Refrigeration is the cooling process of removing heat from a compartment or area and sending

it to the atmosphere or any other cooling medium. In this article we see how to identify various
faults and the causes and actions to be taken to overcome those problems.

 Marine Refrigeration Systems

The objective of any refrigeration system is to collect heat from a low temperature area and
move it to a high temperature area. Refrigerant is a substance that acts as a cooling agent by
absorbing and giving off heat. Usually there are two types of refrigeration systems commonly
encountered: namely the vapor compression cycle refrigeration system and the vapor
absorption cycle refrigeration system. The most common system that is used on all ships is the
vapor compression cycle refrigeration system.
Onboard ship refrigeration systems are used in the carriage of some liquefied gases and bulk
chemicals, air conditioning for accommodations, to cool the bulk carbon dioxide for
firefighting systems, to preserve perishable foodstuff during storage, and to preserve stores on
ships like fish, meat, vegetables, and dairy products. It is required to maintain the temperature
of the above items within desired limits throughout the voyage, so the refrigeration system will
be running throughout the voyage … which may lead to various problems during its operation.
In this article let us see how to identify various faults in refrigeration systems, the causes for
the faults, and the actions to be taken to troubleshoot those problems in refrigeration systems.
Faults like under charging, over charging, air in the system, moisture in the system, and oil in
the system will be discussed in this article.

 Refrigeration Cycle

 Refrigeration Systems

 Undercharging of Refrigeration System

Indication:
 Compressor is running hot and performance of the compressor falls off due to high
superheat temperature at the suction side of compressor.
 Suction and discharge pressure of the compressor is low.
 Large vapor bubbles in the liquid sight glass.
 Low gauge readings in the condenser.
 Ammeter reading for the compressor motor is lower than normal.
 Rise in room temperature which is to be cooled.
 Compressor is running for extended period of time.
Causes:
 Leakage of refrigerant at the shaft seal, flange couplings, valve gland etc.
 Expansion valve may be blocked at the strainer.
 Partial blockage of refrigerant at the filter or drier or evaporator may cause undercharging.

 Action:
 Identify and rectify the leakage of refrigerant from the system.
 Clean the filter and drier.
 Charge the system with fresh refrigerant as required.

 Overcharge of Refrigeration System

Indication:
 The liquid level in the condenser is too high (high condenser gauge reading).
This will reduce the available condensing surface, with corresponding increase in
the saturation temperature and pressure.
 High pressure switch of the refrigerant compressor activates and stops the
compressor.
 The suction and the discharge pressures are high.
Causes:
 It may be due to the reason that excessive refrigerant has been charged in the
system.
 Air in the system may also cause over charging indication.
 It may also be due to the formation office on the regulator.
Action:
 Remove the refrigerant from the system. This is done by connecting a cylinder to
the liquid line charging valve, starting the compressor, and then operating the
charging valve.
 Purge the air from the system and maintain effective cooling.
 Remove ice from the regulator by using any of the defrosting methods.

 Moisture in the System

This normally comes with the ingress of air in the system. Moisture may freeze at the
expansion valve, giving some of the indication of under charging. It will contribute to the
corrosion in the system. It may cause lubrication problems and breakdown of the lubricating oil
in the refrigerant compressor.
Action:
 Renew silica gel in case of minor moisture.
 collect refrigenant and remove all air and moisture by vacuum pump if the
amount is huge.

 Air in the System

Indication:
 This may cause the refrigeration compressor to overheat, with a high discharge
pressure and normal condensing temperature.
 There are possibilities of small air bubbles in the liquid sight glass of the
condenser.
 Condensing pressure of the refrigerant in the condenser may be high.
 If there is excessive air, it may reduce the cooling capacity of the system, making
the compressor to run for the extended period of time.
 It may cause the gauge pointer of the condenser to jump indefinitely.
Causes:
 During charging, air may enter in to the system.
 If Freon-12 is used air may leaks in to the suction line because the working
pressure of the Freon-12 refrigerant is less than the atmospheric pressure.
Action:
 Air in the system can be removed by collecting the system gas in the condenser,
leaving the condenser cooling water on and venting out the air from the top of the
condenser because air will not be condensed in the condenser but remains on top
of the condenser above the liquid refrigerant.
  Connect the collecting cylinder to the purging line of the condenser, open the
valve, and collect air in the cylinder.
 After purging the air from the system don’t forget to shut the purging valve.
 Check the level of the refrigerant in the system. If required, charge the system
with fresh refrigerant.
 Restart the compressor with all safety precautions.

 Oil in the Refrigeration System

Indication:
 Temperature is not dropping in the cold rooms as normal, due to fact that oil act
as insulation in the evaporator.
 It may cause excessive frost on the suction line.
 Refrigerant compressor runs for the extended period of time.
 Lubricating oil level in the compressor will drop.
 Refrigerant level will fall if oil has caused blockage.
Causes:
 This may happen if the oil separator is not working properly.
 Oil may carry over from the compressor and may not come back to the
compressor due to blockage in the system.
 Defective piston rings or worn out liner of the compressor may cause the oil to
carry over along with the refrigerant.
 Compressor may take high capacity current during starting.
Action:
 Check the oil separator for proper functioning.
 Check the drier for proper cleaning and if its require cleaning clean it
 Evaporator coil should be drained to remove any trace of oil.
 If there is oil in the cooling coils, increase the condenser and evaporator
temperature differentials and remove excess frost on the suction pipe.
 Heat pipes with blow torch.

 Flooding of Refrigerant in the System

This is seen as liquid getting back to the suction of the refrigerant compressor. It may be due to
a faulty or incorrectly adjusted expansion valve and also due to solenoid valve leakage. It may
also result from overcharging of the refrigeration system. Flooding may lead to an iced up
evaporator.
8 Most Common Problems Found in
Ship’s Refrigeration System
One of the few machinery systems which needs to run continuously on ships is its
refrigeration plant. As a lifeline for all perishable food items and temperature sensitive cargo,
refrigeration plant is one of the most important systems on ships which requires utmost
attention of engineers at all times.

However, just like all other machinery on ships, the refrigeration system can also get into
some trouble from time-to-time. Some of these problems are common but require immediate
attention. Mentioned below are eight most frequently seen problems in the ship’s refrigeration
plant:

1. Compressor Starts But Stops immediately

When the compressor in the reefer circuit starts and suddenly stops, it can be because of the
following reasons:
Reasons Solutions

Ensure that all the suction line valves are in open condition, the

Low pressure cut out gets activated refrigeration is properly charged and the low pressure cut out is

not defective

Check for proper functioning of oil pressure cutout and replace

Defective oil pressure cut out
the defective cutout

If the defrost timer is getting activated frequently, leading to

Defrosting timer is getting activated frequently
cutout of compressor, check and repair defrost timer

This can be because of leakage of lube oil from seal or carry

The lube oil level is below required level
over of oil. Rectify the leakage and refill the oil level

Foaming of oil leading to reduced oil pressure Ensure no foaming takes place, renew the oil if required

Motor overload cutouts are activating Ensure that electrical motor trips are working properly

2. Compressor Start and Stops Frequently

If while maintaining the correct temperature of the ship’s provision room or reefer cargo, the
reefer compressor is frequently cutting-in and out, then such problem needs to be sorted out
immediately. The most normal causes for such operation are:

Reasons Solutions

Wrong Setting of Cutouts: It may be because the high pressure (HP) cutout is set too high or LP Check and
cutout is set too low change the
 setting to

advisable

limit

Change the

setting and

increase

Differential Setting Span is Small: The low pressure (LP) cut out is provided with starting and the span

stopping pressure setting. If the setting span is too small, it will lead to frequent cut-in and cut-out of between

the compressor starting and

stopping

compressor

pressures.

Replace all
Defective Valves: If the compressor discharge valve is leaky or the line solenoid valve is not closing
the
properly, this will lead to variation in sensor pressure and result in frequent cut-in and cut-out of
defective
compressor
valves

Clogged Suction Filters: Compressor is provided with a filter in the suction line. If that is clogged, it Clean the

will lead to frequent LP cut out filter

3. Compressor is Running Continuously

The function of compressor in a refrigeration system is to act as a pump to circulate the
refrigerant in the cooling circuit. It can happen that to maintain the cooling temperature in the
rooms, the compressor is running continuously. If this happens following can be the causes
for the same:

Reasons Solutions

Ensure thermostatic expansion

Refrigerant not sufficient for cooling evaporator valve is working properly and clean

the filters inside TEV

Correctly set the LP cut-out to

Thermostat low pressure cut-out not activated at low temperature/ pressure
correct setting

Check for leakage of refrigerant and

Refrigerant charge is low in the circuit
charge with required refrigerant

4. Unusual Sound from Compressor

One of the most common problems in any machinery is abnormal sound coming from some
of its parts. This may be due to trouble with mechanical components inside the compressor or
due to the reasons stated below:

Reasons Solutions

Reduce the capacity control

The capacity control setting is too high, leading to knocking sound during starting
setting

Ensure that the oil level is

The oil pressure is low
maintained and no foaming of
 oil is developed. Replenish or

refill the lube oil if required

Check the alignment and set

Incorrect alignment of compressor and motor motor and compressor in one

line

Ensure that the compressor

foundation is secured and all

Loose foundation
foundation bolts are checked

for tightness

Ensure to check the elasticity

Loosening of driving belt of the belt and renew if the

belt is slack

5. High Compressor Discharge Temperature

It may happen that all the provision rooms or cargo holds are maintained at correct
temperature, but in doing so the discharge temperature of the compressor is going above the
limit. This problem may arise due to following reasons:

Reasons Solutions

Recharge the circuit to maintain refrigerant

Excessive suction temperature due to less refrigerant in the circuit quantity in the circuit. Ensure TEV is set

properly and supplying enough to the

 evaporator, else degree of superheat will

result in increase of suction and discharge

temperatures of the compressor

Leak in the discharge valve leads to generation of heat Renew the leaky valve

Leak in the safety valve Renew safety valve

Open bypass between suction and discharge Control the bypass to avoid this

6. Evaporator Coil Icing

Another common problem in reefer system is icing of the evaporation coils which may happen
due to:

Reasons Solutions

Too low temperature setting Increase the coil temperature by adjusting TEV or it’s sensor

The coil capacity is less Install large capacity evaporator coils

Defrost is not operational Check if the defrost system is functioning at regular intervals

7. Reduced Cooling Capacity

If the cooling capacity of the plant has reduced and it is not being able to maintain the
provision room or cargo hold temperature, following may be the causes:

Reasons Solutions
Inadequate refrigeration Charge refrigerant in the circuit

Insufficient or damaged insulation in the room Check and renew the insulation

Room or hold is over packed Ensure that the room is not filled above its capacity

Check the functioning of these valves and renew if not

Malfunctioning solenoid or TEV
functioning properly

Place the sensor of the TEV in proper location i.e

Poor thermostat location that senses cold temperatures
discharge of the evaporator

Ensure to close the door while exiting the provision

Room door is kept open
room

8. Reducing oil level in compressor

If the oil level in the compressor crank case of the refrigeration system is reducing within
short intervals, this indicates leakage or increase in consumption of lube oil due to following
reasons:

Reasons Solutions

Ensure that the nozzle in oil return line or filter

Nozzle or filter clogged
in solenoid valve is cleaned and not choked

Foaming of oil may arise due to liquid

Foaming of oil due to liquid in suction line
refrigerant entering the crankcase. Replenish
 oil and troubleshoot cause of liquid in suction

of compressor

The compressor is provided with oil seal at the

Drive side seal leaking drive side. Ensure it is not leaking and renew it

if required

Worn out piston rings/ liner leading to oil carryover in the system Renew the compressor piston rings or liner