300Tdi Discovery
82
AIR CONDITIONING
2
FAULT DIAGNOSIS
REFRIGERATION SYSTEM FAULTS
For any refrigeration system to function properly all
components must be in good working order. The unit
cooling cycle and the relationship between air
discharge temperature and ambient temperature and
the pressures at the compressor can help to
determine proper 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
conditioner.
The low and high side pressures at the compressor
will vary with changing ambient temperature, humidity,
in-car temperature and altitude.
The following items should be checked before
operating the system:
1. Compressor drive belt tension.
2. Compressor magnetic clutch operation.
3. Condenser fan operation.
4. Condenser fins, dirt will cause poor cooling and
higher operating temperatures.
The following conditions should be checked after
operating the system for several minutes:
1. All high pressure lines and components should
be hot to the touch.
2. All low pressure lines should be cool to the
touch.
3. Inlet and outlet temperatures at the receiver/drier
should be at the same temperature (warm). Any
very noticeable temperature difference indicates
a blocked receiver/drier.
4. Heavy frost on the inlet to the expansion valve
may indicate a defective valve or moisture in the
system.
5. Evaporation air temperature will vary with
ambient temperature and humidity. As humidity
increases the outlet temperature will be higher.
