On-and-off operation of the expansion valve means that
the receiver-drier is not removing moisture from the
system. These contaminants should cause the moisture
indicator's element to turn white and then pink.
Compressor problems usually show in one of four ways:
abnormal noise; seizure; leakage; or low suction and
Resonant compressor noises are not causes for alarm;
irregular noise or rattles are likely to be caused by
The evaporator coils are basically trouble-free when
airflow over the fins is not blocked. External or, less
often, internal blockages will cause low suction pressure
as well as little or no cooling.
If a leak exists in the system, and it cannot be traced to
other parts or fittings, suspect damage to one of the
evaporator coils. Notify your supervisor.
The condenser is usually trouble-free. Normally, the
temperature of the condenser outlet line is noticeably
cooler than the inlet line. However, when road debris
(such as leaves or dirt buildup) cakes up, airflow over
the condenser fins is blocked; air is not able to absorb
enough heat to turn the hot refrigerant gas into a liquid.
High head pressures will result. In these cases, carefully
clean off the outer surfaces of the condenser with
compressed air or a soap and water solution; be careful
not to bend the fins.
High head pressures will also occur if the condenser's
refrigerant. Frost will appear at the point where the flow
Less common internal blockages (bits of foreign material
or metallic grit build-up) will stop the flow of refrigerant.
A quick test to check that poor system performance is
caused by the condenser is to direct a spray of water
onto the condenser while the system is running. If the
air conditioner cools
better because of the assist provided by the water, it is a
sign that the condenser is not working.
When troubleshooting a suspected condenser problem,
remember that the problem may be caused by the
radiator transferring high levels of heat to the condenser.
IMPORTANT: Before troubleshooting the thermostatic
switch, notify your supervisor to check for a full charge of
refrigerant in the system. The compressor will not
operate, or will cycle too often, if there is not enough
refrigerant in the system.
Quick or delayed cycling of the compressor may be
caused by a thermostatic switch that is working, but is
out of adjustment. If, after doing the tests below, the
switch seems to be out of adjustment, replace it (the
thermostatic switch cannot be recalibrated).
Be sure the compressor clutch is operating
Expose the evaporator coil.
Start the engine. Place the air conditioner control
at its coldest setting; turn on the air conditioner
and the fan.
Place an accurate thermometer in contact with a
tube on the evaporator coil. Be sure the
thermometer is in good contact with the tube, or
you will get a wrong reading.
When the temperature drops below 31 to 36F (-
temperature rises to 39 to 44F (4 to 7C).
If the compressor did not engage when the
temperature was above the accepted high range,
do the following test:
5.1 Connect a voltmeter or a test light from one
of the terminals on the thermostatic switch to
ground. Repeat this test with the other
terminal on the switch.
3-92.2 Change 3