Refrigerant System Faults

For any refrigeration system to function efficiently all components must be in good working order. The system cooling cycle and the relationship between air discharge temperature and ambient temperature and the pressures at the compressor can help in determining the correct operation of the system. The length of any cooling cycle is determined by such factors as ambient temperature and humidity, thermostat setting, compressor speed and air leakage into the cooled area, etc. With these factors constant, any sudden increase in the length of the cooling cycle would be indicative of abnormal operation of the air conditioning system.

The low and high side pressures at the compressor will vary with changing ambient temperature, humidity, in-car temperature and altitude.

Where the efficiency of the refrigerant system is suspect, carry out a system performance test. See Adjustment. A/C System Performance Test
The following components should be checked before operating the system:
- Drive belt tension.
- Compressor clutch operation.
- Blower motor operation.
- Condenser unit fins. Build up of dirt will cause poor cooling and higher operating temperatures.
- Air filter elements. A blocked filter will restrict cooling of the evaporator and it is, therefore, important to renew both filters at the recommended service schedule.

The following conditions should be checked after operating the system for several minutes:
- All high pressure lines should be hot to the touch.
- All low pressure lines should be cool to the touch.
- Inlet and outlet temperatures at the receiver/drier should be at the same temperature (warm). Any noticeable temperature difference would indicate a blocked receiver/drier.
- Heavy frost on the expansion valve inlet would indicate a defective valve or moisture in the system.

Symptom - High Head Pressure

POSSIBLE CAUSE
- Overcharge of refrigerant.
REMEDY
- Discharge, evacuate and recharge system.
POSSIBLE CAUSE
- Air in system.
REMEDY
- Discharge system, fit new receiver/drier, evacuate and recharge system.
POSSIBLE CAUSE
- Condensor air passage blocked with dirt etc.
REMEDY
- Clean condenser of debris.
POSSIBLE CAUSE
- Condenser fan motor/s defective.
REMEDY
- Renew motor/s.
POSSIBLE CAUSE
- Loose compressor drive belt.
REMEDY
- Check drive belt tensioner or renew drive belt.
POSSIBLE CAUSE
- Seized compressor.
REMEDY
- Renew compressor.

Symptom - Low Head Pressure

POSSIBLE CAUSE
- Undercharge of refrigerant.
REMEDY
- Evacuate and recharge system.
POSSIBLE CAUSE
- Leaking compressor valves.
REMEDY
- Renew compressor.
POSSIBLE CAUSE
- Defective compressor.
REMEDY
- Renew compressor

Symptoms - High Suction Pressure

POSSIBLE CAUSE
- Loose drive belt.
REMEDY
- Check drive belt tensioner or renew drive belt.
POSSIBLE CAUSE
- Refrigerant flooding through evaporator into suction line; evident by ice on suction line.
REMEDY
- Renew expansion valve.
POSSIBLE CAUSE
- Expansion valve stuck open.
REMEDY
- Renew expansion valve.
POSSIBLE CAUSE
- Leaking compressor valves.
REMEDY
- Renew compressor.
POSSIBLE CAUSE
- Receiver/drier blocked; evident by temperature difference between input and output lines.
REMEDY
- Fit new receiver/drier, evacuate and recharge system.

Symptoms - Low Suction Pressure

POSSIBLE CAUSE
- Expansion valve sticking or closed.
REMEDY
- Clean or if renew if necessary.
POSSIBLE CAUSE
- Moisture freezing in expansion valve orifice. Valve outlet tube will frost while inlet tube will have little or no frost.
REMEDY
- Fit new receiver/drier, evacuate and recharge system.
POSSIBLE CAUSE
- Debris restricting external air intake grille.
REMEDY
- Clean air intake grille.
POSSIBLE CAUSE
- Blocked air inlet housing filters.
REMEDY
- Renew air filters.
POSSIBLE CAUSE
- Defective blower motor/s, blown fuse/s or loose electrical connections.
REMEDY
- Check and renew fuses 42 or 43, tighten all relevant wiring connections or renew blower motor/s.

Symptom - Noisy Expansion Valve (Steady hissing)

POSSIBLE CAUSE
- Low refrigerant charge.
REMEDY
- Test system for leaks; renew components as required.


Symptom - Insufficient Cooling

POSSIBLE CAUSE
- Expansion valve not operating efficiently.
REMEDY
- Renew expansion valve.
POSSIBLE CAUSE
- Low refrigerant charge.
REMEDY
- Test system for leaks. Evacuate system and renew components as required. Recharge system.
POSSIBLE CAUSE
- Compressor not pumping.
REMEDY
- Renew compressor.