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 indicators element to
turn white and then pink.
Compressor problems usually show in one of four
ways: abnormal noise; seizure; leakage; or low
suction and discharge pressures.
Resonant compressor noises are not causes for
alarm; irregular noise or rattles are likely to be
caused by broken parts. To check for seizure, de-
energize the magnetic clutch and see if the drive
plate can be turned. If it wont turn, the
compressor has seized.
Low discharge pressure may be caused by not
enough refrigerant, not enough belt tension, or a
blockage somewhere in the system. These things
s h o u l d b e c h e c k e d b e f o r e s e r v i c i n g t h e
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.
The condenser is usually trouble-free. Normally,
the temperature of the condenser outlet line is
noticeably cooler that 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
condensers tubing is abnormally bent, blocking
the flow of refrigerant. Frost will appear at the
point where the flow is restricted.
Less common internal blockages (bits of foreign
material or metallic grit build-up) will stop the flow
A q u i c k t e s t t o c h e c k t h a t p o o r s y s t e m
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
When troubleshooting a suspected condenser
problem, remember that the problem may be
caused by the radiator transferring high levels of
heat to the condenser. Refer to the radiator
section for cooling system troubleshooting.
IMPORTANT: Before troubleshooting the thermo-
static switch, be sure there is 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).
1. Be sure the compressor clutch is operating
2. Expose the evaporator coil.
3. 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
36°F (-1° to 2°C), the compressor clutch
should disengage and remain this way until
the temperature rises to 39° to 44°F (4 to
5. If the compressor did not engage when the
temperature was above the accepted high
range, do the following test:
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