Common Faults and Simple Detection
1. Undercharge: low discharge gauge reading, lack of frost on
suction pipe, lengthy running times.
2. Air in system: high discharge gauge reading (assuming
sufficient vapour), jumping of gauge pointers, inefficient
working.
3. Dirty condenser or insufficient cooling water: high discharge
gauge reading and incorrect condenser temperature
differentials.
4. Overcharge: unlikely, but gives high discharge gauge reading
and very sensitive expansion valve working.
5.0il on cooling coils: incorrect condenser and evaporator
temperature differentials (oil is an insulator), excess frost on
suction pipe.
6. Choked expansion valve: caused by dirt or freeze up by
water, gives starving of evaporator and rapid condenser
pressure rise.
7. Short cycling: condenser coolant discharge cut outs, choked
expansion cut outs, etc.
8. 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 the
Defective oil pressure cut out
defective cutout
If the defrost timer is getting activated frequently, leading to cutout of
Defrosting timer is getting activated frequently
compressor, check and repair defrost timer
This can be because of leakage of lube oil from seal or carry over of oil.
The lube oil level is below required level
Rectify the leakage and refill the oil level
Foaming of oil leading to reduced oil
Ensure no foaming takes place, renew the oil if required
pressure
Motor overload cutouts are activating Ensure that electrical motor trips are working properly
9. 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 Check and change the
high or LP cutout is set too low setting to advisable limit
Change the setting and
Differential Setting Span is Small: The low pressure (LP) cut out is provided with
increase the span between
starting and stopping pressure setting. If the setting span is too small, it will lead to
starting and stopping
frequent cut-in and cut-out of the compressor
compressor pressures.
Defective Valves: If the compressor discharge valve is leaky or the line solenoid
Replace all the defective
valve is not closing properly, this will lead to variation in sensor pressure and result in
valves
frequent cut-in and cut-out of compressor
Clogged Suction Filters: Compressor is provided with a filter in the suction line. If
Clean the filter
that is clogged, it will lead to frequent LP cut out
10. 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 valve is working
Refrigerant not sufficient for cooling evaporator
properly and clean the filters inside TEV
Thermostat low pressure cut-out not activated at low
Correctly set the LP cut-out to correct setting
temperature/ pressure
Check for leakage of refrigerant and charge with
Refrigerant charge is low in the circuit
required refrigerant
12. 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
The capacity control setting is too high,
Reduce the capacity control setting
leading to knocking sound during starting
The oil pressure is low Ensure that the oil level is maintained and no foaming of
oil is developed. Replenish or refill the lube oil if required
Incorrect alignment of compressor and Check the alignment and set motor and compressor in on
motor line
Ensure that the compressor foundation is secured and all
Loose foundation
foundation bolts are checked for tightness
Ensure to check the elasticity of the belt and renew if the
Loosening of driving belt
belt is slack
13. 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 quantity in the circuit.
Excessive suction temperature Ensure TEV is set properly and
due to less refrigerant in the supplying enough to the evaporator,
circuit else degree of superheat will result in
increase of suction and discharge
temperatures of the compressor
Leak in the discharge valve leads Renew the leaky valve
to generation of heat
Leak in the safety valve Renew safety valve
Open bypass between suction and
Control the bypass to avoid this
discharge
14. Evaporator Coil Icing
Another common problem in reefer system is icing of the
evaporation coils which may happen due to:
Reasons Solutions
Increase the coil temperature by adjusting
Too low temperature setting
TEV or it’s sensor
The coil capacity is less Install large capacity evaporator coils
Check if the defrost system is functioning at
Defrost is not operational
regular intervals
15. 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
Check and renew the insulation
the room
Ensure that the room is not filled
Room or hold is over packed
above its capacity
Check the functioning of these
Malfunctioning solenoid or TEV valves and renew if not
functioning properly
Place the sensor of the TEV in
Poor thermostat location that senses
proper location i.e discharge of
cold temperatures
the evaporator
Ensure to close the door while
Room door is kept open
exiting the provision room
16. 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 in
Nozzle or filter clogged
solenoid valve is cleaned and not choked
Foaming of oil may arise due to liquid refrigerant
Foaming of oil due to liquid in suction line entering the crankcase. Replenish oil and troubleshoot
cause of liquid in suction of compressor
The compressor is provided with oil seal at the drive
Drive side seal leaking
side. Ensure it is not leaking and renew it if required
Worn out piston rings/ liner leading to oil
Renew the compressor piston rings or liner
carryover in the system
