refrigeration system are:the net refrigeration effect, the

heat of compression, and the coefficient of performance. These properties can be
determined graphically by using the system's refrigeration cycle (refer to
Figure 4-10.)

. The net refrigeration effect (N.R.E.) is the enthalpy removed by evaporation' lt is

determined by drawing vertical lines downward from points @ and O. The
REFRTGERATTON COMPOTVENTS ?ART tD
AND ENTHALPY DIAGRAM
d ifference on the enthalpy (horizontal) axis where the lines cross this axis is equal
to the N.R.E.

. The heat of compression is the enthalpy added to the vapor, mainly by the work
done by the compressor. lt is determined by drawing vertical lines downward from
points O and 19. The difference on the enthalpy (horizontal) axis where the lines
cross this axis is equal to the heat of compression.

. The coefficient of performance (COP) is a pure number indicating the efficiency

ofthe refrigeration cycle. lt corresponds to the ratio ofthe enthalpy removed by
evaporation (N.E.R.) to the enthalpy added to the vapor during the compressing
phase. ln equalion form:

Net refrigeration effect (kJ,ks orBtu/bm)

Coefficient of performance =
Heat of compression {kJ,rs or Bru/tbm)

The higher the coefficient of performance, the better the efficiency of the system.

The COP of refrigeration syslems varies according to the conditions under which
they operate and the components constituting them. Therefore, this figure should
not be used to compare the performance of two refrigeration systems that operate
under differing conditions and/or that are not entirely made up of the same
componenls.
 Job Sheet
REFRTGERATION COMPOTVE TTS (PART l0
AND ENTHALPY DIAGRAM

OBJECTIVE

In this job, you will learn how to observe the system temperatures and pressures
over lime at various points of the system, using the Trend Recorder of the LVHVAC
software. You willthen use an enthalpytable to determine the values required to plot
the refrigeration cycle ofthe system. You will then observe the refrigeration cycle of
the system and measure the coefficient of performance, using a Pressure/Enthalpy
diagram.

EQUIPMENT REQUIRED

Lab-Volt Refrigeration Training System, Model 3431

PROCEDURE

Observing the System Temperatures and Pressures Over Time

! 1. On the control panel of the Refrigeration Training System, make sure the
main POWER switch is set to OFF (O).

Connect the Refrigeration Training System to the computer used to run the
LVHVAC software, via a USB cable. Turn on the computer and then run the
LVHVAC software.

! 2. Activate the Trend Recorder of the LVHVAC softlvare: in the menu bar of
this software, select the Iools menu, and then select the Trend Recorder
option. This will bring up the Trend Recorder, as Figure 4-1 '1 shows (without
the signals displayed in this figure, since the recorder has not been started
vet):

- Locate the section General of the Settings panel in the right section of
the Trend Recorder. Set the Sca/e (min) field of this section to 30. This
sets the displaytime (range ofobservation ofthe variables)ofthe Trend
Recorder to 30 minutes.
 REFRIGERATTON COMPOTVEMS PART I0
AND ENTHALPY DIAGRAM
Locate the section Data of lhe Settings panel in the right section of the
Trend Recorder. Select the following variables only (deselect the other
variables if they are selected):

. Pressure 1;
. Pressure 2;
. Temperature 3;
. Temperature 7;
. Compressor Current.

ln the menu bar of the Trend Recorder, select Acquisition, and then
Start to start the display of the selected variables.

FL VH Acqj'$o H.lp

> ll r g€
psrg .F A
l$ e,o- fo- a-l
TN POIUER la- E-l
UrP FEl/) E
NO 130 8,0 - NORTAL HEAT C0rient Tim (min) 46,!8

210 u0 ?,0 -
LOAD
Cursor Po5ition
l*
(min) f---

lg, m 6,0 -
ctur Descrhtion VaIrc Unit
t.x) 70 5,0 - Pr6.sc I --
i /"y'n
107,5 pJiS
Pr6we 2 I 8, 56 prll
ta 50 d0- -I Presrue 3 pstg
Tompa.hJo I - oF

m n 3'0 V1,/---------------.- J --1r--t-B lflpr.turc 2 oF

"' ]
Tof,psahrr.3 30,:4 ot:
l
d) l0 2,0- i Tcmpaafurc 4
CURRENT Tempryatui8 5 oF

n .10 1,0 _ __4

I
Iemp*Eture 6
-.--.-=-----------lZ Tempdoturc ? {1,?5 eF
0 .I} o,o' Curfft 2,3 A
33 vdtag€ - \t
Elfectiva Feor - w
Time (nir)
a

Figure 4-'t'1. Trend Recorder of the LVHVAC software displaying the selected variables as a
function of time.

tr 3. On the Refrigeration Training System, make the following settings:

Note: Do not tum on the Refrigeration Training Sysfem for now.

COMPRESSORSwitch ... OFF(O)

EVAPORATOR-FANSPEEDcontrolknob. ... HtcH
CONDENSER-FAN SPEEDcontrolknob. ..... Hatf of H|GH
HEAT LOAD switch . OFF (O)
Thermostatsetpoint .....5"C(41.F)
Manually-operated valves
V1 . . . . . . . . Open (handleturnedfullycounterclockwise)
V2... ....Closed(handleturnedfullyclockwise)
V3... ....Closed(handleturnedfullyclockwise)
 REFRTGERATTON COMPONENTS PART t0
AND ENTHALPY DIAGRAM

tr4. Turn on the Refrigeration Training System, then turn on the compressor. Let
the system run for about 20 minutes.

!5. On the Trend Recorder, examine the signal of Temperature 3 (temperature

at the evaporator outlet), and fill in the following sentences.

lmmediately after power up, the temperature sensed by the thermal bulb of
the TEV at the evaporator outlet is (higher/lower) than the
thermostat setpoint of 5"C (41'F). This causes the opening of the
thermostatic expansion valve (TEV) to be maximum to allow the full
refrigerant flow to enter the evaporator. As a result, Temperature 3
(increases/decreases).

As the evaporator cools down, the TEV opening is reduced to decrease the
flow of refrigerant entering the evaporator, causing Temperature 3 to
(increase/decrease). As more refrigerant is allowed into the
evaporator, the superheat sensed by the TEV sensing bulb
(increases/decreases). This causes the TEV opening to
(increase/decrease), causing the superheat to increase. This phenomena
can repeat, cyclically or not, untilthermal equilibrium is reached.

n 6. (Refer to the recorded signals). While Temperature 3 varies, does

Temperature 7 (temperature in the cooling chamber) slowly decrease in a
steady way until it becomes close to the thermostat setpoint of 5'C (41 'F),
causing the compressor to stop?

nYes trNo

n 7. (Refer to the recorded signals). When the compressor stops,

Temperatures 3 and 7 both start to (increase/decrease) in a
steady way. Once Temperature 7 has risen by a certain amount, the
compressor restarts to begin a new cycle.

tr 8. Leave the Trend Recorder open for the rest of the exercise, but minimize
this window. You should now see the Refrigeration Diagram of the
LVHVAC software.

Determining Refrigerant Enthalpy at Different Pressures and Temperatures

tr 9. Figure 4-12 shows an example of the temperatures and pressures that can
be read at the various test points of the Refrigeration Diagram, under the
current operating cond itions.

RE F RI G ERAT I O N TRAI N I NG S YSTEM

REFRTGERATION COMPONEVTS ?ART t0
AND ENTHALPY DIAGRAM
Using the temperatures and pressures indicated in Figure 4-12, fill in
Table 4-1-once complete, this table contains all the data required to plot
the refrigeration cycle of the system.

- ln the first (leftmost) column, record the gauge pressures indicated at

PS1 and PS2 of Figure 4-12. Conved these pressures into absolute
pressures and record your results in the second column.

- ln the third column, record the temperatures indicated at T1 through T5

of Figure 4-'12.

- ln the fourth and fifth columns, record the enthalpy corresponding lo

each recorded temperature (T1 through T5), according to the enthalpy
table for the R134-a in Appendix D of this manual.

GAUGE ABSOLUTE TEMPERATURE ENTHALPY (kJ/kg or Btu/lbm)

PRESSURE PRESSURE ('c/'F)
(barg/psig) (ba. abs./psia) Ltouto VAPOR

HP side HP side: T1:

(PS1):
T4:

T5:

LP side LP side: T2.

(PS2):
T3;
* To be completed later

Table 4-1. Pressu.e, temperature, and enthalpy data required to plot the refrigeration cycle.
 REFRTGERATTON COMPOTVENTS PART il)
AND ENTHALPY DIAGRAM

{,t_r
@
0.9 barg
ail
-1..7 0C
14 psig 28.7 0F
H \, _-z
-
@oC
12.3
e3"F J.

,
i
PI ta

I
46.4 "F

;
,
.-I
@
0.9 barg
14 Dsiq ^
(r) GI
6.8 rg ba

o""'n

eil
37.A aC
99.3 0F
-il
21.3 .C
70.0 "F

o@o
r23V 2.3A 185 W
-L2s,6 "c
78.0'F

Figure 4.12. Example ofthe temperatures and pressures that can be read atthe various test points
ot the system.

n 10. According to the data recorded in Table 4-'1, the temperature of the high-
pressure liquid refrigerant is at a minimum at test point
(T1lT4lT5). At that point, the enthalpy of the refrigerant is
(minimum/maximum), the refrigerant being
(superheated/subcooled) when it reaches the inlet of the expansion device.

\
 REFRIGERATTON COM?OTVE VTS ?ART t0
AND ENTHALPY DIAGRAM
Conversely, the temperature of the low-pressure vapor refrigerant is
maximum at test point (T2lT3). At that point, the enthalpy of
the refrigerant is (minimum/maximum), the refrigerant being
(superheated/subcooled) at the evaporator outlet.

Observing the Refrigeration Cycte and Measuring the Coefficient of

Performance

n 11. ln the LVHVAC software, locate the Refrigeration Training System panel
to the right of the Refrigeration Diagram. The System lnformation section
of this panelallows you to enterthe current settings of the system. Enterthe
current temperature controller setpoint, and the settings of the fan speeds
and heat load.

Now locate the Temperature Test Points section of the Refrigeration

Training System panel, as Figure 4-13 shows. This section indicates the
current temperature, absolute pressure, and enthalpy at test points Tl
through T5 of the Refrigeration Diagram. This data is continuously
refreshed.

$qq 6e g ooooo s
e.rng-mua'-l R.,*Fffi Trhg Srtm
E
tritpd rE
t#..effi04..
",'j'l
-pea G-e) r ill
Try&@robr
*rd.({) r* s L "rrr=,
[o Sg.Gd
f nronrmot
GD
'il f- sr..d
=t
rp,rl
lr a)

I
E
r ('.) P (b.r) H(tl/tq) l
il :':t tj: :irr I ffmp.
r2
t:,
l. :
: -:
tt!
: ii ;{:: ! resr
B
Ir
15
iir.
rr.a
al.
::- li:l J eonns
s$'lEd(t) 7,.
(mpr6tloR*h 4.23
uR.IriC.renffet(lJ/tq) lS.$
ldcd wnk dcrytu GJ/kq) s.Zr-
dfl R*. o, RcliiFd (tg./r) 0.61r
R.fdF*bo tryt, (lw) s r:
aarfi(EilortEr'm(e S.:39
RdcdHREiGtu*rh.Cdd;ns(H) tlzji
v& Floi R*. ot th. fryE.or (m!/mh)
.b
2J l.(
Vol, dot r*! olRdri$ * thc [ve. O(lGt (mr,/dn)
RGfrIg. trRt torr ry wd d th. lU, rt! (l!rtg)
?.gffi
:.sU
s2.67

o@o
r2l! llA lsii! t-__--.
@
27.2 "C

Figure 4-13. Sysfem lnformation and Temperature Test Poinfs sections of the Refrigeration
Training System panel.
 REFRTGERATTON COMPONE VTS qART il)
AND ENTHALPY DIAGRAM

tr 12. While the compressor is running, make the following observations in the
Temperature lest Polnfs section of the Refrigeration Training System
panel.

. The pressures at T1, T4, and T5 are equal. They correspond to the
absolute pressure on the HP side of the system.
. The pressures at T2 and T3 are approximately equal. They correspond
to the absolute pressure on the LP side of the system.

tr13 ln the menu bar of the LVHVAC software, select the lools menu, and then
click on Options..., which will bring up the Opfions dialog box. Make sure the
Display the Cycle /cons check box is selected, and then click OK to close
the Opfions dialog box.

! 14. Activate the Pressure/Enthalpy Diagram of the LVHVAC software. To do

this, click on this window's tab, as Figure 4-14 shows.

The Pressure/Enthalpy Diagram shows the refrigeration cycle of the

system, plotted by using the temperatures and absolute pressures at T'1
through T5 of the system (as displayed in the Temperature Iesf Pornfs
section of the Refrigeration Training System panel).

The display of the refrigeration cycle is continuously refreshed to reflect any

changes that may occur in the measured temperatures and pressures.

R E F RI G ERAT I O N T RAI N I NG S YSIEM

 REFRIGERATTON COM?O,wE VTS qART r0
AND ENTHALPY DIAGRAM
TAB TO CUCK

r.*6rr|,ipru.9-l
R.ffgpr* TrD. R-!3t
Pressure/Enthalpy Diagram - R-1 34a l*Rry. Cryto&.
s.tD.f* G*g) To,
Tc.iF&rc Co.tola
s.tD.ht ('f) l-s
Evry&i
tr sF.d I'D -l
Cqdcrs
Fn so..d l'@-_l
llqt Load

10.0
HP€IDE Pc l*--
I ("C) P (bar) H (kJ,/ks)
G TI 2i,i3 a.0: 2x1.Ba
t2 -11 84 l.8t 237.88
T3 -5.11 1,89 395.57

b
f4 60,1{ 8,0? 426,11

o LP€IDE T5 12,19 Lm 42!.16

sup€rhc.t('{) 6,J
Compr6ri0 Ratlo 4.Il
il.t (kJ,/kg)
Refrige.ntion Er.(t 157.69
td.C wdk of Cnlprcr.lon (kllkg) 3 L 1 i
flo, Rate of Rehi{rd.ot (IO/t) 0,60::J
R.frigeratio, C.paity (krv) 94 97
(@lncic.* ofPdfo]m.ne 5.(159
Ratc ofHedt Reifttion.t thc ffidenrer (klv) 109,90
Yol. Flo* R.t. ofth. Compre!.s (mr/'riln) 3 0102
VoL Hoe nate o[ Refrb, at thd Evap. &*lct (m,/ntn) 3.0 102
Rcfrig. trh(t tor. by wrk of thc EsF D.vke (k],/kq) 52,93

lm t25 lro t?5 N n5 lu n5 3(I, w 350 rr5 l(I} eJ 1fi 05

I I I
I EIflmlpy ftJ/kg) I I
I I

HEAT OF
COHPRESS!ON

F-
I

Figure 4-14. Pressure/Enthalpy Diagram with normal heat load when the TEV is used.

! 15. Allow the compressor to stop, then wait until it restarts to begin a new cycle.
3 minutes later, print the Pressure/Enthalpy Diagram and Refrigeration
Training System panel.

REF RI G ERATI O N T RAI N I NG S YS TE'T'

 REFRTGERATTON COMPOTENrS PART il)
AND ENTHALPY DIAGRAM
n 16. Determine the net refrigeration effect (N.E.R.) graphically on your printed
diagram. To do so, draw vertical lines downward from points I and @ until
they cross the enthalpy (horizontal) axis, as shown in Figure 4-14. The
difference on the enthalpy axis where the lines cross this axis is equal to
the N.R.E. Record your result below.

Compare your result to the value displayed in the field Net Refrigeration
Effect of the System Pertormance section on your printed Refrigeration
Training System panel. Are these values approximately equal?

EYes trNo

tr 17. Determine the heat of compression graphically on your printed diagram.

To do so, draw vertical lines downward from points 0 and @ untilthey cross
the enthalpy (horizontal) axis, as shown in Figure 4-14. The difference on
the enthalpy axis where the lines cross this axis is equal to the heat of
compression. Record your result below.

Compare your result to the value displayed in the field ldeal Work of
Compression of the Sysfem Performance section on your printed
Refrigeration Training System panel. Are these values approximately
equal?

E Yes trNo

tr 18. Based on the N.E.R. and heat of compression obtained in the previous
steps, calculate the coefficient of performance of the system. Record your
result.

Net refrigeration effect,*r/ks or Bru/tbm)

Coefficient of performance =
Heat of compression (kJ/ks or Bru/tbm)

REF RI G ERATIO N TRAI N I NG S YS TEM

R E F RtG ERATT O N COM POTVENTS qART t t)
AND ENTHALPY DIAGRAM
Compare your result to the value displayed in the field Coefficient of
Peiormance of the System Performance section on your printed
Refrigeration Training System panel. Are these values approximately
equal?

!Yes nNo

tr 19. Turn off the trainer and clos6the LVHVAC software.

Date:

lnstructor's approval:
 lnformation
Job Sheet
,{
ELECTRICAL CONTROL OF REFRIGERATION SYSTEI'S

lntroduction

Refrigeration systems require electricity to operate. Consequently, it is important to

know the basic principles of electricity and electrical control when working on these
systems.

Basic Principles

Electricity is a form of energy used for lighting, heating, or providing control and
power to do work. lt is produced by the flow of tiny particles of matter called
electrons through a conducting material. Examples of conducting materials are iron,
copper, and aluminum.

Electrical components such as wires, lamps, solenoids, fan motors, thermostats, and
electronic transmitters all use conducting material, and so allow electrons to pass
through them. To produce a flow of electrons, the electrical components must be
connected to a source of electromotive force that pushes the electrons through the
components. This source may be either a generator or a battery. For example,
Figure 5-1 shows a battery pushing electrons through electrical wires to energize the
solenoid of a solenoid valve. As a result, a magnetic field is created around the
solenoid.

<- OOO

'T;""_
Figure 5-1. Simple electrical circuit.

The electromotive force exerted by a source is called voltage. The magnitude of the
voltage is measured in volts (V). The instrument used to measure voltage is called
a voltmeter.

There is always an opposition to the flow of electrons through an electrical

component. This opposition to electron flow is called resistance. Resistance is
measured in ohms (a). The instrument used to measure resistance is called an
ohmmeter.
ELECTRICAL CONTROL OF REFRIGERAT'ON SYSIEMS

The result of electrons flowing through an electrical component is called current.

The magnitude of the currenl is measured in amperes (A). One ampere is equal to
the motion of6.24 x 1018 electrons past a cross section in 1 second. The instrument
used to measure current is called an ammeter.

Types of Electric Current

Current flow through an electrical circuit may be one of two types: direct current or
alternating cunent.

. Direct current (DC) is the type of current produced by batteries and dc power
supplies: the direction of the electric charges remains constant. Figure 5-2 (a)
shows the symbol used to represent a DC power source in electrical diagrams.
The current, l, flows by convention from the positive, or hot (+) terminal of the
source lowards the negative, or common (-) terminal.

I ^r
l+ \
T)
| \--l'
' ')

t______* GBOUNDED
WIRE

=
(CONNECTED
TO EARTH)
OV

(a) DC power source (b) AC power sourco

Figure 5-2. Symbols used to represent Dc and Ac power sources in electrical diagrams.

. Alternating current (AC) is the type of current supplied to most houses and
businesses: the electric charges varies in a cyclicai way, as opposed to
DC current. Although DC current was the first type developed by Thomas Edison,
AC cu rrent was proved to be much less expensive lo transmit over long distances
by Serbian scientist Nikola Tesla, after what was called the "War of Currents",
and is therefore more commonly used.

Figure 5-2 (b) shows the symbols used to represent an AC power source in
electrical diagrams. The flow of cunent in an AC circuit continuously reverses
itself, flowing from the line (L, or hot side) terminal towards the neutral (N, or
common) side, and vice-versa. However, the convention used is the same as for
DC circuits: the current flows from the L side to the N side.
ELECTRICAL CONTROL OF REFRIGERAT'O'V SYSTEMS

For safety purposes, it is a common practice to connect the low-voltage side of

an AC circuit to the earth. The voltage ofthe earth is 0 V. This practice is called
grounding. As Figure 5-2 (b) shows, lhe wire connecting the N (low-voltage side)
of the power source to the earth is called the grounded wire. The grounded wire
is the green conductor in the US (or green-yellow conductor in Europe and Asia)
of the line power cord.

Ohm's Law

Ohm's law states that the magnitude of the current flowing through an electrical
component is equal to the voltage drop across lhe component divided by the
resistance of the component:

Voltaoe dropM
(^,
Current...
Resistance (o)

Reformulated to calculate the voltage drop:

VoltagedropM = Resistance(o) x Currentlel

Or to calculate the resistance:

Voltage dropu)
Resistance (o)
Current 11y

ln Figure 5-1 , for example, if the resistance of the solenoid is 10 O, and the current
flowing through the solenoid is 2 A, the voltage drop across the solenoid will be 20 V.

Electrical Power

The capability of an electrical source lo move electrons through a circuit is called

electrical power.

DC circuits

ln DC voltage circuits, electrical power is measured in watts (W). The amount of

power generated by the electrical source is equal to the voltage supplied by the
source multiplied by the current drawn by the circuit. ln equation form:

Power* = Voltage M x Current 6y

Part of the electrical power generated by the source is dissipated as heat by each
component in the circuit, due to the resistance, or opposition to the current flow, of
the components. Usually, most of the power is consumed by an electrical device
called a load to perform a useful work such as producing light (lamp), providing
rotary motion (motor), moving a plunger (solenoid), etc.

The amount of power consumed by a load is equal to the voltage drop across this
load, multiplied by the current flowing through it. (lt is also equal to the square of the

REF RI G E RAT I O N T RA I N I N G S YSTE'U

ELECTRICAL CONTROL OF REFRIGERAT'O'V SYSTEMS

current flowing through the load, multiplied by the resistance ofthe load.) ln equation
form:

Consumed power@ = Voltagedrop, x Current 1n1

lf, for example, the voltage drop across the solenoid in Figure 5-1 is 10 V, and the
current flowing through the solenoid is 2 A, then the power consumed by the
solenoid will be 20 W.

AC circuits

ln AC voltage circuits, not all the power generated by the AC source goes to the
load. Part of this power returns to the source, due to the inductive and capacitive
components of the circuit. The power returning to the source is called reactive
power. Reactive power is measured in volts-amperes (VAR).

The power actually consumed by the load is equal to the product ofthe voltage and
the current produced by the source, multiplied by a power factor. That portion of
power is called true, or real power, and is measured in watts (W).

The power factor is usually expressed as a pure number comprised between 0

and 1. lf, for example, the power factor is 0.7, then 70% of the power golng to the
load will be consumed by the load.

True power, in watts, can be measured by using a wattmeter.

Closed and Open Circuits

Figure 5-3 shows a simple AC circuit used to power a compressor motor. This circuit
includes a 120-(2201240-\ V AC source, a POWER switch with normally open (NO)
contacl, a pressure switch with normally closed (NC), contact and a compressor. The
POWER switch allows an operator to make lhe cunent flow through the circuit or to
stop it. The pressure swilch is used for safety: its NC contact allows the current to
flow to the compressor as long as the circuit pressure stays within the pressure
range allowed by the culin and cut-out settings of the pressure controller.

. When the operator actuates the POWER switch [Figure 5-3 (a)1, this switch
contact goes from open to closed. Since the pressure-switch contact is also
closed, a complete conducting path is established, starting at the line (L) terminal
of the source, through the switches and lhe compressor motor, back to the
neutral (N) terminal of the source. As a result, the circuit is in the closed
condition, and a currenl flows through the circuit. Consequently, the compressor
motor is running.

. When the operator returns the POWER switch to the normal (deactuated) state
lFigure 5-3 (b)1, this switch contact goes from closed to open. This breaks the
continuity of the conducting path at the POWER SWITCH. As a result, the circuit
is in an open condition, and the current can no longer flow through the circuit.
Consequently, the compressor motor is off. The same thing would occur if, for
example, the pressure-switch contact were to go closed to open due to a circuit
pressure reaching the cut-in or cut-out setting of lhe pressure controller.
 ELECTRICAL CONTROL OF REFRIG ERATION SYSTEMS

POWER SWITCH
IN NORMAL STATE

PRESSURE
.^. SWITCH
120
(230) VAC \
SOURCE ') COMPRESSOH
'----/ MOTOR
RUNNING

(a) Closed circuit (b) Open circuit

Figure 5-3. A simple AC circuit used to power a compressor motor.

Measuring voltage, resistance, and current

As previously mentioned, voltage is measured with a voltmeter, resistance is

measured with an ohmmeter, and current is measured with an ammeter. These
meters are available as separate units, but they are usually found combined in a
single enclosure called a multimeter.

Figure 5-4 shows how to measure voltage drop, current, and resistance in an
AC circuit.

. To measure the voltage drop across a component, connect a voltmeter or

multimeter set to measure AC volts across the component terminals, as
Figure 5-a (a) shows. Then turn on the source.

. To measure the current flowing through a component, make sure the power
source is turned off, then connect an ammeter or multimeter placed in ammeter
mode in series with the component, as Figure 5-4 (b) shows. Then, turn on the
power source.

REF RIG ERATI O N TRAI N I NG S YSTEM

E LECT RI CA L C O N T RO L O F REF RI G E RAT I O,il S YS TEI'S

POWER SWITCH
ACTUATED

3 VOLTMETER

(a) Measuring voltage across the compressor

3
(b) Measuring current drawn by the compressor

(c) Measuring compressor resistance

Figure 54. Measuring voltage, resistance, and current in an AC circuit.

ELECTRICAL CONTROL OF REFRIGERAT'O'V SYSTEMS

Note: Serles means that all the current will llow through the component
and the rest of the circuit when the power source is turned on.

. To measure the resistance of a component, make sure the power source lS

TURNED OFF, then disconnect the component from the circuit. This may require
you to open one or more circuit connections. Connect an ohmmeter or multimeter
placed in ohmmeter mode across the component terminals, as Figure 5-4 (c)
shows. The ohmmeter has its own inlemal power source (battery) that supplies
a current used to test the resistance of the component.

Resistance measurements are often used to test the electrical continuity of a

component. When the resistance of a component is very high or infinite (- Q), the
component is said to be open. When the resistance is null, the component is said
to be shorted (0 O).

CAUTION!

Never measure resistance in a circuitrYhile the power source is turned on.

Failure to observe this rule may cause permanent damage to the meter'

Series and Parallel Circuits

A series circuit consists of electrical components that are all connected in series,
as Figure 5-5 (a) shows:

. The total resistance of the circuit, Rr, seen by the source, is equal to the sum of
the resistances of each circuit component.

. The current flowing through the circuit is equal to the source voltage divided by
the total resistance.

. Whenever a circuit component is open (of infinite resistance), no current will flow
through the circuit. The source voltage will be present across the open
component.

A parallel circuit consists of electrical components that are parallel, or branch

connected. Figure 5-5 (b) shows a simple parallel circuit:

. The voltage across each branch is equal to the source voltage.

. Each branch has its own resistance. The total resistance, Rr, seen bythe source
is equal to or lower than that of the branch of lowest resistance.

. The current flowing through the circuit is equal to the source voltage divided by
the total, or equivalent circuit resistance.

. Whenever a component in a branch is open, the source voltage will be present

across the open component.
 ELECTRICAL CONTROL OF REFRI GERATIO N SYSTEMS

v = 120 (230) VAC

r20 (230) vAc

RI = 7.4A
(a) Series circuit

v = 120 (230) VAC v = 120 (230) VAC v = 120 (230) VAC

o2a
"3[?EB.
120 (230) vAC

a
^
CoMPRESSOR
MOTOR
soo ,31["

a3=75O

Rr=5'8O
(b) Parallel circuit

Figure 5-5. Series and parallel circuits.

Electrical control circuits are usually a combination of parallel and series branches,
like the circuit used to control the Refrigeration Training system, shown in
Figure 5-6:

' Each separate branch is used to control the turning on or turning off of a specific
device independently.

' When the HEAT LOAD switch is actuated, the heat source becomes energized.
However, this does not affect the solenoid valve, the evaporator fan, or the
compressor motor in the other branches.
 ELECTRICAL CONTROL OF REFRIGERATION SYSTEMS

. When the speed of the evaporator or condenser fan is varied, using the
associated SPEED CONTROL knob, the voltage across the fan changes.
However, the voltage across the heat source, solenoid valve, or compressor
motor does not change.
ELECTRONIC
PRESSURE
CONTROLLEB

CoMPBESSOR
Y
--a/o--------------s4
THERMOSTAT

COMPRESSOB

SOLENOID EVAPOBATOR CONDENSER

VALVE FAN FAN

ll
t-o/o--l
COMPRESSOFI
(22O t 24OVAC
MOOELS ONLY)

Figure 5-6. Electrical control panel of the Refrigeration Training System.

Safety Rules

Working on electrical equipment requires that you observe the necessary

precautions, due to the possibility of electric shocks and/or damage to the
equipment. Motor circuits, for example, may carry very high currents that can cause
severe electric shocks. Even small currents may be dangerous under certain
conditions.

ln fact, the higher the circuit voltage, the higher the current that can flow through
the human body and, therefore, the greater the possibility for a severe or fatal
shock. The risk is increased when working in a wet room, or on components that are
damp and not insulated.

a. Never connect or disconnect electrical leads or components while the electrical

power source is ON.

b. When performing voltage or current measurements, the test leads or probes of

the multimeter, voltmeter, or ammeter should have a protective covering over
their ends to avoid the risk of short circuits and electric shocks, since these
measurements require that the electrical power source be on.

REF RI G ERAT I O N TRAI N I NG SYSTEM

ELECTRICAL CONTROL OF REFRIGERATION SYSTEMS

c. To increase your protection against electric shocks, always use screwdrivers,

wrenches, or pliers that have insulated handles. Moreover, use rubber gloves, /
i
rubber-sole shoes, or rubber boots.

d. Never leave any electrical lead unconnected. This may cause you to receive an
electric shock when you touch the unconnected end of a lead while the electrical
power source is on. This may also cause a short circuit to occur when the
unconnected end of a lead touches a metal surface.

e. All parts of a refrigeration system that can cause electric shocks must be properly
grounded. For example, the ground (green wire of the electrical power cord) is
normally connected to the ground wire of the motor compressor.
 Job Sheet
ELECTRICAL CONTROL OF REFRIGERAI'O'V SYSIEMS

OBJECTIVE

ln this job, you will learn the safety rules to follow when performing resistance and
voltage measurements in an electrical circuit. You will first perform continuity tests
on the thermostat of the training system. You will then measure the individual
resistance of the main system components that use electricity to operate. Finally, you
will perform voltage measurements across these components. This will allow you to
see how an electrical circuit composed of parallel and series branches operates.

EQUIPMENT REQUIRED

Lab-Volt Refrigeration Training System, Model 3431

PROCEDURE

Measuring Resistance

tr '1. On the control panel of the Refrigeration Training System, make sure lhe
main POWER switch is set to OFF (O).

Connect the Refrigeration Training System to the computer used to run the
LVHVAC software, via a USB cable. Turn on lhe computer and then run the
LVHVAC software.

! 2. On the Refrigeration Training System, make the following settings:

COMPRESSOR switch . . ...

OFF(O)
EVAPORATOR-FAN SPEED control knob ......... OFF
CONDENSER-FAN SPEED control knob .......... OFF
HEAT LOAD switch . . ...... OFF(O)
Thermostat setpoint ..... 5"C(41 'F)
Manually-operated valves
. . Open (handle turned fully counterclockwise)
v2 ...... Closed (handle turned fully clockwise)
V3 ...... Closed (handle turned fully clockwise)

n 3. Do not turn on the Refrigeration Training System for now.

ELECTRICAL CONTROL OF REFRIGERATION SYSIEMS

Th e rm ostat El e ctrical C o nti n u ity

tr 4. As Figure 5-7 shows, remove the thermostat cover by loosening the

thermostat screw and observe its internal construction:

. The thermostat is connected, via a capillary tube, to a temperature

sensing bulb located in the cooling chamber. lt has an adjustment knob
that allows you to adjust the setpoint (desired temperature in the
chamber).

. The thermostat features a single-pole, doublethrow (SPDT) switch.

This switch has a pole that switches back and forth between a normally-
open (NO)and a normally-closed (NC) contact.

. When the temperature sensed by the bulb rises up to the adjusted

setpoint, the SPDT switch becomes actuated, causing the switch
NO contact to go from open to closed, and the NC contact to go from
closed to open.

On the training system, only the NO contact of the SPDT switch is used.

COOLING CHAMBER

SETPOINT ADJUSTMENT KNOB

*- BULB

CAPILLARY
TUBE

*''t its; ---o

LJ ---o
J.--
polr
I

LOOSEN SCREW

Figure 5-7. Thermostat internal construction.

tr 5. Referring to Figure 5-8, connect an ohmmeter (or multimeter set to read

ohms) to the NO contact of the thermostat switch: connect one of the meter
test leads to the uppermost screw terminal (NO contact) of the thermostat,
and the other test lead to the lowermost screw terminal (switch pole).
ELECTRICAL CONTROL OF REFRIGERATION SYSTEMS

CAUTION!

Never connect an ohmmeter or multimeter set in ohmmeter

mode into a circuit while the power source is on. Failure to
observe this rule may cause permanent damage to the meter.

Figure 5{. Ohmmeter connection for testing electrical continuity.

a. Observe that the ohmmeter reads a null resistance (0 O approximately),

indicating that the NO contact is (open/closed). This
occurs because the cooling chamber is at room temperature, and is
therefore (above/below) the thermostat setpoint of 5'C
(41'F). Consequently, there is a (complete/broken)
conducting path for the current to flow to the SOLENOID VALVE (see
the electrical control diagram at the bottom of the trainer front panel).

b. While keeping the ohmmeter test leads connected to the NO contact of

the thermostat switch, increase the thermostat setpoint by turning its
adjustment knob fully counterclockwise, and listen for a click from the
thermostat as you do this. The click occurs when the setpoint
adjustment becomes (equal to/above/below) the room
temperature, causing the NO contact of the thermostat to go from
(open to closed/closed to open). This is indicated by the
ohmmeter, which now reads a (null/high) resistance.
Consequently, the conducting path for the current to flow to the solenoid
valve is now (broken/complete).

Note: An infinite resistance is indicated by a "1" or a "*" sign on

the ohmmeter display.

R EF RI G ERAT I O N TRAI N I NG S YSTEM

ELECTRICAL CONTROL OF REFRIGERAT'O'V SYSTEMS

! 6. Disconnect the multimeter test leads and reinstall the cover of the
thermostat, taking care not to damage the capillary tube. Leave the
thermostat adjustment knob lurned fully counterclockwise, in order for its
NO contact to be open.

lndividual Resistance of the Main Circuit Components

n 7. Look atthe electrical controldiagram atthe bottom of the trainer front panel.
at the POWER SWITCH, the conducting path is currently
(complete/broken ), since this switch is set to OFF (O);

the branch of the heat source is cunently (open/closed)

at the HEAT LOAD switch, since this switch is set to OFF (O);

- the branch of the solenoid valve is currently _ (open/closed)

at the THERMOSTAT switch, since the NO contact of the thermostat is
open;

- the branch of the evaporator fan motor is currently

(open/closed) at the SPEED CONTROL knob, since this knob switch is
set to OFF (O).

- at the COMPRESSOR switch, the conducting path is

currently
(complete/broken), since this switch is set to OFF (O).

- finally, the branch of the condenser fan motor is currently

(open/closed) at the SPEED CONTROL knob, since this knob switch is
set to OFF (O).

tr 8. Since, under the current configuration of the circuit switches, there is no

electrical connection belween the parallel branches of the circuit, the
individual resistance of lhe main component in each branch can be
measured independently.

Measure the resistance of the components listed in Table 5-1 by connecting

the ohmmeter to the proper banana jacks (TP) of the electrical control
diagram of the trainer. Record your results in the table.
 ELECTRICAL CONTROL OF REFRIGERATIO'V SYSTEMS

APPROXIMATE RESISTANGE MEASURED

COMPONENT RESISTANCE
120 VAC 220t240VAC

Solenoid valve (resistance between TP3 and =200O =635O

TP2)

Evaporator fan motor (resistance between 111 O

=340
TP4 andTP2)

Condenser fan motor (resistance between 211 o

=50C)
TP6 and TP2)

Compressor motor winding (resistance = 4A =7.5O

(sEE FrRsr NorE)
between TP5 and TP2)

Heat source (resistance between TP1 and = 12o- =390

TP2; tseesecoNDNorE)

Note: /f the operating voltage is 220/240 VAC, set the

COMPRESS OR switch to ON Q before measuring the resistance
of the compressor rnofor winding, and then return it to OFF (O).

Note: Io measure the resistance of the heat source, set the

HEAT LOAD switch to ON (l).Assume the resistance of this
switch to be approximately null (= 0 A). DO NOT turn on the
Refrigeration sysfem.

Table 5-1. Measuring the resistance of the main circuit components.

tr 9. According to the results recorded in Table 5-1, which circuit component

offers the highest resistance to the flow of current? The lowest resistance?

tr 10. With the ohmmeter connected to TP1 andTP2, make sure the HEAT LOAD
switch and COMPRESSOR switch are both set to the OFF (O) position to
open the branch of the heat source.

On the thermostat, turn the setpoint adjustment knob fully clockwise, which
will cause its NO contact to go from open to closed. The ohmmeter now
indicates the resistance of the branch of the solenoid valve (about 200 O at
120 VAC, or 635 Q a12201240 VAC).

set the HEAT LOAD switch to ON (l) to close the branch of the heat source,
and therefore connect this branch in parallel with that of the solenoid valve.

RE F RIG ERAT I O N T RAI N I NG S YSIEM

E L ECT R I C A L C O N T RO L O F R E F RI G E RAT'O'V S YS IE'I'S

Observe thatthis causes the ohmmeter reading to fall drastically to the heat-
source resistance of approximately 7 A al 120 VAC (or 39 O at
2201240 VAC). This occurs because when two or more branches are
electrically connected, the total, or equivalent resistance of the branches is
(equal to or lower than/higher than)that of the branch of
lowesl resislance.

n 11 . Disconnect the ohmmeter from the trainer.

Set the HEAT LOAD switch to OFF (O). On the thermostat, leave the
setpoint adjustment knob turned fully clockwise.

Voltage Measurements

! 12. Set the POWER switch of the trainer to ON (l). Do not lurn on the
compressor for now.

CAUTION!

With the power source turned on, an AC voltage of around

120 (22012401V isnow present at the various bananajacks of
the electrical diagram at the bottom ofthe trainer front panel.
To avoid the risk of electric shock, be careful not to touch
theseiacks. Do not connecl or disconnect electrical leads or
components to/from the jacks. Follow the manipulations
below in the stated order to perform voltage measurements.

CAUTIONI

The test leads of the voltmeter you are using should have a
protective covering over their ends to avoid the risk of short
circuits and electric shocks. lf not, make sure to connect the
test leads of the voltmeter to the positive (+) and
common (COM) terminals ofthe voltmeter first, then connect
the other ends ofthe leads to the indicated test points. Never
touch the metal parts of leads that are uncovered while or
after connecting the test leads,

! 13. Get a voltmeter (or multimeter set to read volts) and set it to read AC volts.
Connect the voltmeter across the AC power source terminals:

- Connect the positive (+)terminalof the voltmeterto TP1 of the electrical

control diagram, using a test lead.

- Connect the common lerminal of the voltmeter to TP2 of the electrical

control diagram, using a test lead.
ELECTRICAL CONTROL OF REFRIGERAT'ON SYSTEMS

Record below the voltmeter reading. This is the RMS source voltage.

Source vollage: = VAC

tr 14. Since the temperature in the cooling chamberis above the cunent setpoint
of the thermostat, the NO contact of the thermostat is closed, so that a
complete conducting path allows the current to flow through the branch of
the solenoid valve.

As Figure 5-9 shows, touch the screw of the casing of the valve solenoid
with the metallic blade of a screwdriver. Observe that the blade is attracted
to the screw, indicating that the valve solenoid is magnetized and, therefore,
that a current is flowing through the solenoid. ls this your observation?

!Yes trNo

SoLENOTO
SECTION

SCREWI)ruVER
BLADE

Figure 5-9. The blade of the scrcwdriver is attracted by the magnetized valve solenoid

! 15. With the voltmeter still connected across the source terminals (TP1 and
TP2), set the HEAT LOAD switch to ON (l) to allow the current to flow
through the branch of the heat source: this will turn on a light bulb in the
cooling chamber.

Observe that the voltmeter still reads the source voltage of around 120
(220124o\YAC, even if an additional branch is now powered by this source.
ls this your observation?

nYes trNo

! 16. With the voltmeter connected across the source terminals (TP1 and TP2),
set the EVAPORATOR-FAN SPEED control knob to HIGH to allow the
current to flow through the branch of the evaporator fan motor.
ELECTRICAL CONTROL OF REFRIGERAT'O'V SYSTEMS

Observe that the voltmeter still reads the source voltage of around 120
(2201240t VAC, even if three branches are now powered by the source.

This occurs because, when additional (series/parallel)

branches are connected lo a source voltage, the voltage across each
branch stays the same.

a 17. Set the CONDENSER-FAN SPEED control knob to HIGH, then set the
COMPRESSOR switch to ON (l).

Again, observe that the voltage across TP1 and TP2 is still around the
source voltage of 120 (2201240\ VAC, even if two parallel branches have
been added to the circuit. ls this your observation?

nYes trNo

n 18. Connect the voltmeter across the evaporalor fan motor:

- Leave the common terminal of the voltmeter connecled to TP2 of the

electrical control diagram.

- Connect the positive (+) terminal of the voltmeter to TP4 (+ side of the
evaporator-fan motor), using a test lead.

Slowly turn the EVAPORATOR-FAN SPEED control knob fully clockwise to

decrease the fan speed to a minimum. While doing this, observe that the
voltage across the molor (increases/decreases/stays the
same).

Note: Ihe EVAPORATOR-FAN SPEED control knob provides

electronic control of the fan speed.

! 19. Set the EVAPORATOR-FAN SPEED control knob to HlcH.

tr 20. Connect the voltmeter across the compressor motor:

- Leave lhe common terminal of the voltmeter connected to TP2 of the

electrical control diagram.

- Connect the positive (+) terminal of the voltmeter to TPs (+ side of the
compressor motor), using a test lead.

Record below the voltage drop across the compressor motor while it is
runnrng.

Voltage drop across compressor motor: = VAC

ELECTRICAL CONTROL OF REFRIGERATIO'V SYSTEMS

Then, set the COMPRESSOR switch to OFF (O). What happens to the
voltage drop across the compressor motor? Explain why by referring to the
electrical control diagram.

n 21. Set the COMPRESSOR switch to ON (l). Record in the space below the
current flowing through the compressor-under the current system
configuration, as indicated by test point A of the LVHVAC software just
below the compressor icon.

Current flowing through the compressor: A

D 22. Given the voltage drop and the current recorded in the previous steps, and
a power factor of 0.66, calculate the theoretical amount of power consumed
by the compressor motor under the current system configuration.

Consumed powero) = Voltagedrop x Current 1ry

x 0.66
",

Your result should be approximately the same as the real power value
indicated by test point P of the LVHVAC software. Are they the same?

trYes !No

n 23. Disconnect the voltmeter from the trainer.

n 24. On the trainer front panel, set the COMPRESSOR switch and HEAT LOAD
switch to the OFF (O) position.

Turn off the trainer by setting the POWER switch to OFF (O).

n 25. Close the LVHVAC software.

Name: Date:

lnstructor's approval :

RE F RI G ERATI O N TRAI N I NG S YSTEM

 PRESSURE AND TEMPERATURE CONTROL
I N REF RI G E RAT'OA' S YS TE'}'S

Pressure Controllers

Pressure controllers are used in refrigeration systems for safety and pressure
control. They sense pressure and switch the compressor on or off when the desired
pressure (setpoint) is reached by breaking a conducting path in the electrical control
circuitry.

Pressure controllers come in two different types:the low-pressure type, and the high-
pressure type.

. The low-pressure controller is found on the low-pressure (suction or LP) side

ofthe refrigeration system. lt maintains the pressure on the LP side ofthe system
below the level required to ensure efficient vaporization of the liquid refrigerant
within the evaporator.

At the same time, the low-pressure controller provides safety control against
pulling vacuums, thereby preventing damage to the compressor. Moreover, by
controlling the LP-side pressure, the low-pressure controller can also be used
to control the temperature in the cooling chamber. This occurs bemuse changes
in the evaporator temperature result in changes in lhe suction pressure. A
thermostat maytherefore be unnecessarywhen the low-pressure controller starts
and stops the compressor at the desired temperatures and pressures.

Finally, the low-pressure controller can also prevenl the formation of ice on the
evaporator.

. The high-pressure controller is found on the high-pressure (discharge or HP)

side of the refrigeration system. lt is used mainly for safety purposes: it prevenls
the pressure on the HP side from becoming excessively high, thereby preventing
rupture of components in the system.

At the same time, the high-pressure controller maintains the pressure on lhe
HP side to the level required to ensure efflcient condensation of the gaseous
refrigerant within the condenser.

Pressure controllers often use a bellows or a Bourdon tube as the pressure

sensing element. These elements expand or contracl as the sensed pressure varies.
When the pressure reaches the setpoint, an electrical contacl is mechanically closed
or open to make or break a conducting path in the electrical control circuitry.
PRESSURE AND TEMPERATURE CONTROL
I N R E F R I G E RAI'O'V S YS TE'US

The Electronic Pressure Controller of the Refrigeration Training System

This controller, shown in Figure 6-1, can acl as either a low- or high-pressure
controller, depending on lhe pressure range (user adjustable) and on the type of
transducer used. As the figure shows, the controller mainly consists of a pressure
transducer, and an LCD display with touchpad.

- The pressure transducer produces a DC voltage proportional to the sensed

pressure. The sensed pressure appears on the LCD display, in psig, and is
refreshed every two seconds.

- When the sensed pressure reaches the cut-in or cut-out setpoints, an internal
relay with SPDT contacts becomes actuated, shifting its NO and NC contacts to
their opposite state. A stalus LED on the front face of the controller indicates
whether the relay is energized (LED is on) or deenergized (LED is off).

- The 3-button touchpad allows the user to adjust the cut-in and cut-out
setpoints.
. The Cut-ln setpoint (cil) sets the pressure (in psig)atwhich the intemalrelay
of the controller is energized.

. The Cut-Out setpoint (col)sets the pressure (in psig) at which the internal
relay of lhe controller is de-energized.

lsecondary setpoints (ci2 and co2) are also available, but they are unused for the
control of the Refrigeration Training System.l

- Once cil and col have been adjusted, the conlroller automatically selects the
necessary mode of control. The selected mode is indicated on the LCD display:
ooen-Hioh ooen-towfl
ffi or

PRI ARY
SETPOINTS

TRANSDUCER

SENSED
(GAUGE) oPE .t-ow
PRESSURE CONTROL
ODE

HARNESS

Figu.e 6-'1. The elect.onic pressure controller of the Refrigeration Training System.
 PRESSURE AND TEMPERATURE CONTROL
IN REFRIGERAT'O'V SYSTEMS
The pressure controller has three selectable ranges for the cut-in and cut-out
setpoints. This range is factory setto 0-100 psig (0-6.9 barg). Given this range and
the type of pressure transducer used on the system, the controller will automatically
select the Open-low mode and therefore acl as a low-pressure controller.

Operation

Figure 6-2 shows the operation of the controller when cil and col are adjusted to
30 psig (2.'l barg) and 10 psig (0.69 barg), respectively.

. The controller stops the compressor if the pressure on the LP side reaches the
cut-out point of 10 psig (0.69 barg).

. The LP-side pressure is then allowed to rise to the cut-in point of 30 psig
(2.1 barg): at that point, the controller restarts the compressor.

. The LP-side pressure is then allowed to decrease lo the cutout point, and so on.

100 psig
(6.9 barg)

LED IS ON

I
30 p6ig CUT-IN (cil) COMPRESSOH RESTARTS
I
(2.1 ba€)
I

SETPOINT LED ON OB OFF

DIFFEHENTIAL

'10 psig
I CUT-OUT (col ) COMPRESSOR STOPS
(0.69 barg)

I
LEO IS OFF

0 psis
(0 bars)

Figure 6.2. Operation ofthe electronic pressure controller in the open-low mode, with cil and col
set to 30 psig (2.1 barg) and 10 psig (0.69 barg), respectively.

Thermostal Controllers

Temperature controllers, orthermostats, are used in refrigeration systems for safety

and temperature control. They sense temperalure and switch a device, such as a
compressor or a solenoid valve, on or off when the desired temperature (setpoint)
is reached.
PRESSURE AND TEMPERATURE CONTROL
I N REF RI G E RAT'O'V SYS IEMS

Figure 6-3, for example, shows a lhermostat ofthe fluid pressure type similar to that
used on the Refrigeration Training System. The thermostat mainly consists of a
thermal bulb, an SPDT switch, and a setpoint adjustmenl knob with dial.

. The thermal bulb is used as the temperature sensing element. lt is linked to the
thermostat via a capillary tube. The bulb is usually mounled on the evaporator
side or in the cooling chamber.

The bulb is filled with refrigerant, and is therefore sensitive to temperature

changes. As the temperature of the refrigerant changes at the bulb, a bellows
expands or contracts accordingly, acting on the SPDT switch, through a
mechanical link.

. The setpoint adjustment knob permits adjustment of the setpoint (desired

temperalure in the chamber) on a calibrated dial.

BULB
^-
DIFFERENTIAL
AIUUST ENT
RANGE } SCALE
ADJUSTiIENT
DI,AL -'z
ELECTRICAL
CONNECTIONS
TO SPDT
SIVTICH

Figure 6-3. lnternal construction of a thermostat.

Operation

Assume that the NO contact ofthe thermostat SPDT switch is used. As long as the
temperature sensed by the bulb is above the setpoint, the switch is actuated, causing
its NO contact to be closed. This makes a conducting path in the electrical control
circuit.

Once the temperature has decreased lo the adjusted setpoint, the NO contact opens
to break the conducting path in the electrical control circuit. The temperature in the
cooling chamber then increases by a certain amount before lhe NO contacl closes
again to re-make the eleclrical circuit.
 PRESSURE AND TEMPERATURE CONTROL
I N REF RI G ERAT'O'V S YS TEMS

The difference between the adjusted setpoint and the temperature at which the
NO contact closes to re-make the conducting path is called the differential. A
differential is required to prevent the NO contact from oscillating between the closed
and open conditions when the temperature is around the setpoint.

The differential is fixed on some models, while adjustable on others. The thermostat
shown in Figure 6-3, for example, has an adjustable differential which can be set by
sliding a lever along a scale plate.

Solenoid Valves

Solenoid valves are used in refrigeration systems to control the flow of liquid
refrigerant to the evaporator. The solenoid valve is installed in the liquid line
upstream of the expansion (metering) device. The intended purpose is to prevent
liquid refrigerant from flowing to the evaporator when the desired temperature is
reached.

Solenoid valves are also used in multi-chamber systems to permit independent

control of the temperature in each chamber. ln large refrigeration systems, they
permit the control of several evaporator sections, as the heat load varies.

Figure 6-4 shows a cross-section view of a direct-operated, two-way solenoid valve

similar to that used on the Refrigeration Training System. The valve is fully closed
(non-passing)when the solenoid is de-energized, and fully open (passing) when the
solenoid is energized.

. When a current flows through the solenoid, a plunger is attracted toward the
center ofthe valve solenoid. This shifts the valve to the open condition, allowing
the refrigerant to flow to the evaporator. A minimum pressure drop is required
across the valve lo keep the valve in the open condition.

. When the current flow to the solenoid is intenupted, the solenoid becomes de-
energized. This causes a spring and the weight of the plunger to force lhe valve
stem against the valve seat, shifting the valve in the closed condition. This stops
the flow of refrigerant to the evaporator.
PRESSURE AND TEMPERATURE CONTROL
I N REF RI G E RAT'O'V S YSTEMS

--'r--

INLET

RE OVABLE

SOLENOIO

PLUNGER

VALVE SEAT

CUTdWAY VIEW

Figure 6-4. cross-section view of a direct.operated, two.way solenoid valve.

A thermostat normally controls the flow of current to the valve solenoid to keep the
temperature in the cooling chamber around the setpoint, as Figure 6-5 shows.

. When the adlusted setpoint is lower than the temperature sensed in the cooling
chamber, the thermostat NO contacl is closed to energize the solenoid of the
valve. The valve is in the open condition, allowing the refrigerant to flow to the
evaporator in order to produce a decrease in the temperature of the cooling
chamber.

. When the temperature in the cooling chamber has decreased to the thermostat
setpoint, the thermostat NO contact opens to de-energize the solenoid valve. This
shifts the valve to the closed condition, thereby stopping the flow of refrigerant to
lhe evaporalor. The compressor will continue to run until the low-pressure
setpoint of the pressure controller is reached, causing the compressor to slop.
 PRESSURE AND TEMPERATURE CONTROL
IN REFRIGERAT'ON SYSIEMS

{
THERTIIAL
BULB
/'---------\ _ _ _
I

rHERirosrAr 1#)
V
LOW+RESSURE
CONTROLLER

6)l
I
I
,

I
Figure 6-5. Schematic diagram of a simple refrigeration system.
 PRESSURE AND TEMPERATURE CONTROL
IN REFRIGERATIO'V SYSTEMS

OBJECTIVE

ln this job, you will study the operation of the pressure controller of the training
system, while the thermostat is off-circuit. You will modify the cut-in and cut-out
pressures of the controller, and observe the effect that this modification has on the
operation of the compressor and on the temperature in the cooling chamber. You will
then return the pressure controller to the default (factory) settings and study the
operation of the thermostat, fortwo different temperature differentials. This will allow
you to see the interaction that occurs between the thermostat, solenoid valve, and
compressor operation.

EQUIPMENT REQUIRED

Lab-Volt Refrigeration Training System, Model 3431

PROCEDURE

Operation of the Pressure Controller for Two Different Setpoint Differentials

tr 1. On the control panel of the Refrigeration Training System, make sure the
main POWER switch is set to OFF (O).

Connect the Refrigeration Training System to the computer used to run the
LVHVAC software, via a USB cable. Turn on the computer and then run the
LVHVAC software.

! 2. On the Refrigeration Training System, make the following settings:

COMPRESSORSwitch ..... OFF(O)

EVAPORATOR-FANSPEEDcontrolknob. ... HlcH
CONDENSER-FAN SPEED control knob . Half of HIGH
HEAT LOAD switch . . OFF (O)
Thermostat setpoint
Adjustmentknob. ..... Turnedfullyclockwise
(thermostat off-circuit)
Manually-operated valves
V1 . . . Closed (handle turned fully clockwise)
V2 . . . . . . Open (handleturned fullycounterclockwise)
V3 . . . Closed (handle turned fully clockwise)

tr 3. Turn on the Refrigeration system. Do not turn on the compressor for now.
PRESSURE AND TEMPERATURE CONTROL
I N REFRIGERAT'ON SYSTEMS

! 4. On the pressure controller, sel the culin and culout setpoints to 30 psig
(2.1 barg) and 20 psig (1.4 barg), respectively. To do so, perform the steps
below.

a. Press the MenulGlbutton once, which will cause the LCD to indicate
lj|
a flashing ci1 (cut-in setpoint 1).

b. Press the Menrffi brtton on"e again. The current pressure setpoint
l_vt
for ci'l is displayed. lf this value is not 30, set it to 30 (psig) by using the
up and Down rrro* buttons, then press the ttzenu Uutton
S S
once to save the value. The display lhen returns to the pressure
currently sensed by the pressure transducer.

Nolei The display automatically returns to the sensed pressure

display after 30 seconds of inactivity.

c. Press lhe Menu Ortton once. Then press the Uf arrow

@ S
button once, which will cause the LCD to indicate a flashing col (cut-
out setpoint 1).

d. Press the Men, ffi brtton on"e again. The cunent pressure setpoint
lj|
for co1 is displayed. Set this value to 20 (psig) using the Up and Down
,rro* orttons, then press the Mrrr$ urtton once to save the
$
value. The display then returns to the pressure currently sensed by the
pressure transducer.

tr 5. On the LCD of lhe pressure controller, observe that the switch icon is
I
displayed, indicating that the controller is in the (Open-
High/Open-Low) mode of control and, therefore, that it will operate as a
(highJlow-) pressure controller.

! 6. Note that a low-pitch sound (hum) is produced by the solenoid valve,

indicating that the solenoid is currently energized. This occurs because the
temperature in lhe cooling chamber is (above/below) the
thermostat setpoint, so that the NO contact of the thermostat switch is
_ (open/closed), allowing a current to flow to the valve solenoid.
 PRESSURE AND TEMPERATURE CONTROL
I N REF RI G E RAT I O N S YS TEMS

n 7. Activate the Trend Recorder of the LVHVAC software: in the menu bar of
this software, select the Iools menu, and then select the Trend Recorder
option, which will bring up the Trend Recorder.

ln the General section of the Trend Recorder's Seftings panel, set the
Scale (min) field of this section to 30.

ln the Dafa section of the Trend Recorder's Settings panel, select the
following variables (deselect the other variables if they are selected):

. Pressure 1 (HP-side pressure);

. Pressure 2 (LP-side pressure);
. Temperature 7;
. Compressor Voltage.

ln the menu bar of the Trend Recorder, select Acquisition, and then
Start to start the display of the selected variables.

tr8. Turn on the compressor, and wait for about 15 minutes to let the system
stabilize.

n9. Observe the signals on the Trend Recorder, as the compressor is cycled on
and off by the pressure controller (see Figure 6-6).

The compressor voltage falls to 0 V (compressor is turned off) once

Pressure 2 (LP-side pressure) has decreased to the (cut-
in/cut-out) setpoint of the controller.

Conversely, the compressor voltage rises to the AC line voltage of 120

(2201240) V (compressor is restarted)once Pressure 2 has re-increased to
the (cut-in/cut-out) setpoint of the controller.

REFRIG ERATION TRAI N I NG SYSTEM

PRESSURE AND TEMPERATURE CONTROL
I N REFRIGERATION SYSTEMS

FL !4!w A.qtton li.b

> ll ! E|€

135

currcnt Tlft (min)

r!) fursor State
Curror Porition (sin)
IU Scale (min)

ql
Vds trit
7.34 bdg
75 1.97 beg
' b*g
o
-.c
15
-.c
a)

8.7? oC

.11
0
0?

Figure 5-6. Trend Recorder display with with cil and col of the pressure controller set to 30 psig
(2.'l barg) and 20 psig (1.4 barg), respectively.

n 10. Print the Trend Recorder. Turn off the compressor.

n 11. On your printed Trend Recorder, measure the cut-in and cut-out setpoints,
and record your results below. Then, calculate and record the setpoint
differential.

Cut-in setpoint: barg/psig

Cut-out setpoint: barg/psig

Setpoint differential (cut-in setpoint cut-out setpoint):

barg/psig

! 12. On your printed Trend Recorder, observe the display of Temperature 7

(temperature in the cooling chamber) and Pressure 2 (LP-side pressure):

Once the system has stabilized, the temperature in the cooling chamber is
quite stable, in spite of the variations in pressure on the LP side of the
system. This occurs because the pressure controller currently operates as
(low-/high-) pressure controller.

REF RI G ERAT I O N T RAI N I NG SYS TEM

 PRESSURE AND TEMPERATURE CONTROL
IN REF RIGERAI'O'V SYSTEMS
Consequently, by controlling the pressure on the (LP/HP) side
of the system, the controller also controls the
(pressure/temperature) in the cooling chamber.

-
! '13. On the pressure controller, change the culin and cut-out setpointsto
30 psig (2.1 barg) and 15 psig ('1.0 barg), respectively. To do so, perform
lhe steps below:

a. Press the Menu lGI Sr,,on on"e, whichwill cause the LCD to indicate
l_52t
a flashing ci1 (cutin setpoint 1).

b. Press the Menrffi brtton on"e again. The cunent pressure setpoint
t_vl
for ci1 is displayed: 30 (psig). Keep it set to 30, then press lhe Menu
Ortton once to save the value. The display then returns to the
$
pressure currently sensed by the pressure transducer.

Nolei The display automatically returns lo the sensed pressure

display after 30 seconds of inactivity.

c. Press lhe Menu Urtton once. Then press the Un anow

$l f$
button once, which will cause lhe LCD to indicate a flashing col (cut
out setpoint 1).

d. Press the MenrS Ortton on"e again. The cunenl pressure selpoinl
for col
is displayed (20 psig). Set it to 15 (psig) by using the Up and
oown anow buttons, then press the fuenr., button once to
$ S
save the value. The display then returns to the pressure currently
sensed by the pressure transducer.

! 14. Turn on the compressor and wait for about 15 minutes to let the system
stabilize.

Observe the signals on the Trend Recorder, as the compressor is cycled on

and off by the pressure controller (see Figure 6-7).
 PRESSURE AND TEMPERATURE CONTROL
I N REF RIG ERATIO'V SYS TEM S

H. Viil Aqirrao iLh

> [ r Eg

Cuircnt Iime (min)

tm Ceror state
EurJor Porati,on (min)
10J Scale {min)

q)

75

d)

15

NEW , n
PRESSURE Ic-ulfl-
GoNTROLLER (.____
SETPOINT lcurou
\
DIFFERENTI,AL

Figure 6-7. Trend Recorder display with with ci1 and col of the pressure controller set to 30 psig
(2.1 barg) and '15 psig (1.0 barg), respectively.

tr 15. Print the Trend Recorder.

Then, turn off the compressor, but leave the trainer POWER switch set to
oN (l).

tr 16. On your printed Trend Recorder, measure the cut-in and cut-out setpoints,
and record your results below. Then, calculate and record the setpoint
differential.

Cutin setpoint: barg/psig

Cut-out setpoint: barg/psig

Setpoint differential (cut-in setpoint cut-out setpoint):

barg/psig

n 17. Compare the Trend Recorder previously obtained with the setpoint
differential of 0.7 barg (10 psig) to the one just printed for a setpoint
differential of 1 .1 barg (15 psig).

The cyclical variation in pressure on the LP side of the system (Pressure 2)

is of (higher/lower) amplitude with the higher setpoint
differential. As a result, you might observe that the temperature in the

REF RI G ERAT I O N TRAI N I NG SYSTEM

 PRESSURE AND TEMPERATURE CONTROL
I N REF RIGERATION S YSTEMS

cooling chamber is a bit (more/less) stable over time than with

the lower setpoint differential.

n 18. On the pressure controller, return the cut-in and cut-out setpoints to 30 psig
(2.1 barg) and 10 psig (0.7 barg), which are the default factory settings. To
do so, perform the steps below:

a. Press the nZenu button once, which will cause the LCD to indicate
$
a flashing cil (cut-in setpoint 1).

b. Press the lrZenuffi button once again. The current pressure setpoint
t-vt
for ci1 is displayed: 30 (psig). Keep it set to 30, then press the Menu
Ortton once to save the value. The display then returns to the
S
pressure currently sensed by the pressure transducer.

Note: Ihe display automatically returns to the sensed pressure

display after 30 seconds of inactivity.

c. Press the nzenu button once. Then press the tJp arrow
$l
button once, which will cause the LCD to indicate a flashing col (cut-
out setpoint 1).

d. Press the fUenu button once again. The current pressure setpoint
$
for co1 is displayed. Set it to 1 0 (psig) by using the U p andOown anowSl
buttons, then press the Menu$lOrtton once to save the value. The
display then returns to the pressure currently sensed by the pressure
transducer.

lnteraction Between the Thermostat, Solenoid Valve, and Compressor

Operation

tr 19. Turn off the trainer by setting the POWER switch to OFF (O).

Remove the thermostat cover by loosening the thermostat screw.

On the righthand side of the thermostat, locate the differential adjustment

lever and adjustment scale, as Figure 6-8 shows. Make sure the lever is set
to the MlN. position, which corresponds to the default factory setting. ln
this position, the setpoint differentia! (difference between the culin and
cut-out setpoints) is 1.7"C (3'F) approximately.
PRESSURE AND TEMPERATURE CONTROL
IN REFRIGERATION SYSTEMS

-)
I

I
-J
DIFFERENTIAL
ADJUSTTIENT
LEVER

Figure 6€. Thermostat differential adjustment lever.

tr 20. On the Refrigeration Training System, make the following adjustments:

COMPRESSORSwitch ..... OFF(O)

EVAPORATOR-FANSPEEDcontrolknob. ... HIGH
CONDENSER-FANSPEEDcontrolknob. .....LOW
HEAT LOAD switch .. . ON (l)
Thermostatsetpoint ...7.2"C(45'F)
Manually-operated valves
Vl . . . . . . . . Open (handleturned fullycounterclockwise)
V2... ....Closed(handleturnedfullyclockwise)
V3... ....Closed(handleturnedfullyclockwise)

! 21. Turn on the trainer by setting the POWER switch to ON (l). Then, turn on
the compressor.

Get a voltmeter (or multimeter set to read volts) and set it to read AC volts.
Connect the voltmeter across the solenoid valve terminals of the electrical
control diagram at the bottom of the trainer front panel:

Connectthe positive (+) terminalof the voltmeterto TP3 of the electrical

control diagram, using a test lead.

Connect the common (COM) terminal of the voltmeter to TP2 of the

electrical control diagram, using a test lead.
 PRESSURE AND TEMPERATURE CONTROL
I N REF RI G E RAT'ON S YS TEMS

WARNING!

With the power source turned on, an AC voltage of around

120 (22Ol24OlV is now present across the screw terminals of
the thermostat SPDT switch. Since the thermostat cover is
removed, be very careful not to touch the thermoslat screw
terminals to avoid the risk of eleciric shock. Do not connect
any leads or components to/from these terminals.

CAUTION!

The test leads of the voltmeter you are using should have a
protective covering over their ends to avoid the risk of short
circuits and electric shocks. lf not, make sure to connect the
test leads of the voltmeter to the positive (+) and
common (COM) terminals of the voltmeter first, then connect
the other ends ofthe leads tothe indicated test points. Never
touch the metal parts of leads that are uncovered while or
after connecting the test leads.

Z 22. Wail lor about 20 minutes to let the system stabilize.

n 23. Study the operation of the system over one cycle by observing the signals
displayed on the Trend Recorder and the voltmeter reading (Figure 6-9).

As long as the decreasing temperalure in the cooling chamber

(Temperature 7 on the Trend Recorder) is above the thermostat setpoint of
7 .2'C (45'F\, the NO contact of the thermostat switch is

(open/closed); lherefore, there is lnola 120 (2201240\-Vl

AC voltage across the terminals of the solenoid valve. As a result, the
solenoid valve is in the (passing/non-passing ) condition to
allow refrigerant to flow to the evaporator.

When the decreasing temperature in the cooling chamber becomes around

the thermostat setpoint, the NO contact of the thermostat switch
(opens/closes), so that the AC voltage across the valve
solenoid is (removed/applied). This causes the solenoid to
become (energized/de-energized), and the valve lo make a
weak click as it goes to the (passing/non-passing) condition.
Th iS (allows/stops) lhe refrigerant flow lo lhe evaporator, so
that bubbles can be seen through the sight glass of the moisture/liquid
indicator. Shortly afler that, the pressure on the LP side (Pressure 2) drops
rapidly to the 0.7-barg (1O-psig) (cut-in/cu!out) setpoint of
the low-pressure controller, causing the compressor lo
(restarustop). The temperature in the cooling chamber then starts to re-
increase, along with the pressure of the LP side.
 PRESSURE AND TEMPERATURE CONTROL
I N REFRIGERATION SYSTEMS

When the increasing temperature has risen by a certain amount equalto the
current thermostat (setpoinUdifferential) of about 3'C (5.4'F),
the solenoid of the valve is (re-energized/de-energized ),
causing the valve to make a loud click as it becomes
(passing/non-passing). The temperature in the cooling chamber continues
to increase, along with the pressure on the LP side. When this pressure
reaches the 2.1-barg (3O-psig) (cut-in/cut-out) setpoint of the
low-pressure controller, the compressor (restarts/stops),
causing the temperature in the cooling chamber to start
(increasing/decreasing) again to begin a new cycle.

Fa. td A(qrrtih H+
>t.Ag
fi
fwref,t Time (min) 58,1:
50

4
1)

a
I -

--l-
st*ur D6{rlptim Val! Unit
p Pr.r3urr I
V Prossrc2
T Prcrrue3
T Tffpdltuc I
T Tempa*uc2
T Tcfipa*w83
?,9? b$a
1.86 bdg
" b&g
.C

T TcmMdur. 4
SETPOINT T Tem.rature 5

PRESSURE I,CUUX
CONTROLLER J..--
o,r'r=J[3,11l. \au"r

Figure 6-9. lnteraction between the thermostat, solenoid valve, and compressor operation, with
the thermostat differential set to MlN.

n 24. Print the Trend Recorder and set it aside for now.

tr 25. Turn off the trainer by setting the POWER switch to OFF (O).

On the thermostat, set the differential adjustment lever halfway between the
"MlN" and "MAX" marks on the differential adjustment scale.

n 26. Turn on the trainer by setting the POWER switch to ON (l). Wait for about
15 minutes to let the system stabilize.
 PRESSURE AND TEMPERATURE CONTROL
I N REF RI GE RATI O N S YSTEMS

WARNING!

With the power source turned on, an AC voltage of around

120 (22012401V is now present across the screw terminals of
the thermostat SPDT switch. Since the thermostat cover is
removed, be very careful not to touch the thermostat screw
terminals to avoid the risk of electric shock, Do not connect
any leads or components to/from these terminals.

4 27. With the thermostat differential now set halfway between lhe MIN and MAx
settings, study the operation of the syslem over one cycle by observing the
signals displayed on the Trend Recorder and the voltmeter reading
(Figure 6-10).

Observe that the displayed signals and the interaction between the
thermostat, solenoid valve, and compressor operation are similar to when
the thermostat differential was set to a minimum.

However, note the followang difference: after the temperature in the cooling
chamber (Temperature 7) has reached the setpoint and lhe compressor has
stopped, the temperature in the cooling chamber must increase by a greater
amount before lhe valve solenoid is re-energized (i.e. before the valve
makes a loud click), due to the increased thermostat differential [bein9 now
around 7"C (12.6'F)1. ln fact, you might observe that the compressor
reslarts before Temperature 7 reaches the required level (thermostat
selpoint plus differential), due to the LP-side pressure reaching the culin
setpoint of the pressure controller beforehand. ln that case, a glitch (narrow
vertical bar due to the compressor being temporarily cycled on and off) will
appear in the compressor voltage.

Record your observation below, and explain.

R E F RI G ERAT I O N T RA I N I N G S YSIE/L'
PRESSURE AND TEMPERATURE CONTROL
I N REF RIG ERATI O N S YSTEMS

Fls t/hi, A(q.rrfin Hch

> lt ! gg

l8

l6
Curror State
fureor Pofition (min)
l/t

t2
Value Unat

Y Pr65@ 1 8,00 baq

.10. \_ 9 Pr6ue2
T PrE.@ 3
2,m
-
barg
bdc
T T6filps*ure 1 -oC
f l.fiper3l*c2 ..c
6 T TempardurE 3 't
T Temprrature { ,'c
T T.mpardlra 5 ..C
4 .oC
f TemFEr,*are 6
F Timperature 7
{. f (urent
P ',o[age
T Elfecta!. Fowr

Figure 6-10. lnteraction between the thermostat, solenoid valve, and compressor operation, with
the thermostat differential set to half of MAX.

n 28. Turn off the trainer by setting the POWER switch to OFF (O).

On the thermostat, set the differential to the minimum (factory) sefting

by placing the adjustment lever to the "MlN" mark on the adjustment scale.
Place the thermostat cover back into place and tighten the screw.

tr 29. Disconnect the voltmeter from the trainer.

u 30. On the trainerfront panel, setthe COMPRESSOR switch and HEAT LOAD
switch to the OFF (O) position.

tr 31. Close the LVHVAC software.

Name: Date:

lnstructor's approval:

REFRIG ERATION TRAI N I NG SYSTEM

 THERMOSTATIC EXPANSION VALVE ADJUSTMENT

lntroduction

Figure 7-'l shows a refrigeration cycle for the R134-a. Each point used to plot this
quadrilateral (in red) represents the refrigerant properties (pressure, temperature,
enthalpy) at a speciflc point of the cycle.

. Points of the quadrilateral that are located on horizontal lines (lines of constant
temperature) indicate that the refrigerant is a mixture of liquid and vapor.

. Points ofthe quadrilateral that are located on the saturated vapor curve indicate
that the refrigerant is at the boiling point, and that it has completely turned into
vapor.

Points ofthe quadrilateralthat are located to the right ofthe saturated vaporcurve
indicate that thermal energy has been added to the vapor: the vapor is said to be
superheated.

. Points of the quadrilateral that are located on the saturated liquid curve indicate
that the refrigerant is at the condensing point, and that it has completely turned
into liquid.

Points of the quadrilateral that are located to the left of the saturated liquid curve
indicate that thermal energy has been removed from the liquid: the liquid is said
to be subcooled.
 THERMOSTATIC EXPANSION VALVE ADJUSTMENT

AASOLUTE
PRESSURE
( Pa,.b..)

.l' /
I )ul\rnt I
jl
urrrrthtntic.rls
l
Ilsi ti('Ir:
10
HFC-134a ,i
s.
k fi \i/.
,I .-{l"'c
I Pressure-Enthalpy Diagram
(Sl Units)
",1'
t. U, ><)\
6 c)
t; 1R ?.,'?e
rl
4
i R
ll fl i\ i, 4cn-, cn
LIOUID
I SUBCOOLING

2
I li
li li
ti Ol
o,
,.
r<) o
I I
o I
o' I
ilfli I :li
1r
it t\ -:8o
-
70',--+
i (or0
I I I I ? o oro o c, I
t VAPOR
1 i II E. SUPERHEATING
t":
J!
0.8
0.6
ii, o
gF
o:.
lit
I
0.4 ii

o.2

0. I -o'
1l'l,l
o&o' .
iil,u
l--o ,' 6' -
li
I q ,!I (ol (o ,'.\ iij i; t'
,o ,.o
rl 1t+ rfi-l,*t:t-t-lrrtt 7r'f"- 1i
1 r-$
0.08 I' /l
a: '-r4Ll:lil'L^ili tll I
0.06
J- /l
v
ll

: l:: :::3:/: ffi

0.04

o.o2
l.
rr,o
q3 q
oooo ci
;
ot.
o ci; ,:
il 3: +ilti[!lJ]i
tlt
--l-L
r,Q ;- trrooal.,olJ.rok)ro t8 & o
?-rt:,
1t! rrt ffTfi-fifi
0.01
400 450

Figure 7-1. Vapor superheating and liquid subcooling.

 THERMOSTATIC EXPANSION VALVE ADJUSTMENT

Superheat

The saturated vapor normally becomes superheated nearthe end ofthe evaporator.
Before it leaves the evaporator, the superheated vapor continues to absorb thermal
energy: this ensures that liquid refrigerantwill not enterthe compressor suction inlet.

The superheat of the superheated vapor at a given point is equal to the difference
between the temperature of the vapor and the temperature at which the vapor
becomes saturated, for a given pressure.

The superheat of the vapor is usually measured by using the steps below (refer to
Figure 7 -2\:

. Firsl, measure the pressure of the superheated vapor at the evaporator outlet
(that is, where the sensing bulb ofthe thermostatic expansion valve is located);

. Then, find the saturation temperature corresponding to the measured pressure

on a pressure-temperature (P/T) chart;

. Finally, calculate the difference between the saluration temperature and the
temperature of the superheated vapor at the evaporator outlet. The result
corresponds to the superheat.

€.6rc (22.D
1.6 b.rg
lztt D,,tgl

OUILET
0'c (32'R -5.6'C (22"F)
1.6 barg 1.6 barg
(22.4 Fls) 122.1 rigl
5.6.C (ro.F)
SUPERHEAT

Figure 7.2. The pressure/temperature (PT) method of measuring sup€rheat.

Since there is usually no pressure port at the evaporator outlet, the pressure is often
measured at the compressor service valve instead. Therefore, in commercial units,
an additional value of 0.14 to 0.2barg (2or 3 psig) is usually added to the pressure
measured at lhe service valve, to take account of the pressure drop that occurs in
the refrigerant line between the evaporator outlet and the compressor suction inlet.

REFRIG ERATIO N TRAIN ING SYSTEM

THERMOSTATIC EXPANSION VALVE ADJUSTMENT

The measured superheat gives an indication of the efficiency of the evaporator coil.
For example, a high superheat can indicate thal the evaporator is operating very
inefficiently, because the refrigerant is vaporizing too quickly in the evaporator coil.
A high superheat can result in poor heat transfer in the cooling chamber. On the
other hand, a negative superheat value indicates that the refrigerant is not
completely vaporized at the evaporator outlet, which can cause liquid refrigerant to
reach the compressor suction inlet, and in turn can cause premature failure of the
compressor.

Table 7-1 indicates the recommended superheat for high-, medium-, and low-
temperalure refrigeration systems.

REFRIGERATION SYSTEM RECOMMENDED SUPERHEAT

High-temperature [-1.1 "C (30'F) and Between 5.5 and 6.6" ('10 and 12'F)
above in the evaporatorl approximately

Medium{emperature [between -1 6'C and Between 2.8 and 5.5'C (5 and 10 F)

(0'F and 30'F in the evaporator)l
-1.1 "C approximately

Low-temperature [below -16"C (0"F) in Between 1.1 and 2.8'C (2 and 5"F)
the evaporalor)l approximately

Table 7-1. Recommended superheat for high-, medium-, and low-temperature refrigeration
systems.

ln many refrigeration systems, the superheat can be adiusted by turning a screw on

the thermostatic expansion valve (TEV). Turning the screw in the clockwise direction
will increase the superheat. Turning the screw in the counterclockwise direction will
decrease the superheat.

Before measuring the superheat, the system should be allowed to run for around
15 minutes.

Subcooling

Subcooling is the removal of thermal energy from the refrigerant, after it has
completely turned into a saturated liquid.

Subcooling takes place in the condenser, and is dependent upon proper airflow in
lhe condenser, room temperature, and refrigerant pressure in the condenser.
Subcooling increases the efficiency of some refrigeration systems, the liquid
refrigeranl being cooled before it passes the metering device.

One method of subcooling a refrigerant is to run the liquid line and suction line
together. This method also serves to superheat the cool refrigerant in the suction line
to ensure that no liquid refrigerant enters the compressor suction inlet.
 TH ERM OSTA TIC EXPA'VS'ON VALVE ADJ U STM ENT

To measure subcooling, use the steps below:

. Measure the pressure of the liquid refrigerant as it leaves the condenser.

. Once the pressure of the liquid refrigerant has been measured at the condenser,
add 0.14 to 0.2 barg (2 or 3 psig) to the measured pressure to take account of the
friction in the liquid line and of the vertical rise.

. Find the saturation temperature corresponding to the resulting pressure on a

pressure-temperature chart.

. Convert the resulting pressure into the corresponding saturation temperature by

using a pressure-temperature (PT) chart.

. Finally, find the difference (in absolute value) between the saturation temperature
and the temperature at the evaporator inlet. The result corresponds to the
subcooling value.

RE F RI G ERATI O N TRAI N I NG SYSTEM

I *rr*,ur*n ,o* r*o,*,*n
"rrrr* |
6
 Job Sheet
THERMOSTATIC EXPANSION VALVE ADJUSTMENT

OBJECTIVE

ln this job, you will learn how to calculate superheat. You will then measure
superheat under differing heat loads with the thermostatic expansion valve (TEV)
adiusted to the default factory setting. Finally, you will modify the setting of the TEV
and see the effect that this has on the superheat.

EQUIPMENT REQUIRED

Lab-Volt Refrigeration Training System, Model 3431

PROCEDURE

Calculating Superheat

! 'l . Figure 7-3 shows an example of the temperatures and pressures that can
be displayed in the Refrigeration Diagram ofthe LVHVAC soflware. Using
this diagram, fill in Table 7-2.

- First, record the temperature at the evaporator outlet (as indicated at T3

of Figure 7-3).

- Then, record lhe pressure at the evaporator outlet (as indicated at PS3
of Figure 7-3).

- Referring toTable 7-3, find the saturation temperature corresponding to

the evaporator outlet pressure at PS3. Record your result in the third
row of the table.

Calculate the superheat (difference between the saturation temperature

and evaporator outlet temperature). Record your result in the table.

Given that the superheat of the Refrigeration Training System should be

around 6"C (11'F) when stable, is the calculated superheat (as recorded
in Table 7-2) too high?

trl Yes trNo

REFRIG ERATION IRA"V"VG SYSTEM

TH ERMOSTA TIC EXPAA'S'ON VALVE ADJ USTM ENT

TEMPERATURE AT THE EVAPORATOR OUTLET (T3)

PRESSURE AT THE EVAPORATOR OUTLET (PS3)

SATURATION TEMPERATURE CORRESPONDING TO THE

EVAPORATOR OUTLET PRESSURE

SUPERHEAT

TableT-2. Galculating the superheat for given temperature and pressure at the evaporator outlet.

REFRIGERANT TEMPERATURE REFRIGERANT PRESSURE

-17.6'C (0"F) 0.43 barg (6.3 psig)

-14.e'C (5'F) 0.61 barg (8.8 psig)

-12.1 "C (10'F) 0.80 barg (11.6 psig)

-6.6'C (20"F) 1.24 barg (18.0 psig)

1.1 'C (30"F) 1.77 barg (25.6 psig)

4.4"C (40'F) 2.38 barg (34.5 psig)

e.e'c (50"F) 3.10 barg (44.9 psig)

15.4"C (60"F) 3.92 barg (56.9 psig)

20.9'C (70'F) 4.88 barg (70.7 psig)

26.4'C (80'F) 5.96 barg (86.4 psig)

31.e'C (e0'F) 7.20 barg (104.2 psig)

37.4"C (100'F) 8.58 barg (124.3 psig)

42.9"C (110'F) 't0.13 barg (146.8 psig)

48.4"C (120'F) 11.86 barg (171.9 psig)

53.9'C (130'F) '13.8 barg (13.8 psig)

59.4'C (140'F) 15.91 barg (230.5 psig)

64.9'C (150"F) 18.24 barg (264.4 psig)

Table 7-3. R-134a pressure temperature (P/T) relationship.

 TH ERMO STATIC EXPA'VS ION VALVE ADJ USTMENT

@Iil
I 0.9 barg -1.7 oC I @
-12.3 0C

W
I 14 psig 28.7 oF 9.3 0F

en
8,3 0C

46.4 0F

--
@
0.9 barg
14 psig r---r
(,)
\-/
@
6.8 barg
ee psis
fl

.J
Iil
37.0 0c )
99.3 0F @
21.3 0C
53.4
ID 0C
70.0 0F

ooo 129.2 0F
=r
V
123 A 2.3 185 !V F-rJ-
2s.6 oc
-ID 78.0 0F

Figure 7-3. Example ofthe temperatures and pressures that can be measured atthe various test
points of the system.

Measuring Superheat Under Nominal and High neat l-oaUs with the
TEV-Factory Setting

tr 2. On the control panel of the Refrigeration Training System, make sure the
main POWER switch is set to OFF (O).
 THERMOSTATIC EXPANSION VALVE ADJUSTMENT

Connect the Refrigeration Training System to the computer used to run the
LVHVAC software, via a USB cable. Turn on the computer and then run the
LVHVAC software.

! On the thermostatic expansion valve, manually unscrew the cap of the

superheat adjustment screw by turning it in the counterclockwise direction,
as Figure 7-4 (a) shows. Set the screw cap aside for now.

CAUTIONI

It is not recommended that you use a wrench to remove the

cap of the adrustment screw. lf you must use a wrench to
loosen the cap, do it while holding the valve with another
wrench (or a pair of locking pliers) on the flare nut of its
bottom or evaporator port, as Figure 7-5 shows, to prevent
the valve from turning and damage to the tubing connected
to the valve.

(
(a) REI,TOVE CAP OF
SUPERHEAT ADJUS-T}?!ENT SCREW

TO
EVAPORATOR
INLET /

I
l.
UOJID INLET
.l

Figure 7.4. Remove the cap of the superheat adjustment screw and note the position (angle) of
the screw slit.
 THERMOSTA NC EXPA'VS'ON VALVE ADJ USTMENT

Set the screw cap aside for now. Carefully note the current adjustment
of the superheat adjustment screw: to do so, draw the screw slit in its
current position (angle) in Figure 7 -4 (b). This adjustment corresponds to the
TEV-factory setting.

Note: /f ls important here to carefully note the current adiustment

of the TEV screw, since you will have to set the screw back to the
factory sefting at the end of this exercise-

T
:V

ILLG
n.
rb-ro
d.F
Figure 7-5. When a wrench must be used to loosen the cap, do it while holding the valve with
another wrench on the flare nut of its bottom or evaporator port.
=
n 4. on the Refrigeration Training system, make the following settings:

COMPRESSORswitch ..... OFF(O)

EVAPORATOR-FANSPEEDcontrolknob- "' HIGH
CONDENSER-FAN SPEED control knob ' Half of HIGH
HEAT LOAD switch oFF (o)
Thermostat setPoint 2'C (35"F)
 THERMOSTA NC EXPANS'Oil VALVE ADJ USTMENT

Manually-operated valves
V1 . . . . . . . . Open (handleturned fullycounterclockwise)
V2... ....Closed(handleturnedfullyclockwise)
V3... ....Ctosed(handteturnedfullyclockwise)
on the pressure controller, change the cut-in and cut-out setpoints to
1 .7 barg (25 psig) and 0.4 barg (5 psig), respectivety.

n 5. Turn on the Refrigeration Training system, then turn on the compressor.

with the HEAT LOAD switch set to o, the system is operating under
nominal heat load (a single light butb on).

wait for about 15 minutes to let the system stabilize. Figures 7 -6 and r -7
show an example of the data and signals displayed in the LVHVAC software
with the nominal heat load.

Fh Ys Tdr frb
E 6e g ooooo E
ecft6crrtu mgaml R.fn! mton Tr.ari.9 *st.o c
E
RafiCm* tr,l
Lowfr6auraConuollar
*Fra {L.E)
TafrDarauro Cotrolls
*Fn(.O
*
@ail
ilfl
hr la.cd
0.7 barg -8.1 oC ID
-18
6 0C Cond..ts
hr SFd

GD
1.5 .C B

@
0.7 barg tutsrh.t(.c)
ir'l .D
7 .8 barg
fl.t R.tr!.r.tb E i.d (U/t!)
Id.rl hrt of (omrerb. (U/tC)
Fb{ tutc of turriq€r.lt (r!/r)
(r) R.fic..h (.tsdy &w)

6Er
oc g
42.8
r-E .P
r-----Er- L/.1
ooo
v
223 A I.7 253 W
@
25.2 .C

Figure 7'6. Refrigeration Diagram with nominal heat load and TEV adjusted to the
default-factory
sefting.

-
 T H ERM OS TA Trc EXPATVS'ON VALVE ADJ U ST M ENT

Trend Recorder
FilC /i!! AcquEitjn Lhb
ll I Eg
bers .c

18, 60 :-0- ls- o-l

IE=
E-l
E
Currcot fime (min) 152.9j
16, 50 :10 - corerstate lotr---l
Cursr Positbn (min)
t4. 40 :10 - s<ale (min) l:;l
t2 30 r80 - :

ffi. 7.1{ b.rg

t0 20 1J0 - II" - barg
0.81 brrg
8 t0 r20 -- II -oc

-j,
T A" "737 !C
6 0 90 -_
I -oc
-oc
{ -10 60- \ .oc
-2.05
t -?0 30 I .A
0 -30 0
1" 0.01 v

1:9 r38 lrl ll.l

Time (min)
!

Figure 7-7. Trend Recordersignals with nominal heat load and TEV adjusted to the default-factory
setting.

! 6. While the temperature in the cooling chamber (T7) is close to the 2'C
(35'F) setpoint and the superheat (indicated in the Sysfem Pefformance
section) is quite stable, note and record the following data:

a. Evaporator outlet temperature (T3):

b. Evaporator outlet pressure (PS3):

c. Cooling chamber temperature (T7):

d. Superheat:

n 7. Set the HEAT LOAD switch to I (ON). This will turn on the second light bulb
in the cooling chamber and, therefore, will increase the heat load.

Wait for about 15 minutes to let the system stabilize. Figures 7-8 and 7-9
show an example of the data and signals displayed in the LVHVAC software
with the increased (high) heat load.

REF RI G ERAT I O N T RAI N'A'G S YSIEM

 T H ERMOS TA N C EXPA'VS'O'V VALVE ADJ U STM ENT

B. i16' loolr Edp

qq 6e € ooooo ffi
Rchb.r.rbnDgr.m P.fr r.ilt o. ir.,. .! s"sr.r
I E
&.hi(trr.nt TE
Lor;&$r!* Co.hllar
*tFa.t (b.B) l:

Ta6par&ra Contrcilar
5.t eeo

@.il
t\ ,:tii -D
+,irt Eeaportor
f.o St cd
Condaatar
lGi
0,7 barg -5.3 oC -t79oc ;. f.r SF.d l'6--
I
@ti B
6---
15oc I T ('(l P (b.r)
r;!
rl :ii.
t2 :::l
; T4 62,39 3,69 {1?.t3
I T5 {1.19 t t9 {t0.{9
.l

I
B
fuFtu.t (.c) e.,
Comp6ra. ktb S.0l
n.t R6ig€r.t-. Efi.rl (E/Iq)
@
7.7 barg
l&.lworlofComFsn(Ulrs)
Iro.l:
)t.n
tue kt. dLhirr.nt (kg/r)

c
t.4!7i
Rchirr.tboc.Fcty(tw) l.td
Cetuorof hfrmBx. 5.S6
&t! orffit k cdbo at thc Coi&o.rr (k*) l.{6
ret rbx utr oIkft0.t th. Ey.p outLr (m! 0.039;
kfrt €ff.dL6r bvwdof th Etp k* (l sl.:l

ailn
oc
l9.l

ooo
V
222 A 1.7 251 W
.D
25.4 cC

Figure 7-8. Refrigeration Diagram with increased heat load and TEV adjusted to the default-factory
setting.
 TH ERMOSTA NC EXPANS'ON VALVE ADJ U STM ENT

sicr Acquisition lap W

ll I g€
v slttin0 s +x
bilq 'c iE= s-i
Is 60. ts- s-l
E
Current Tinre (mitr)
t6 50 ll0 - au15or state E;.
l1 10 :lo---***]
E
Cutsor Position (min)
5.ate (nrin) r-
hs3.o2

l: 30 r80-
I

Color :: Der(riptioo VBlue Unit

|
Fres!ore 1 7.!4 barg
t0 l0 lso- I

I Pressure 2 - barg
Pretsore 3 0.83 borg

10 1:0 --
--1
t
I
af TemFerature
Temperature 2
1

6 0 eo- I \
\---
-----+---- Temperature 3
Temperature 4
oc
5C

.t -10 oo-"-l I Tempernture 5

Temperature 6
ec

Teoperature 7
.:0 30- | Curent A
voltage
0 -30 o Effedive Power
1l:
-1. 1i6 1:9 r6J

Time (min)
l-1 1-.1

{ __ irl

Figure 7-9. Trend Recorder signals with increased heat load and TEV adjusted to the default-
factory setting.

n 8. While the superheat (indicated in the Sysfem Performance section) is quite

stable, note and record the following data:

a . Evaporator outlet temperature (T3):

b Evaporator outlet pressure (PS3):

c. Cooling chamber temperature (T7):

d. Superheat:

tr 9. Compare the superheat obtained with the nominal heat load (as recorded
in step 6) to the superheat obtained with the increased heat load (recorded
in the previous step).

Does the superheat stay approximatelythe same forboth loads [around 6"C
('10.8'F)1, demonstrating the ability of the TEV to compensate for the
variation in heat load through variation of its orifice opening? Explain.

REF RIG ERAT I O N TRAI N I NG SYSIEM

TH ERMOSTA NC EXPA'VS'ON VALVE ADJ USTMENT

tr 10. Leave the system set as it is, and keep it running. Proceed with the next
section.

Measuring Superheat Under High Heat Load with Modified TEV Setting

n 11. As Figure 7-10 shows, turn the superheat adjustment screw of the
thermostatic expansion valve 112 turn clockwise.

lEu

TURN % TURN CW

Figure 7-10. Turn the superheat adjustment screw ofthe TEV 112 turn clockwise.

tr 12. Wait for about 15 minutes to let the system stabilize. Figure 7-1 '1 shows an
example of the data displayed in the LVHVAC software with the increased
heat load.
 TH ERM OS TA N C EXPANS'O'V VALVE ADJ U STMENT

$a-_ 6iE € ooo'|oo s RetrEEdm Trilrg SysEm | {

Re{rlrratls Dlqril | 6

wa6u.@*
Brd* oa,

*Bn (t) l

@
1.2 barq
ED
0c
1.7
ltu ,m5 E
r{ t) l'(bd)
''frl

l? '{ !i

15 ') rl
o
!.t
r6tf,*r tdh
BR&Fctr*<r(b;kg) 160 5l
I&dwd d(ou6rh(kl,lq)
fhna.dn€l&d (19r.)
khE.hf,€at(l{, rff
r.#iikil dPalmd.. !.65:
t-. d h*kFtb A ft atu (H) ::i
Id tu H. d tJig- I lh b+ M {aP
rcts 6d tort b, 9d d tE tE |,cfrc(l

ID@@
L21V 2lA lslw
erf
)u2"c

Figure 7-11. Refrigeration Diagram with high heat load and modified TEV setting.

tr '13. While the superheat (indicated in the System Peiormance section) is quite
stable, note and record the following data:

a. Evaporator outlet temperature (T3):

b. Evaporator outlet pressure (PS3):

c. Cooling chamber temperature (T7):

d. Superheat:

tr - load with
14. Compare the data obtained for a high heat with the TEV-factory setting
(as recorded in step B) to the data obtained the new (current) TEV
setting (as recorded in steP 13).
TH E RM OSTA N C EXPA'VS'O'V VALVE ADJ U STM ENT

Since the adjustment screw of the TEV has been turned in the clockwise
direction, the superheat has (increased/decreased ).

,, -
".., " s:""Jffi l1ffi :lliiil ;:HJll,'ii"'="
*"*
Consequently, with the current TEV setting, the evaporator is operating

(quickly/slowly) in the evaporator coil. As a result, the temperature in the

cooling chamber is slightly (higher/lower) than it was with the
TEV factory setting.

tr 15. Set the TEV superheat adjustment screw back to the factory setting:

Turn the screw 1/2 turn counterclockwise in order for the position
(angle) of the screw slit to be the same as that recorded in
Figure 7-4 (b).

tr 16. Wait for about 15 minutes to let the system stabilize. Figure 7-12 shows an
example of the data displayed in the LVHVAC software when the TEV has
been properly readjusted to the default factory setting.

tr 17. while the superheat (indicated in the Sysfem Performance section) is quite
stable, note and record the following data:

a. Evaporator outlet temperature (T3):

b. Evaporator outlet pressure (PS3):

c. Cooling chamber temperature (T7):

d. Superheat:
 THERMOSTATIC EXPANSION VALVE ADJUSTMENT

sqlq 6lq g ooooo E

R.f.196.!ln DLsm I
R.6'Fao Tr-.p 5Fnrn I x

r*F.rr
.--.(r.a I -- -;;

cb @
--'|ih ED
+_* !in-a..r
h'.-.
r-h.
r
]'iol-l
--!
?

as.c -9.0.c f,o

E----
t@
5i c ry g
Il.L) t(br, R(u rc)

I 6
rGrr.(.4,

I
@
r I barq
(q*lib
$.,'r&k.Gliao
!d.Jft* i(c6i.lDtrd

e @t irbfi*lFdOro
rddGe.3.' G!r,

e EdMbfu.ortuOr,
dh.&rr..l...ll!4Brd(d
.dtr9|6Er*rdh.aEhG
:f,
..4r
r7-

.D
H
q
@
21 50C

GDGD@
t2r v 2l A 136 !'?
.ID

Figure 7-12. Refrigeration Diagram \rith high heat load and TEv-tactory setting.

E 18. Comparethe data obtained initially with the TEv-factory setting (as recorded
in step 8) to that recorded in the previous step. The data must be similar,
indicating that the TEV has been properly readjusted to the default factory
setting. lf so, replace the cap of its adiustment screw back into place and
tighten it manually.

CAUTION!

Do not use a wrench io tighten the cap of the valve

adlustment screw'

E 19. On the pressure controller, return the cut-in and cut-out setPoints to 2.1 barg
(30 psig) and 0.7 barg (10 psig), which are the default factory settings.

Set the COMPRESSOR switch and HEAT LOAD switch to the

OFF (O) position.
THERMOSTA TIC EXPANS'ON VALVE ADJ USTMENT

! 20. Close the LVHVAC software.

n 21. Based on the knowledge gained in this course, you should now be able to
complete the inspection report of the system that you began to fill out in Job
Sheet 1 (see Table 1-4). Complete the report (Table 74).

IDENTIFICATION

Technician name

Date

SYSTEM INFORMATION

Description

Model number

Serial number

Refrigerant type

Metering device type

Evaporator type

Condenser type

Thermostat Setpoint (typical)

Differential

Pressure controller Cut-in pressure

Cut-out pressure

ELECTRICAL DATA (TYPICAL)

Compressor v (vAC)
LRA (A)

RLA (A)

Evaporator fan v (vAc)

t(A)

Condenser fan v (vAC)

t(A)
 THERMOSTATIC EXPANSION VALVE ADJUSTMENT

OPERATIONAL INFORMATION (TYPICAL)

ldle pressures and temperature Compressor pressure

on LP side (PS2)

Compressor pressure
on HP side (PS1)

Ambienl temperature
(16)

Compressor running v (vAc)

with HEAT LOAD applied

| (A)

Pressures Low-pressure (PS2)

High-pressure (PS1)

Temperatures Cooling chamber (T7)

Condenser inlet (T5)

Across condenser
(r5 - r1)
Across evaporator
( r2l - lr3l )

Superheat

OBSERVATIONS

Table 7.4. lnspection report.

Name: Date:

lnstructor's approval:
 TROUBLESHOOTING

lntroduction

A fault in any part of a refrigeration system will usually show up as an unsatisfactory

temperature or operating condition.

Each system has its own characteristics. Consequently, lhe more familiar you are
with the system, the quicker and easier it is to find faults and correct the problem.

To keep track ofthe system conditions, ensure maximum performance, and detect
suspect or faulty operation, maintenance technicians perform regular inspections of
the equipment, where they mark down operation data in an inspection report.

lmportant conditions to know about a refrigeration system are

. the temperature of the evaporator and condenser during the operation cycle;

. the discharge pressure and suction pressure during the operation cycle.

The operating conditions are lhen compared to the designed conditions in the
system when a fault is suspected. A drastic variation in a system's temperature or
pressure from the designed conditions can indicate system malfunction.

The two basic principles employed as a guide for troubleshooting a fault are

. to observe the symptoms of the fault;

. asking questions concerning the malfunction.

These two principles are used by system manufaclurers to build troubleshooting

charts. These charts, which take the form of tables or diagrams, consist of step-by-
step observations and questions used to approach the problem and locate the fault
in a logical and systematic way.

Electrical Faults

Electrical faults are often the cause of refrigeration syslem breakdown. Many
electrical faults occur as a result of poor or corroded connections on components.
Some electrical faults are more obvious than others. These faults can usually be
found and repaired before any damage is caused, either to the system or chamber
being refrigerated. Examples of electrical faults are listed below.

R EF RIG E RAT I O N IRA'IV,,VG SYSIEM

TROUBLESHOOTING

Evaporator Fan and Associated Circuit Failure

A fault occurring in the evaporator fan and associaled circuit is usually indicated by
the fan blade not turning and decreased cooling in the cooling chamber. Since less
heat is absorbed in the evaporator, the suction pressure decreases from its normal
pressure. This drastically reduces the efficiency of the system.

Condenser Fan and Associated Cicuit Failure

A fault occurring in the condenser fan and associaled circuit can also be indicated
by the fan blade not turning. This creates a higher head pressure since less heat is
being removed from the condenser coil. This will cause a greater pressure
differential, resulting in a warm cooling area.

Compressor Motor and Associated Circuit Failure

A fault occurring in the compressor motor can appear in the following ways: the
compressor will not run, which will result in no cooling and equal pressures on bolh
sides of the system. The fault may be the result of an open winding on the
compressor motor.

Before replacing the compressor, you should first check for external troubles,
including the power connections, lhe internal thermostat, the wire terminals, the
compressor relay, and lhe compressor capacitor (if any).

Once these components have been found operational, the compressor motor is
probably at fault.

Pressure Controller and Associated Circuit Failure

A typical fault in a high- or low-pressure controller can be a broken or loose

connection. This type offault can be indicated in several ways. The compressorwill
not run, and the system will therefore not operate.

Troubleshooting Electrical Control Circuits

Troubleshooting the electrical control section of a refrigeration system requires that

a systematic troubleshooting procedure be used, in orderto Iimit the numberoftests
to be performed.

The best way to start is to observe the symptoms in order to relate the problem to a
specific section of the circuitry. The choice of which circuit section to analyze should
not be done on a random basis, as industrial control circuits can be quite complex.

The two most often used methods of troubleshooting are the voltmeter method and
the ohmmeter method.
 TROUBLESHOOTING

Voltmeter Method of Troubleshooting

The voltmeter method consists in tracing the voltage along a circuit branch or path
suspected to be defective, using a voltmeter. Basically, this method requires that the
voltage supplied to each component in the branch or path be checked to detect an
abnormal voltage level.

Figure B-1 shows this method for the electrical control circuit of the training system,
when a problem is suspected in the branch of the solenoid valve.
ELECTRONIC
PRESSURE
POWER CONTROLLER
swrrcH
(cLosED) :' CoMPRESSOH
^z 120 (230) VAC Y
----<v--o----------<: o

THERMOSTAT
SPEED SPEED
CONTROL CONTBOL

120 (230) VAC

= 120 (230) VAC_ < 120 (230) VAC < 120 (230) vAc
TP3 TP4 TP6

120
(230) vAC

,, HEAT EVAPOBATOR CONOENSER

, SOURCE VALVE FAN FAN
,
I
I
I
I
| 1l
tll
rl
L-Ol-O--l1r tt
-tttt"'
tt -
COMPHESSOR ''utttt -t--t'ttt
(22O I 24OVAC
MODELS ONLY)

VOLTMETER

Figure 8-1. The voltmeter method of troubleshooting a circuit branch.

The AC source voltage is checked first. With the POWER switch set to ON
(closed), the positive (+) terminal of the voltmeter is connected to TP1 , while the
common (COM) terminal of the voltmeter is connected to TP2 (circuit COMMON).
The voltmeter should indicate the source voltage. lf not, the source itself, the
POWER switch, or the leads connecting these components may be damaged or
open.

lf the supply voltage is correct, the + terminal of the voltmeter is moved to

measure the voltage applied to the solenoid of the valve (TP3), while the COM
terminal is left connected to the common side of the solenoid valve (TP2).
Assuming that the sensed temperature is above the thermostat setpoint, the
thermostat switch should be closed, so that the voltmeter should indicate the

REF RIG ERATI O N TRAI N I NG SYSTEM

TROUBLESHOOTING

source voltage approximately. lf not, the thermostat, the solenoid valve, or the
leads connecting these components (between TP1 and TP2 ) may be damaged
or open (infinite resistance).

It is important to understand, here, that voltage tracing along a branch or conducting

path requires that allthe components in that path be in the closed condition to permit
the flow of current through the path.

The same method could be used, for example, to test the branch ofthe evaporator
fan. ln that case, a voltage divider is created at the SPEED CONTROL knob.
Consequently, if there is no fault in this branch, the voltage between TP4 and TP2
will be less than the source vollage, and will be 0 V if the knob switch is set to OFF.

Ohmmeter Method of Troubleshooting

The ohmmeter method, also called continuity test method, consists in testing the
completeness of a path for the purpose of detecting a broken conneclion leading to
a component or a fault in the component. lt requires that the resistance of each
componenl and lead in the path be measured with an ohmmeter to detect an open,
or infinite-resistance condition.

When the path to test has two or more branches in parallel, the ohmmeter method
requires that each branch be tested separately by disconnecting the branches from
each other.

Figure 8-2, for example, shows ohmmeter lesting of the heat source of the training
system. The test leads ofthe ohmmeter are connected across the heat source. Since
the branch of the heat source has other branches in parallel, this branch must be
opened otherwise the measured resistance will correspond to the equivalent
resistance of all the other branches, not that of the heat source only. This condition
can easily be fulfilled just by opening the HEAT LOAD switch.

To lest the solenoid valve, the same principle applies: the thermostat NO contact
must be open, that is, lhe temperature in the cooling chamber must be lowerthan the
thermostat setpoint, in order for the branch of the valve to be isolated from lhe
others. Otherwise, you will have to open the branch leading to the valve (at TP3), as
the figure shows.

The same principle applies to test the continuity of the evaporator fan, compressor,
or condenser fan.
 TROUBLESHOOTING

ELECTRONIC
PRESSURE
POWER CONTROLLER
SWITCH
COMPBESSOR
(oPEN)

THERMOSTAT

120
(230) VAC

HEAT EVAPOFATOR

,
, SOURCE FAN

I
! tP2
I

I or=*
LEGEND: 1z- BRANCH
cncur
I

OHMMETER

Figure 8-2. The ohmmeter method of testing the continuity of a branch or component.

RE F RI G ERATI O N TRAI N I NG SYSTE'U

 Job Sheet
TROUBLESHOOTING

OBJECTIVE

ln this job, you will set up the Refrigeration Training System fortypical operation, and
then ask your instructor to insert a fault in the electrical control circuit. You will be
guided through step-by-step observations and questions to approach the problem
and locate the fault in a logical and systematic way. You will locate another fault by
yourself.

EQUIPMENT REQUIRED

Lab-Volt Refrigeration Training System, Model 3431

PROGEDURE

Setting Up the System

! 1. On the control panel of the Refrigeration Training System, make sure the
main POWER switch is set to OFF (O).

Connect the Refrigeration Training System to the computer used to run the
LVHVAC software, via a USB cable. Turn on the computer and then run the
LVHVAC software.

tr 2. On the Refrigeration Training System, make the following settings:

COMPRESSORswitch ..... OFF(O)

EVAPORATOR-FANSPEEDcontrolknob. ... HIGH
CONDENSER-FAN SPEED control knob . Half of HIGH
HEATLOADswitch .... ON(l)
Thermostatsetpoint .....5'C(41'F)
Manually-operated valves
V1 . . . .. . Open (handleturnedfullycounterclockwise)
V2 . . . Closed (handle turned fully clockwise)
V3 . . . Closed (handle turned fully clockwise)

tr 3. Turn on the Refrigeration Training System, then turn on the compressor.

tr 4. Wait for about 20 minutes in order for the system to stabilize and a
compressor cycle to be completed.

RE F RI G ERATI O N TRAI N I NG SYSIEM

TROUBLESHOOTING

n 5. Perform the visual checks below to become very familiar with the operation
of the system under the current conditions:

Note: Io help you in doing the inspection, it is recommended that

you peiorm voltage measurements in the electrical control circuit
at the bottom of the trainer front panel, and monitor the system
signals and parameters in the LVHVAC software. Figure 8-3
shows typical signals on the Trend Recorder under the current
syslern conditions.

a. While the compressor is running, observe the pressures indicated by

the LP and HP gauges. These pressures should be around the normal
compressor pressures with the heat load applied, as recorded in
Tables 1-4 andT-4.

b. The pressure controller reading corresponds to the pressure indicated

on the LP gauge. The compressor stops when the LP-side pressure
reaches the controller cut-out setting of 0.69 barg (1 0 psig), and restarts
when this pressure has risen to the controller culin setting of 2.1 barg
(30 psis).

When the temperature in the cooling chamber gets close to the setpoint,
the valve solenoid is de-energized (a weak click can be heard). Shortly
after that, the valve solenoid is re-energized (a loud click can be heard).

d. While the compressor is running, the condenser fan is also rotating. A

stream of air can be felt when placing a hand on the condenser coil fins.

e. The evaporator fan is rotating.

f. ln the cooling chamber, the light bulbs are both lit.

 TROUBLESHOOTING

E Trend Recordel
Flc Vi6v,, A€+IJiHon Hch

> lr t E€
sctthgs +x
lE= o-l
Ia- E-l
E
18 Cuftent Time (nrin) 53,42
fursor State m*-*-l
Eursor Position (nrin)

L6
Scale{nrin) |al
E
Des.ription talue
Pressure I 6,7ts
1.1
I Pressure
Prersura 3
2 1,55

t2
IIF Temperature
Temptrature 2
I "

TEXIPERATURE 7 Temperature 3
(cooLrNG GHATBER) Temperature 4
Temperature 5
l0 Temper6ture 6
Temperature 7 18.59
Current

8
Voltale 0
EfFecti'/e Porr'lar

-28

-3t1

! ;

Figure 8-3. Typical signals as seen on the Trend Recorder under the current system conditions.

tr 6. Once the Refrigeration Training System has been checked for proper
operation, turn it off by setting the POWER switch to O (OFF). Do not modify
the system settings.

Ask your instructor to insert the fault intended for the guided troubleshooting
of the Refrigeration Training System, as indicated in the /nstructor's Guide
for the Refrigeration Training Sysfem job sheets.

n 7. Turn on the Refrigeration Training System by setting the POWER switch to

oN (l).

REF RI G ERATI O N T RAI N I NG S YSIEM

TROUBLESHOOTING

n 8. First perform visual checks to see if abnormalities can already be pointed

out.

Observe the LP- and HP-gauge readings over a cerlain lapse of time. Do
they remain stable around the values previously noled under normal
operation? Relate your observalions to the operation of lhe compressor.
Record your observations below.

i9. Using the LVHVAC software, observe that the temperature in the cooling
chamber is above the thermostat setpoint of 5'C (41"F), and that it
increases over time. ls this your observation?

!Yes trNo

Also, observe thatthe pressure differentialacross the compressor becomes

increasingly lower over time, tending lowards a stable value, since the
compressor remains off most of the time. ls this your observation?

!Yes nNo

tr 10. ls the evaporator fan rotating?

DYes lNo

! 11. Since the compressor slarts and stops when the LP-side pressure reaches
the cutin and cut-out setpoints of the low-pressure controller, respectively,
do the compressor and controller seem to operate properly?

[]Yes !No
Does the refrigerant flow to the evaporator seem to be blocked at some
point ofthe system, preventing the system from giving up sufficient thermal
energy to keep the temperature in the cooling chamber around the
thermostat setpoint?

! Yes trNo
 TROUBLESHOOTING

! 12. Since the temperature in the cooling chamber is above the thermostat
setpoint, the NO contact ofthe thermostat should be closed and, therefore,
the solenoid of the valve should be energized to let the refrigerant flow to
the evaporator.

To verify this, determine whether a low-pitch sound (hum) is produced by

the solenoid. Also, touch the screw of the solenoid valve casing with the
metallic blade of a screwdriver to see if the blade is attracted to the screw.
Does the solenoid seem to be energized? Explain.

Conflrm your observation by measuring the AC voltage across the valve

solenoid. To do so, connect the voltmeter across TP3 and TP2 of the
electrical control circuit. ls the voltmeter reading around the 120
(2201240\-V AC source voltage?

CAUTION!

The test leads of the voltmeter you are using should have a
protective covering over their ends to avoid the risk of short
circuits and electric shocks. lf not, mak€ sure to connect the
test leads of the voltmeter to the positive (+) and
common (COM) terminals of the volimeterfirst, then connect
the otherends ofthe leads toihe indicated test points. Never
touch the metal parts of leads that are uncover€d while or
after connecting the test leads.

!Yes !No

tr 13. From your observations,

a. the valve solenoid might be in the open condition (infinite resistance).

b. the NO contact of the thermostat switch mighl be in the open condition
(infinite resistance).
c. the electrical leads connecting the valve solenoid to the thermostat and
to TP2 might be in the open condition (infinite resistance).
d. All of the above.

fl 14. Turn off the trainer by setting the POWER switch to OFF (O).

tr 15. Set the HEAT LOAD switch and the COMPRESSOR switch to OFF (O).
Also, setthe EVAPORATOR-FAN SPEED control knob to the OFF position.
This will open all the electrical branches in parallel with that of the solenoid
valve and, therefore, will allow you to perform resistance measuremenl in
that branch.
TROUBLESHOOTING

! 16. Connect an ohmmeter to TP3 and TP2 of the electrical control circuit in
order lo measure the resistance of the valve solenoid. ls this resislance
quite low (about 200 Q at 120 VAC, or 780 Q a|2201240 VAC), indicating
that the solenoid is in good condition?

z 17. Connect an ohmmetertoTPl andTP3of the electrical control circuit. lsthe

resistance between these points approximately equal to 0 O, indicating that
the thermostat NO contact is closed and that the thermostat operates
properly? Explain.

! 18. Using the ohmmeler, check if the NO contact of the thermostat is

operational: remove lhe thermostat cover, and verify that the resistance
between the uppermost and lowermosl screw terminals of the thermostat
(NO contact terminals) is null (0 O), indicating proper operation of the
thermostat. ls this your observation?

! 19. Reinstall the thermoslat cover back into place and tighten the screw.

n 20. From your observations, what is the probable cause of the problem?
Explain.

! 21 . Ask your inslruclor to remove the fault inserted into the system.

! 22. Disconnect the ohmmeter from the training system.

! 23. On the Refrigeration Training System, make the following settings in order
to place the system under the initial operating conditions:

COMPRESSOR switch . . . .. OFF(O)

EVAPORATOR-FAN SPEED control knob ... . .. . . HIGH
CONDENSER-FAN SPEED control knob . . . . Half of HIGH
HEAT LOAD switch .. .......ON(l)
Thermostat setpoint ..... 5"C (41'F)
Manually-operated valves
Vl ..... . Open (handle turned fully counterclockwise)
V2 ..... . . . . . . Closed (handle turned fully clockwise)
V3..... . . . . . . Closed (handle turned fully clockwise)
 TROUBLESHOOTING

tr 24. Turn on the Refrigeration Training system, then turn on the compressor.

n 25. Wait for about 20 minutes in order for the system to stabilize and verify that
the system operates normally, that is, as it did prior to the insertion of the
fault. Then, ask your instructor to insert another fault in your system.

tr 26. Troubleshoot the system in order to locate the problem. Ask your instructor
to verify that you have correctly identified the problem and remove the
inserted fault.

! 27. When you have finished, set the COMPRESSOR switch and HEAT LOAD
switch to the OFF (O) position.

! 28. Close the LVHVAC software.

Name: Date:

I nstructor's approval :

.l
a
 Appendix ff
TechnicalData on the Refrigeration Training System

COMPONENT TECHNICAL OATA

120 VAC 220t240 V AC

Compressor Hermetic-type, 124 W Hermetic-type, 186 W

(0.167 hp), start (0.250 hp), start
capacitor, thermally capacitor, thermally
protected, 115 VAC, protected,
60 Hz, 18-A locked- 200i240 VAC, 50 Hz,
rotor cunent (LRA), 12.3-A locked-rotor
2.9-A rated load current (LRA), 2.3-A
current (RLA) rated load current (RLA)

Refrigerant R-134a R-134a

Nominal charge 1.09 ks (2.4 lb) 1.09 ks (2.4 lb)

oil Polyol esther Polyol esther

Evaporator Forced-air coil with Forced-air coil with

variable-speed fan, variable-speed fan,
enclosed in a cooling enclosed in a cooling
chamber, 120 VAC, chamber, 240 VAC,
60 Hz, 0.58 A 50/60 Hz, 0.35 A

Condenser Forced-air coilwith Forced-air coil with

variable-speed fan, variable-speed fan,
120 VAC, 60 HZ, 230 VAC, 50i60 Hz,
0.41 A 0.2 A

Thermostat setpoint (typical) 5"C (41'F) 5'C (41"F)

Pressure controller Cut-in 2.07 barg (30 psig) (1)
2.07 barg (30 psig) (1)

settings (typical) pressure

(cl1)

Delay (ASd) Null Null

(1)
Cut-out 0.69 barg (10 psig) 1r)
0.69 barg (10 psig)
pressure (CO'l )

Operating Lower point 1.4 barg (20 psig) 1r)

1.4 barg (20 psig)
(1r

pressures (typical)
(1r
Highest point 7.6 barg (1'10 psig) 7.6 barg ('110 psig) 11)

ri) 1 bargauge (barg)= 100 kPa gauge = 14.5 psagauge (psig)

Table A-'1. Technical data on the Refrigeration Training System.

 Appendix S
Unit Conversion Table

Use the following conversion factors to convert S.l. or metric measurements lo

imperial measurements and vice versa.

s.t. oR s.l. oR
FACTOR IMPERIAL UNIT FACTOR
METRIC UNIT METRIC UNIT

Length

Centimeters (cm) x 0.394 = lnches (in) x 2.54 = Centimeters (cm)

[.4eters (m) x 3.281 = Feet (ft) x 0.305 = Meters (m)

Area

Square centimeters (cm'?) x 0.155 = Square inches (in') x 6.452 = Square centimeters (cm'z)

Square meters (m'?) x 10.76 = Square feet (ft') x 0.093 = Square meters (m'?)

Volume (capacity)

Cubic meters (m3) x 35.3'1 = Cubic feet (ft3) x 0.028 = Cubic meters (m3)

Cubic meters (m3) x 264 = Gallons US (gal US) x 0.0038 = Cubic meters (m3)

Liters (l) x 0.264 = Gallons US (qal US) x 3.785 = Liters (l)

Mass

Kilograms (kg) x 2.205 = Pounds (lb or lbm) x 0.454 = Kilograms (kg)

Force

NeMons (N) x 0.225 = Pounds-force (lb; lbf) x 4.448 = NeMons (N)

Temperature

Degrees Celsius ('C) x 1.8 + 32 = Degrees Fahrenheit ("F) 32 x 0.55 = Degrees Celsius ('C)
Kelvins (K) x 1.8 = Degrees Rankine ('R) x 0.556 = Kelvins (K)
 s.t. oR s.t. oR
FACTOR IMPERIAL UNIT FACTOR
METRIC UNIT METRIC UNIT

Thermal energy

Joules (J) x 0.00095 = British thermal units x 1054 = Joules (J)

(Btu)

Power

Watts (W) x 0.00095 = British thermal units per x 1054 = Watts (W)
second (Btu/s)

Pressure

Kilopascals (kPa) x 0.145 = Pounds-force per x 6.895 = Kilopascals (kPa)

square inch (psi; lbflin'?)

Kilopascals (kPa) x 4.018 = lnches of water @ 60'F x 0.249 = Kilopascals (kPa)

(inHrO)

x '14.5
Bars (bar) = Pounds-force per x 0.069 = Bars (ba4
square inch (psi; lbflin'?)

l\.4illimeters of mercury x 0.536 = lnches of water x 1 .866 = l\.4illimeters of mercury

@ 0'C (mmHg) @ 60'F (inH,O) @ 0'C (mmHs)

Volumetric flow rate

Cubic meters per x 35.3'14 = Cubic feel per x 0.0283 = Cubic meters per
second (m3/min) minute (ft3/min) second (m3is)

Cubic meters per x 35.314 = Cubic meters per second x 0.0283 = Cubic meters per
sec (m'/s) (ft3/s) sec (m3/s)

Table B-1. Conversion factors

 Appendi" C

Temperafure Scales
Figure C-1 shows a comparison of the four temperature scales in use today. Each
scale is named after the scientist who created it.

WATEB
BOILING 1OO
POINT

ICE MELTING
POINT
__1f.1.!

R-134a -26.1 444.8

BOILING
POINT AT
ATMOSPHERIC
PRESSURE

THEBMODYNAMIC
ZERO _27O.15

CELSIUS KELVIN FAHRENHEIT RANKINE

SCALE CC) SCALE (K) SCALE (F) SCALE CR)

Figure G-l. Comparison of the Celsius, Kelvin, Fahrenheit, and Rankine scales.
 Appendix p
Enthalpy Table for R-134a Refrigerant

TEMPERATURE,
ENTHALPY
PRESSURE at I
t
LIOUID VAPOR

-20.0'c (4.0'F) 1.3 bar abs. (19.3 psia) '173.6 kJ/kg (10.9 Btu/lbm) 386.6 kJ/kg (102.5 Btu/lbm)

-18.0'C (-0.4"F) 1.5 bar abs. (21.0 psia) 176.2 kJ/kg (12.0. Btu/lbm) 387.8 kJ/kg (103.0 Btu/lbm)

-16.0'C (3.2'F) 1.6 bar abs. (22.8 psia) 178.8 kJ/kg (13.1 Btu/lbm) 389.0 kJ/kg (103.6 Btu/lbm)

-14.0'C (6.8'F) 1.7 bar abs. (24.8 psia) '181.4 kJ/kg ('14.3 Btu/lbm) 390.2 kJ/ks (104.2 Btu/lbm)

-12.0'C (10.4'F) 1.9 bar abs. (26.8 psia) 184.1 kJ/kg (15.3 Btu/lbm) 391.5 kJ/kg (104.6 Btui lbm)

-10.0"c (14.0'F) 2.1 bar abs. (30.0 psia) 186.7 kJ/kg (16.5 Btu/lbm) 392.7 kJ/ks (105.2 Btu/lbm)

-8.0'c (17.6'F) 2.2 bar abs. (31.5 psia) 189.3 kJ/kg (17.6 Btu/lbm) 393.9 kJ/kg ('105.7 Btu/lbm)

-6.0'c (21.2'F) 2.3 bar abs. (33.9 psia) 192.0 kJ/kq (18.7 Btu/lbm) 395.1 kJ/kg (106.2 Btu/lbm)

-4.0"c (24.8"F) 2.6 bar abs. (37.3 psia) 194.7 kJ/kg (20.0 Btu/lbm) 396.3 kJ/kg (106.7 Btu/lbm)

-2.0"C (28.4"F1 2.7 bar abs. (39.4 psia) 197.3 kJ/kg (21.1 Btu/lbm) 397.4 kJ/kg (107.2 Btu/lbm)

0.0'c (32.0'F) 2.9 bar abs. (42.5 psia) 200.0 kJ/kg (22.2 8tu/lbm) 398.6 kJ/ks ('107.7 Btu/lbm)

2.0'c (35.6'F) 3.2 bar abs. (45.7 psia) 202.7 kllks (23.4 Btullbn) 399.8 kJ/kg (108 2 Btu/lbm)

4.0'c (39.2'F) 3.4 bar abs. (49.0 psia) 205.4 kJ/kg (24.7 Btu/lbm) 400.9 kJ/kg (108.7 Btu/lbm)

6.0'c (42.8"F) 3.6 bar abs. (52.5 psia) 208.1 kJ/ks (25.7 Btu/lbm) 402.1 kJ/ks (109.2 Btu/lbm)

8.0"c (46.4'F) 3.9 bar abs. (56.3 psia) 210.8 kJ/ks (26.9 Btu/lbm) 403.2 kJ/ks (109.7 Btu/lbm)
10.0'c (50.0"F) 4.2 bar abs. (60.2 psia) 213.6 kJ/ks (28.0 Btu/lbm) 404.3 kJ/kg (110.2 Blu/lbm)

12.0'C (53.6'F) 4.4 bar abs. (64.3 psia) 216.3 kJ/kg (29.2 Btu/lbm) 405.4 kJ/kg (110.7 Btu/lbm)

14.O'C (57.2'F\ 4.7 bar abs. (68.6 psia) 219.1 kJ/kg (30.5 Btu/lbm) 406.5 kJ/kg (111.1 Btu/lbm)

16.0'C (60.8"F) 5.0 bar abs. (73.1 psia) 221.9 kJ/kg (31.7 Btu/lbm) 407.6 kJ/kg (111.6 Btu/lbm)

18.0'C (64.4"F) 5.4 bar abs. (77.9 psia) 224.7 kJ/kg (32.8 Btu/lbm) 408.7 kJ/kg (112.1 Btu/lbm)

20.0'c (68.0'F) 5.7 bar abs. (82.9 psia) 227.5 kJ/kg (34.0 8tu/lbm) 409.8 kJ/kg (112.5 Btu/lbm)

22.l',C (71.6"F\ 6.'l bar abs. (88.2 psia) 230.3 kJ/kg (35.3 Btu/lbm) 4'10.8 kJ/kg (113.0 Btu/lbm)

24.O'C (75.2'Fl 6.5 bar abs. (93.7 psia) 233.1 kJ/kg (36.5 Btu/lbm) 4'11.8 kJ/kg ('113.4 Btu/lbm)

26.0'C (78.8'F) 6.9 bar abs. (99.4 psia) 236.0 kJ/kg (37.8 Btu/lbm) 412.8 kJikg (1'13.9 Btu/lbm)

28.0"C (82.4',F) 7.3 bar abs. (105.4 psia) 238.8 kJ/ks (39.0 Btu/lbm) 413.8 kJ/kg (114.4 Btu/lbm)
30.0'c (86.0'F) 7.7 bar abs. (1'l1.7 psia) 241.7 kJ/kg (40.2 Btu/lbm) 414.8 kJ/kg (114.7 Btu/lbm)

32.0'C (89.6'F) 8.2 bar abs. (118.2 psia) 244.6 kJ/kg (41.6 Btu/lbm) 415.8 kJ/kg (115.2 Btu/lbm)

34.0'C (93.2'F) 8.6 bar abs. (125.2 psia) 247.5 kJi kg (42.7 Btu/lbm) 416.7 kJ/kg (115.5 Btu/lbm)
 Enthalpy Table for the R-134a

ENTHALPY
TEMPERATURE,
PRESSURE at t
t LIQUID VAPOR

36.0'C (96.8'F) 9.2 bar abs. (132.3 psia) 250.5 kJ/kg (44.1 Btu/lbm) 417.7 kJlkg (116.0 Btu/lbm)

38.0"C (100.4'F) 9.6 bar abs. (139.7 psia) 253.4 kJ/kg (45.3 Btu/lbm) 418.6 kJ/kg (1 16.4 Btu/lbm)

40.0"c (104.0'F) 10.2bar abs. (147.5 psia) 256.4 kJlkg (46.6 Btu/lbm) 419 4 kJlkg (1 1 6.7 Btu/lbm)

42.0'C (107.6'F) 10.7 bar abs. (155.5 psia) 259.4 kJ/kg (47.8 Btu/lbm) 420.3 kJ/kg (1 17.2 Btu/lbm)

44.0"C (1 11.2"F) 1 1 .3 bar abs. (163.9 psia) 262.4 kJ lkg (49.2 Btu/lbm) 421 .1 kJlkg (117.5 Btu/lbm)

46.0'C (114.8'F) 1 1.9 bar abs. ('172.6 psia) 265.5 kJ/kg (50.5 Btu/lbm) 421 .9 kJlkg (117.9 Btu/lbm)

48.0"C (118.4"F) 12.5bar abs. (181.3 psia) 268.5 kJ/kg (51.8 Btu/lbm) 422.7 kJlkg (118.1 Btu/lbm)

s0.0"c (122.0'F) 13.2bar abs. ('191.4 psia) 271.6 kJlkg (53.1 Btu/lbm) 423.4 kJlkg (1 1 8.5 Btu/lbm)

52.0"C (125.6'F) 13.9 bar abs. (201 .6 psia) 274.7 kJlkg (54.5 Btu/lbm) 424.2 kJlkg (1 1 B.B Btu/lbm)

54.0"C (12s.2"F) 14.6 bar abs. (211.7 psia) 277.9 kJlkg (55.9 Btu/lbm) 424.8 kJlkg (1 1 9. 1 Btu/lbm)

56.0'C (132.8'F) 15.3 bar abs. (221.9 psia) 281.1 kJ/kg (57.3 Btu/lbm) 425.5 kJlkg (1 19.4 Btu/lbm)

Table D-1 . Enthalpy of saturated liquid and vapor for the R-134a.

TRAINING SYSTEM
|ob-
 Appendix [,
Pressure/Enthalpy Diagram for R-134a Refrigerant

AESOLUTE ABSOLUTE
PRESSURE PRESSURE
(1rlPa, abE.) (bar, abr.)

I ths
10
I)ul\rttt l lurrnrltcnt icirls
HFC-134a
:V"'Stt"sYlS, 100
8
6
Pressue-Enthalpy Diagram
{Sl Units)
\,Y 60
CRITICAL
PRESSURE
AREA
i-,',2
rx L,
1 i..\ r' , 40

I
2 o
I
I
1
e.
Jl
0.8 E
o 8
o
0.6 F. 6
9.
---L
0.4 :DI 4

i
0.1
^o
0.08
?a :(.r SATURATED
)+ r.{' VAPOR
UNE
0.06

0.04
,
.50
I4r
002
tJ
tul

0.01 EI{THALPY
(kJ /ks)

Figure E-1. Pressure/enthalpy diagram for R-134a refrigerant (S.1. units).

 Pressure/Enthalpy Diagram for R-134a Refrigerant

ABSOLUTE
PRESSURE

I
I)ul\nrt l lu()Iocllcrricxl\ or CRMCAL

HFC-134a o. o. .o \ir,/
'A ,Z
PRESSURE
AREA
Pressure-Enthalpy Dngranl
(English Units)
I I\
rl
il ru SATURAIED
100 LIQUID
LII{E
80
60

40 SATURATED
VAPOR
LINE

t-l I
-.Li;
10 L-; I j',I rc' ,o
8
o'l<) I.. /?
.:Lit'-oo
/

6 ilffit',[i
4 li#flt+ PeSi
lJ,{[f +x
=o -
(\lc) n (r(O|\.. O ol O - tu c) l' t.) (o
YOOOOOOOOOOF
oooa
ir.i
' o'l

ffi
9 dci <ido o ci odo6o o oo6o
+A141-L1i+|'-inH
itiiilltit!l l ENTHALPY
(Btu , lbm)
100 120

Figure E-2. Pressure/enthalpy diagram for R-l34a rerrigerant (lmperial units).

 Appendix p
Reference Textbooks

Modern Refrigeration and Air Condition,ng, Althouse, Turnquist and Bracciano, The
Goodheart-Willcox Company lnc., 1996, ISBN 1-56637-300-X

LVHVAC Heating, Ventilating, and Air Conditioning, Level One, The National Center
for Construction Education and Research, Pearson Education lnc., Prentice Hall,
2001 , rsBN 0-13-060480-1

Refigeration and Air Conditioning, An lntroduction to HVAC/R, Larry Jeffus, Air

Conditioning and Refrigeration lnstitute, Pearson Prentice Hall, 2004,
rsBN 0-13-09257'l -3
 Appendix Q
Post-Test

1. Which of thefollowing devices convertslhe low-temperature, low-pressure liquid

refrigerant into a low-pressure, low-temperature vapor?

a. The compressor
b. The expansion (metering) device
c. The condenser
d. The evaporalor

Superheat can be defined as the thermal energy

a. added to the refrigerant after it has completely turned into a vapor.

b. required to turn a liquid refrigerant into a gas.
c. absorbed by the refrigerant while it is changing state.
d. removed from liquid refrigerant after it has reached its condensing point.

3. Sensible heat is

a. thermal energy gained or lost during a change of state.

b. the gained or lost energy that causes the temperature of the refrigerant to
change.
c. thermal energy gained or lost that does not cause a change in the
temperature of the refrigerant.
d. thermal energy transferred from the refrigerant to a hotter fluid or body.

4. The expansion (metering) device

a. makes the breakpoint between the condenser and the evaporator.

b. produces a restriction through which the refrigerant is forced to flow.
c. causes the pressure of the liquid refrigerant to drop, and the boiling point of
the liquid to drop accordingly.
d. All of the above.

5. Gauge pressure is

a. the air pressure in outer space, that is, 0 bar (0 psi or 0 kpa).
b. the pressure measured above the atmospheric pressure, that is, without
including this pressure.
c. usually expressed in bar absolute or psia.
d. the pressure measured below atmospheric pressure.
 Post-Test (cont'd)

6. The compression ralio of a compressor

a. is a pure number indicating the efficiency of the compressor when using a

particular refrigerant.
b. is the ratio of the absolute pressure on the suction side to the absolute
pressure on the discharge side.
c. must be below a maximum recommended value, which depends on the
refrigerant used, otherwise a loss ofefficiency or damage to the compressor
may occur.
d. All of the above.

7. (Refer to Appendix E). The pressure-enthalpy diagram ofa particular refrigerant

a. has a horizontal axis graduated in absolute pressure units, and a vertical

axis graduated in enthalpy units.
b. has two lines indicating the changes in state between saturated vapor (right
hand line) and saturated liquid (left-hand line).
c. has horizontal lines of constant absolute pressure.
d. cannot be used to determine the amount of thermal energy absorbed or
removed by the refrigerant between two points.

8. The refrigeration cycle ofa system can be represented by a simplification ofthe

pressure-enthalpy diagram of the refrigerant it uses (see Fig. 4-10). ln the
refrigeration cycle,

a. the upper horizontal line corresponds to a change of state from vapor to

liquid, as the refrigerant flows lhrough the condenser: lhe temperature and
absolute pressure of lhe liquid refrigerant stay constant, but the enthalpy
decreases from right to left.
b. the left-hand line corresponds to the passage of the refrigerant through the
expansion device: the absolute pressure stays constant, while the enthalpy
drops.
c. the lower horizontal line corresponds to a change of state from liquid to
refrigerant, as the refrigerant flows through the evaporator: the temperature
and absolute pressure of the refrigerant stay constant, but the enthalpy
increases from left to right.
d. Both a. and c.

9. The coefficient of performance (COP) of a refrigeration system is the

a. enthalpy added to the vapor refrigerant, mainly by the work done by the
compressor.
b. enthalpy removed by evaporation.
c. ratio ofthe enthalpy removed by evaporation (N.E.R.)to the enthalpy added
to the vapor during the compressing phase.
d. indicates the efficiency of the refrigeration cycle: the lower the COP, the
better the efficiency of the system.
 Post-Test (cont'd)

10. The superheat of a refrigerant system

a. is the thermal energy added to the refrigerant after it has reached the boiling
point and completely turned into vapor.
b. can be determined by measuring the suction pressure at the sensing bulb
of the thermostatic expansion valve (TEV), then converting this pressure into
saturation temperature, and finally subtracting the saturation temperature
from the measured suction temperature.
c. gives an indication of the efficiency of the evaporator coil. For medium
temperature systems such as the Refrigeration Training System, [-16"C to
-1.1 'C (0'F to 30'F in the evaporator)1, the superheat should be between
2.8"C and 5.5"C (5"F and 10'F) approximately.
d. All of the above.

REF RIG ERATI O N TRAI N I NG S YSTE'U

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