UNIT -4 Servicing of vehicle air-conditioning systems

A/C Service Equipment

All automotive A/C systems eventually require service. A typical A/C system needs recharging every
three or four years as contamination in the system (water, incorrect oil, dirt, metal fragments, acids) can
cause a wide variety of problems.

Refrigerant Recovery & Recycling Equipment

The purpose of the Recovery & Recycling is to recover refrigerant from the air conditioning system, which
will condense, purify and store the liquid refrigerant in the unit cylinder ready for re-use.

All refrigerant must be recovered from the vehicle's A/C system prior to opening the system for repairs.
The refrigerant then must be recycled to meet certain purity standards.

The fact that R134a adds to the Global Warming Potential (also from a cost point), it is still mandatory
that it be recovered and recycled.

What’s Important:
- Use only approved Recovery and Recycling equipment (recovery units, cylinders and hoses).
- Change device filters when suggested by equipment manufacturer.
- A scale must be used to avoid overfilling the storage tank. Tank is full at 80% volume.
- Ensure oil collected during recovery is replaced into the A/C system with new oil.

Ariazone 601HD – Refrigerant Recovery & Recycling Unit

The Ariazone 601HD is lightweight all in one refrigerant recovery & recycling system for the on site
mobile technician or small workshop operator. This system has been designed to be very user friendly
and efficient for every user. Simply connect the Ariazone to the air conditioning system switch on and
walk away. The 601 will take care to the rest.

The unit is designed to be:

- User friendly (fully automatically operation)
- Safe (built in high pressure and liquid control
protection)
- Durable (compressor with thermal protection)
- Universal (recovers vapour or liquid)
- Simple maintenance (easy accessible filter)

Specifications:
- Recovery Rate: 0.2kg/min (liquid state)
- Dimensions: 230mm x 380mm x 220mm; 18kg
- LP&HP gauges - AI-D 68-L mm kl.1.0
- High pressure protection 24bar
- Large filter dryer - AI FD162-1/4"
- Oil separator OS-100/76
- Easy start compressor against high block-pressure
- Chassis - Sturdy all steel construction powder coated.
- Supply voltage - 230V/50(60)Hz
 Evacuation Equipment

A single drop of water may look harmless, but to a refrigerant system, it is the number one enemy of the
service technicians because moisture enters a system easily and is hard to remove.

- Moisture forms ice crystals at the expansion valve which retard or stop the flow of the refrigerant,
causing loss of cooling. As the expansion valve warms, due to lack of refrigerant, the ice melts and
passes through the expansion valve. The refrigerant will then start again until the moisture returns to the
expansion valve and once more builds ice crystals. The result is intermittent cooling.
- Moisture mixed with refrigerant creates corrosion trouble.
- Some refrigerant oil attracts moisture and will absorb it rapidly if left open to the atmosphere. Water-
formed acid mixes with refrigerant oil, forming a closely bonded mixture of fine globules. The effect is
called "sludging" and greatly reduces the oil's lubrication ability.

The most effective way to eliminate moisture from a system is with a good vacuum pump.
The purpose of a vacuum pump is to remove moisture and air from an A/C system. Vacuum pump
actually does not "suck out" the liquid moisture, but causes it to boil in to a vapour state which can be
harmlessly removed from the system and exhausted through the vacuum pump exhaust.

Modern systems are built tighter and charges are more critical.
That means these systems have a greater sensitivity to moisture
and other contaminants, making thorough evacuation more
important than ever before.

What’s Important:
- Use 2 (dual) stages vacuum pump only.
- Use 3/8” connection hoses between the pump and m-fold.
- Minimum capacity 2.5cfm (70lit/min)
- Change the vacuum pump oil every 30-40 working hours. Use
only high quality vacuum pump oil.
- The lower number in microns, the better the pump.
- Dehumidification starts properly at levels of 1,000 microns (or
less). The use of an electronic vacuum gauge clearly indicates
Microns can be measured with special digital
whether the level is reached and whether it is maintained as well. vacuum gauge only.

Ariazone Vacuum Pump (with solenoid valve and vacuum gauge)

Dual stage vacuum pump with solenoid valve and

vacuum gauge, easy to carry due low weight. Very low
noise levels make it a pleasure to operate.
- Two stages
- Vacuum gauge D80mm with adjustable pointer
- Large solenoid valve
- 3x10Pa (25 microns) ultimate Vacuum
- 3.5 CFM (100 l/min)
- Finned alum. housing for lower operating temperature
- Motor 190 W (1/4 HP), Capacitor start,
- Intake fitting 3/8” & 1/4" SAE flare
- Oil capacity 300 ml
- Power supply - 230V / 50-60Hz
 Charging Equipment

The purpose of the refrigerant charge equipment is to batch a user-defined weight amount of refrigerant
into the air-conditioning system. Charging correct amount of refrigerant will ensure the proper capacity
and efficiency from air-conditioning system.

Important: Before start refrigerant charge A/C system MUST be properly evacuated and leak tested.

Charging by weight by using the digital refrigerant scales is the most accurate and fastest methods of
charging a system that has a known refrigerant charge (manufacturer recommendation).

What’s Important:
- Use only precise charging stations equipped with solenoid valve for automatic charge shut-off.
- 50kg minimum weight

Electronic scale with automatic charge shut-off

Specifications:

Weighing range: 50kg(110lb)

Resolution: 2g/0.01lb/0.1oz
Accuracy: 0.05%
Display: LCD (7 segment)
Power: 220V or 110V AC P
Platform Size: 237×237mm
Weight: 5kg
 All in One Unit – Automatic A/C Service Station

Rather than have a machine that only recovers refrigerant and then a vacuum pump and charging scale
to complete the task of servicing an A/C system, there are all in one machines that incorporate all the
necessary functions required to start and complete a full air conditioning system diagnosis and service,
which can operate manual (step by step) or in fully automatic mode.

Basic functions of all in one unit include:

- A/C system test by reading the gauges
- Refrigerant Recovery & Recycling
- Recovered Oil Drain
- Evacuation of the system
- Oil & UV Dye Injection
- Refrigerant Charge by weight

Above basic, Full Automatic machines features:

- Automatic Oil Reintegration
- Vehicle Database
- Integrated Thermal Printer
- Refrigerant Management
- USB connection to PC

Last generation advanced machines also features:

- Flushing the A/C system with refrigerant
- Oil injection for electric compressors
- Diagnostic of a/c system failures
- Refrigerant analyzer
- Wireless temperature probes
- Wireless Bluetooth connection with PC
- Touch Screen

What’s Important:
- The unit must be able to recover 95% of the refrigerant contained in the air con within 30 minutes.
- Refrigerant must be charged with an accuracy of +/- 15 g.
- Refrigerant recovery must be made and displayed with an accuracy of +/- 30 g.
- Dual stage vacuum pump minimum 2.5cfm (70lit/min) or larger.
- High efficiency filtration and oil separation system
- Regular maintenance of the unit (calibration, filter and vacuum pump oil change).

Ariazone 5001 FAHD Ariazone 6001

Full Automatic A/C Service station Advanced Refrigerant Processor
A/C Flushing Equipment

When a compressor fails, a lot of metallic debris is often thrown into the system. Most of this debris
collects in the condenser where it can cause blockages that reduce cooling performance. Debris can plug
the orifice tube or expansion valve. This can block the flow of refrigerant and lubricating oil causing a loss
of cooling and possible compressor damage. Flushing the system is the best way of removing residual oil
and contaminants, when performing a compressor replacement.

Flushing can help prevent repeat compressor failures and system blockages by dislodging and cleaning
out sludge and debris. Replacing badly contaminated parts such as the condenser, accumulator or
receiver-drier and orifice tube or expansion valve is another way to get rid of these contaminants, but
flushing is usually more economical choice. Regardless of which approach you use, the orifice tube or
expansion valve should always be replaced when contamination is found.

Sludge is usually the result of moisture-contamination. The blackish goo that results can damage the
compressor and plug the orifice tube or expansion valve. The moisture-absorbing "desiccant" in the
accumulator or receiver-drier is supposed to prevent this from happening. But the desiccant can only hold
so much moisture. Once saturated, sludge begins to form

Another reason for flushing is to remove residual lubricating oil from the system.

The basic concept behind any flush job is to remove the oil and contaminants from the A/C system. In
most cases, contaminants and debris will 'stick' to the oil. If you can remove all the oil, you will remove all
the contamination.

Regardless of the type of A/C system you are flushing, never attempt to flush the compressor,
accumulator or receiver drier. Orifice tube, filter drier and accumulator must be replaced.

Flushing unit works on the principle of pulsing operation during the cleaning process. The solvent is
recovered within the machine and the purified solvent returned into the cylinder. This flushing procedure
ensures effective and fast cleaning out of difficult contamination.

Using high-pressure, up to 8 bar, particles and soot are forcefully flushed out. A special pulsing operation
applies additional abrasive degreasing action to remove soot and dirt from crevices and corners. Due to
its low boiling point the solvent can easily be recovered from the equipment and leaves it dry and clean.

Eko-Flush K570
Workshop units for use in larger service and repair shops, and
automotive garages
This unit can conveniently be used for systems up to 20 L volume.

Specifications:
Connection with the flushed device 3/8” SAE (5/8” UNF)
Power supply: 230V/50Hz
Maximum power input: 1350W
Dimensions: 570x605x950mm
Weight: 54kg
 Leak Test & Detection Equipment

Leakage of refrigerant from a/c system affects the performance of a sealed system. Both suction as well
as discharge pressures reduce due to loss of refrigerant. Due to lower suction pressures, the lubricating
oil return becomes difficult. In addition to this possibility of oil leaking with refrigerant may lead to the
damage of the compressor. If the suction pressure due to refrigerant leakage falls below atmospheric
pressure, then there is a possibility of air leaking into the system. This will bring moisture into the system
and cause internal components to corrode.

There are 2 main methods for leak test the a/c system:

Leak Test under Vacuum. When a vacuum is drawn (minimum 1000 microns or lower) on the system
and the vacuum pump is then turned off, it is a good practice to allow the system to sit for about 20-30min
with the gauges connected to monitor. If vacuum is lost during this time, it indicates a leak is present.
Note that the vacuum test is not conclusive. System may have leaks under vacuum that do not appear
under normal system pressure, and vice-versa. Still, it's not a good sign.

Pressure Hold Leak Test. The most reliable method for leak testing the automotive
A/C system is using nitrogen. For a complete A/C system test, the system should be
pressurized to 15bar (200 psi) with nitrogen. Allow the system to sit for at least 20-30
minutes. If there is no degradation in the pressures, the A/C system is free of leaks.
Nitrogen MUST be used with care and caution, because it is packaged under extreme
pressures as a bottled gas. Nitrogen regulator is required in order to regulate and
control the pressures of nitrogen that you put into the A/C system. For best results, it
is suggested that the nitrogen be connected to the A/C system through a set of
manifold pressure gauges.

Nitrogen can also be used for purging excess moisture from A/C systems and for
flushing. Nitrogen is known to be a very dry and inert gas. What’s best is that nitrogen
will not cause any other problems with components nor will it react with any oils or
other contaminants that may be found in the A/C system.
Nitrogen Pressure Test Kit

Both tests (under vacuum or pressure hold) will not show exactly where the leak is located. This type of
check is only useful to verify whether the system has a leak or not.

Leak Detection MethodsVisual

Leak Detection
When a refrigerant leak occurs, it is
common in some cases for the lubricant
oil to escape with the refrigerant. The
presence of oil and encrusted dust
around hose fittings, joints and
components will indicate a leakage
point.

A mixture of dishwashing liquid and

water applied around the pressurised
A/C system pipes and fittings will form
bubbles at the leakage points.
Electronic Leak Detector
These leak detectors operate in various ways. The
most common being that when the unit is turned on, a
low ticking sound can be heard and once the probe
locates a leak, the ticking sound increases to a high
pitched noise. This can be achieved by moving the
sensing tip slowly around the underside of
components and fittings at a distance of approximately
5-10 mm.

Important: DO NOT
allow the sensing tip to
contact components or
fittings as false
readings and tip
damage will occur.

Ultraviolet Fluorescent System

A fluorescent coloured dye is injected into the A/C
system and allowed to circulate with refrigerant. Then
a specially designed ultraviolet lamp is passed over
each component in the A/C system. If a leak is
evident, the coloured dye glows yellow bright. This
method is exceptionally good for pin pointing a small
leak.
It is advisable to ask the customer to return in
approximately one week time as the dye could tale
longer to emerge if the A/C system has a small leak.

Refrigerant Identifier

The best defence against unknown refrigerant, and

the risks associated with unknown refrigerant, is a
refrigerant identifier. Use a refrigerant identifier any
time a refrigerant mixture is suspected.
The main function of the refrigerant identifier is to
assist the servicing technicians to check the purity of
refrigerants in storage cylinders or directly in vehicle
air conditioning systems. These devices typically
detect R12, R134a, R22, air, and hydrocarbons.
It also determines and controls the purging of ambient
air-based Non Condensable gases (NCG) from
refrigerant storage vessels or vehicle air conditioning
systems.
Other Measuring Instruments

Mini R134a Identifier

Economy identifier for verifying the quality of R-134a refrigerants in
automotive a/c systems. It checks and verifies with a “GO” or “NO GO”
signal.

Digital Thermometer with probe

Digital IR Thermometer
This can be used for measuring the temperature of registers and grills as well
as ambient temperatures

Electronic vacuum gauge

The instrument reads from vacuum levels of 12,000 micron to … “0”, and
may be used in ambient temperatures from 0ºC to 50ºC.

Variable Displacement Compressor Tester

It controls the clutch-less variable compressors. By controlling the
displacement (independent from the onboard computer) a more precise
diagnosis can be made on the system.

Pressure Switches Tester

Tester for checking gas pressure switches. Includes adapters for the most
common gas pressure switch thread sizes.

Digital refrigerant pressure/temperature chart

This instrument offers fast and accurate temperature references on a large
and LCD display.

Sound Level Meter

To quantify sound level.

Electronic Scale
For weighing refrigerant cylinders

Nitrogen / Hydrogen Tracer Gas Leak Detector

It utilizes a solid-state heated sensor designed to be highly sensitive to
Nitrogen/Hydrogen tracer Gas. The tracer gas mixture complies with Article
6, Paragraph 3 of EU Directive 2006/40/EC.
Universal Automotive A/C Tools

Universal Orifice tube remover kit

This set of tools makes it a snap to remove orifice tubes found in automotive
air conditioning systems. Select the correct jaw, attach it to the handle and
remove the tube by simply locking it onto the tool and pulling it out.

Fin Straightener
For alignment of condenser or evaporator fins.

Valve core remover

Valve core remover for standard & JRA valves.

Hose cutter
For cutting all common sizes of A/C hoses.

Sight glass a/c diagnose

Convenient instrument to make the refrigerant flow visible. This gives an
indication about: Presence of leak “stop” substances, Compressor damage
caused by metal particles and shavings, Quality of the refrigerant oil…

Compressor seal service set

Special tools are required when replacing seals on the compressor.

Clutch tool kit

Universal tool kit for assembly & disassembly of clutches on most used
compressors.

Spring-lock tool kit

Spring-lock coupling disconnect tool for Ford, Hyundai, Volvo, Peugeot and
Citroen.

Hose Crimping Equipment

Covers all 4 standard hose dimensions.

Thread chaser kit

To re-align damaged threads on A/C specific fittings. Thread chaser kit with
various chaser sizes for making female and male thread like new again.

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Universal A/C Assortments

O-ring assortment
Universal HNBR O-ring kit for a/c systems.

Valve core set

7 different valve core and 1 small valve core remover.

Orifice tube assortment

Valve cap assortment

10 different valve caps.

GM seal & gasket assortment

An assortment of hose gaskets for GM com-pressors. Six different types, four
of each type.

Hose Ferrule set

Assortment of replacement crimp sockets in the standard hose sizes 6, 8, 10,
and 12.

Standard A/C Hose

Hose size 6, 8, 10, 12 per meter.

Compressor Guard Assortment

New or reconditioned compressors are regularly damaged by metal shavings
or dirt particles left in an air conditioning system. A simple screen in
the suction line of the new compressor can prevent this from happening.
Easy to install without cutting lines.

Foam Tape
Used for the protection and insulation of various air conditioning parts.

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Compressor Oil

The purpose of compressor oil is to provide lubrication for the compressor. It helps compressors to last
longer by providing enough grease that inhibits friction between the bearings, vanes, and rotor.
Manufacturer of the vehicles or compressors determines the viscosity and lubricant type. Use of the
correct lubricants is critical for proper system performance, durability, and longevity.

There are four major a/c compressor oils in the market today and these are:

- Mineral oil used in old R12 systems only.

- PAG oil (Poly-alkaline-glycol) used in original equipment passenger car and light truck HFC-
134a systems.
- POE oil (Poly-ol-ester or Ester for short) is synthetic lubricant specified by few vehicle
manufacturers.
- PAO oil (Poly-alpha-olefin) is synthetic oil. It is new in the market and slowly becoming popular.
Its trademark is "one size fits all", because its viscosity level is compatible with almost all types of
a/c system oils and additives, as well as with most compressors.

There are few viscosities or thicknesses of compressor oil: ISO 46, ISO 68, ISO 100, ISO 150. The
smaller number indicates less viscous oil.

Important: Most A/C compressors used in Hybrid or Electrical vehicles are driven by a high voltage
electric motor. Only the non-conductive lubricating oil (POE or PAO) can be used as the windings in these
electric motors are exposed to the A/C system lubricating oil. Even a small amount of PAG oil can
damage the high voltage insulation in an electric compressor.

MINERAL oil PAG oil POE oil PAO oil

(Poly-alkaline-glycol) (Poly-ol-ester or ester) (Poly-alpha-olefin)

R12 - Compatible R12 – NON Compatible R12 - Compatible R12 - Compatible

R134 - NON Compatible R134 - Compatible R134 - Compatible R134 - Compatible

Hygroscopic Hygroscopic Hygroscopic NON Hygroscopic

NON COMPATIBLE NON COMPATIBLE NON COMPATIBLE COMPATIBLE

with other lubricants with other lubricants with other lubricants with other lubricants

MISCIBILE MISCIBILE MISCIBILE LOW MISCIBILITY

May not prevent oil May not prevent oil May not prevent oil Prevents oil logging
logging logging logging

POOR FAIR FAIR SUPERIOR

High Temperature High Temperature High Temperature High Temperature
Viscosity Properties Viscosity Properties Viscosity Properties Viscosity Properties

NON AGGRESSIVE AGGRESIVE AGGRESIVE NON AGGRESSIVE

Electric Compressors Electric Compressors Electric Compressors Electric Compressors

NON Compatible NON Compatible Compatible Compatible

11
Component replacement

When replacing components, check the manufacturers

recommendations on the quantity of oil to be added to the
new components before installation. This is normally found in
the particular vehicle workshop manual.

EXAMPLES of approximate quantities:

Evaporator – 40ml
Filter drier – 20ml
Condenser – 30ml
Accumulator – 40ml
Hoses – 20 ml
Tubes – 20ml

Insufficient oil in the system will damage the compressordue to

lack of lubrication, but excess oil will collect in thecondenser and
prevent proper cooling performance.
If the compressor sounds as though it needs lubricating, it
probably does. Check the system for debris, and replace the
compressor if needed.
If cooling performance is poor despite several recent repairs,
the system may contain excess lubricant, especially if oil was
added to the system without draining and measuring all the
oil.

Compressor (new replacement)

Drain and measure the lubricating oil from removed

compressor. Likewise, remove the oil from the new
compressor, refill this new compressor with the same quantity
of oil drained from the old compressor.
On compressors without inspection plugs, add oil to
compressor through the discharge and suction ports, turn the
compressor hub several times by hand to make sure no
oil is trapped in the compressor chambers.

Use the new clean oil removed from the new compressor plus
10cc to allow for any internal oil.

12
Refrigerant Safety

As R134a has a very low boiling point, care must be taken when it is been handled. The following safety
precautions must be followed:

- Always wear eye protection.

- Wear gloves for Hand/Skin Protection. Don't allow R134a to contact bare skin as this causes frostbites.

- Do expose refrigerant containers to open flames, red hot surfaces, or temperature above of 50oC.

- Provide adequate ventilation when charging or recovering refrigerant as it is heavier than air. Avoid
breathing R134a vapour.

- Use care when hot water steam cleaning the engine. Hot water on the air conditioning pipes and tubes
could create thermal expansion of the refrigerant contained in the system.

- Do not transfer refrigerant from cylinder to cylinder using a pump without knowing when the bottle being
filled has reached 80% of its capacity, as a remaining 20% is used for thermal expansion.

- Do not transport refrigerant containers in the passenger compartment of a vehicle.

- Do not puncture or incinerate refrigerant containers.

13
 R134a – HFO 1234yf Handling and Service Differences

Starting in 2012 vehicles with air conditioning systems running on the new 1234yf refrigerant will enter the
European market. However, the great majority of vehicles on the roads will still be using the older R-134a
refrigerant – and these will continue to require servicing for the next 15 years or so.

HFO-1234yf has vapour pressure, toxicity class A, similar to R-134a, but has mild flammability

HFO1234yf is mildly flammable. Precautions used with other flammables (gasoline, oil) are applicable to
1234yf. In general, low lying areas, (such as workshop pits, shafts or cellar exits), may cause released
refrigerant to pool as it is heavier than air. Current regulations require work areas to be adequately
ventilated and extraction units switched on if available.
Service technicians should not smoke or have any open flame present while working on refrigerant
containing systems

R134a HFO 1234yf

Light blue cylinder White cylinder with red band

Both disposable and returnable Both disposable and returnable

containers available. containers available.

Refrigerants should always be stored in a cool, dry location, out of direct sun light.

To prepare for HFO1234yf service technicians will need:

- New 1234yf recovery/recycle/recharge equipment
- New refrigerant identifier to allow the workshop to monitor the type, quality and purity of a given
refrigerant.
- New leak detection equipment capable of identifying leaks of the new refrigerant in the vehicle’s air con
system.
- Assure adequate ventilation and follow flammable storage practices.
- Appropriate technician training

HFO1234yf refrigerant system components should not be replaced with ones removed from a system that
uses another type of refrigerant, or from a salvaged vehicle.

Lubricants used with HFO1234yf systems may be different than those currently used. hybrid
compressors, driven by high voltage electric motors, or equipped with hermetic mobile A/C systems, use
different oils. Necessary to check oil requirements.

14
Air Conditioning Performance Testing (General)
This procedure describes methods for testing and inspecting air conditioning systems. Before servicing or
diagnosing an A/C system there are preliminary checks that should take place.

STEP 1. Park the vehicle in a shaded area. Open the vehicle doors or windows to vent the interior.
Record the ambient temperature and relative humidity.

STEP 2. Visual checking for hose damage. STEP 3. Visual checking for damage on
Inspect all connectors for signs of leakage or oil. compressor housing. Inspect drive belts for
Look for kinks, bends, or weather cracking. correct tension and damage. Evaporator drain
hose not blocked.

STEP 4. Ensure the condenser cooling fins are STEP 5. Set the controls to:
not blocked with obstructions such as insects, Fresh air position; Maximum cooling;
leaves or grass. Condenser fan operates and Highest blower speed;
runs in correct direction.

STEP 6. Place a thermometer in the air outlet nearest the center of the dash for record of discharge air
temperature.

STEP 7. Connect both high and low pressure service hose coupling valves of service unit to the system
filling ports.

STEP 8. Set the transmission in neutral and start engine. Turn the A/C on and bring engine speed to
1500 RPM then allow pressure gauge needles to stabilize.

STEP 9. Record the pressure and temperature readings. Compare this to the performance charts. Note:
Take pressure and temperature readings when the compressor is engaged.

Ambient temperature Discharge air Low Side High Side

(oC) temperature oC Pressure (bar) Pressure (bar)
20 4-10 1.6 – 2.2 10 – 13
25 5-12 1.7 – 2.4 11 – 15
30 6-13 1.8 – 2.6 12 – 17
35 8-14 1.9 - 2.8 13 – 19

If the system performance is less than described on the performance chart, make necessary repairs,
perform the leak test.
15
 Pressure gauges

An accurate diagnosis and determination of air conditioning system function and more importantly,
malfunction, depend largely upon the ability of the technician to interpret gauge pressure reading. The
importance of a gauge set is often compared to that of a doctor's stethoscope.

An improper gauge reading will relate to a specific problem. More than one problem may be associated
with particular gauge reading, however. A system operating normally will have a low-side gauge pressure
reading that corresponds with the temperature of the liquid refrigerant as it becomes a vapor while
removing heat from the air flowing over the evaporator coil surface. The high-side gauge readings should
correspond with the temperature of the vapor as it becomes a liquid while giving up its heat to the
ambient air flowing through the condenser.

Any deviation from ambient dependant normal gauge readings, other than slight, indicates a malfunction.
This malfunction, if within the system, may be caused by a faulty control device, a restriction, or defective
component. It should be noted that improper mounting or location of components in a newly installed
system may affect system performance. The vehicle engine may also affect system performance and will
be note as abnormal gauge readings.

Pressure gauge pre check

Always inspect pressure gauges to ensure the needles rest as zero on both low and high sides on
atmospheric pressure. If the needle(s) do not rest on zero, remove the hoses, open both taps, detach the
dial face and gently turn the adjustable screw until the needle(s) rest on zero. Reconnect hoses and close
taps.

Pressure gauges readings in normal condition

Gauges show normal operation

ofA/C system.

If the pressure readings to the

ambient temperatures are different to
these, then the system is probably
defective.

Important: Pressure gauge

readings (low & high) depends on
ambient temperature.

16
 1. Low Pressure (Suction) vs. Ambient Temperature

Example:
The outside temperature is 25 oC. The suction pressure we have measured is 2 Bar (30psi).
The graph shows that the point is in the area of normal pressure.

2. High Pressure (Discharge) vs. Ambient Temperature

Example:
The outside temperature is 25 oC. The discharge pressure we have measured is 12 Bar (170psi).
The graph shows that the point is in the area of normal pressure.

17
 Faulty performance of A/C system

As we have mentioned before, correct pressure gauges reading may show particular problem or
associate to a possible problems.

Note: (F) fixed displacement compressor, (V) variable displacement compressor

Pressure readings are normal, A/C system is not cooling.

Probable Causes

- Warm air infiltrated into the evaporating unit or

passenger compartment.

- Warm water infiltrated in the heater.

- Ice on evaporator core.

An A/C system that blows cold air for awhile then

warm air is probably freezing up. This can be
Normal Normal caused by air and moisture in the system that allows
ice to form and block the orifice tube.

Low Pressure - Low, High Pressure - low

Probable Causes

- Normal situation if ambient temp. is very low.

- Too little refrigerant quantity. Check for leaks.

- Expansion valve (or orifice tube) stuck partially

closed or blocked.

- Blockage between filter and evaporator.

Low Low - Blockage in the H.P. branch between compressor

and condenser-filter hose, but before the H.P.
reading point.

Low Pressure - High, High Pressure - High

Probable Causes

- Normal situation if ambient temp. is very high.

- Excess refrigerant charge, 30% more.

- Condenser overheated. Faulty condenser fan

(slow or no rotation).

- Air present in the A/C system. More than 6% air

can cause a big drop in cooling performance.
High High
- (V) Compressor displacement regulator valve
defective.

- Blockage in the H.P. branch between compressor

and condenser filter hose, but after the H.P. reading
point.
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 Low Pressure - High, High Pressure – Low (Low Press. approximately equal to High Press)

Probable Causes

- Electric clutch of the compressor not engaged. If

the voltage to the clutch is low, or the clutch coils
have too much resistance, the clutch may not
engage to drive the compressor. Also check to
see if the clutch relay is receiving voltage when
the A/C is turned on.

- Compressor belt jumped. Probably caused by

misalignment of the pulleys.
High Low - Compressor damaged.

- (V) Compressor displacement regulator valve

defective.

Manual A/C systems.

- Faulty low pressure cut-out switch. This switch prevents the compressor from running if the refrigerant
level is low.

Automatic A/C systems.

- Problem in the control module, or bad sensor (an ambient air temperature sensor, interior air
temperature sensor, evaporator temperature sensor, or sun-load sensor).

Low Pressure - High, High Pressure – Low or Normal

Probable Causes

- Suction and drainage hoses reversed on

compressor.

- Electric clutch of the compressor not engaged.

- Expansion valve stuck open. If the compressor is

“variable displacement type”, the low pressure has
small but fast oscillations.

- (V) Compressor displacement regulator valve

High Low (or Normal) incorrectly set or defective

- Compressor damaged

Low Pressure - Low, High Pressure – High or Normal

Probable Causes

- Filter saturated with moisture

- (V) Compressor displacement regulator valve

stuck at maximum displacement.

- (F) Blockage in H.P. or L.P. branch between

filter and evaporator.

Low High (or Normal)

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