Refrigerator Vapour Compression Systems Troubleshooting

Visual fault finding

Compressor not running

1. Main supply isolator open.
2. Fuse blown.
3. Overload open circuit.
4. Control circuit open (low pressure switch, high pressure switch or thermostat).

Fixture temperature too high

1. High evaporator load.
2. Defrost heater(s) energized.
3. Condenser blocked with dirt.
4. Restricted air flow over the condenser or restricted water flow.
5. Condenser fan inoperative.
6. Evaporator blocked with ice.
7. Evaporator fan inoperative.
8. Vapour bubbles in sight glass (possible shortage of refrigerant).
9. Frosting liquid line (blocked drier).
10. Broken or loose drive belts.
11. Expansion valve bulb loose on suction line or broken capillary.

System noisy

1. Evaporator/condenser fan blades touching fan guards or loose on the motor shaft.
2. Compressor oil sight glass empty (shortage of oil or oil entrainment).
3. Compressor head frosted (compressor pumping liquid refrigerant).
4. Loose motor pulley, compressor flywheel, compressor mountings.


If the fault is not obvious after visual inspection:
1. Attach compound and pressure gauges.
2. Check that the compressor is pumping.
3. Observe operating pressures.

High discharge pressure

1. Overcharge of refrigerant.
2. Air in the system.
3. Dirty condenser, poor air supply.
4. Inadequate water flow.
5. High load imposed on the evaporator.

Low discharge pressure

1. Shortage of refrigerant.
2. Compressor inefficient.

High suction pressure

1. Compressor inefficient.
2. Overcharge of refrigerant (capillary systems only).
3. Expansion valve defective.
4. High evaporator load.
5. Defrost system operating when compressor is running.

Low suction pressure

1. Shortage of refrigerant.
2. Blocked or defective expansion valve.
3. Blockage in liquid line, drier solenoid valve or shut-off valve.
4. Blocked evaporator (excessive ice build-up).
5. Inoperative evaporator fan.
6. Defective water pump or blocked water filter on a chiller system.

Leave a Reply

Your email address will not be published. Required fields are marked *