Chapter 15 Refrigeration System Diagnosis and Leak Detection 239
Note: On receiver-drier systems, if the
receiver-drier is hot to the touch, the
expansion valve is defective or plugged.
If the receiver-drier is cool, the receiver-drier is
defective.
Defective Compressor
After the engine and refrigeration system have been
operating for fi ve minutes, observe and listen to the com-
pressor. Watch the clutch operation carefully. When the
outside temperature is low, (60°F or 16°C) the clutch may
cycle every 20 seconds. When the air temperature is high
(90°F or 30°C), the clutch may cycle every one or two min-
utes or more. On very hot and humid days, the clutch may
not cycle. On a vehicle with an evaporator control valve,
the clutch should remain engaged. If the clutch cycles
excessively, the system may have a low charge.
Some compressor problems are easy to diagnose. A
noisy compressor has usually failed or is about to fail. If the
compressor will not turn or makes an extremely loud noise
when engaged, it may be seized. Adding oil to the refrig-
eration system can sometimes quiet older compressors.
Other compressor problems are more diffi cult to
detect. Diagnosing internal compressor problems requires
skill at reading gauge pressures, Figure 15-16. Variable
displacement compressors are sometimes diffi cult to diag-
nose as some of them are able to adjust pressure so that
even a system restriction would cause only a very minor
pressure change. Usually, a good indicator of possible
internal compressor problems is slightly lower than normal
high side pressure with a confi rmed full system charge.
However, before the compressor is suspected, the system
should be checked for restrictions and proper refrigerant
charge.
Defective or Restricted Condenser
A defective condenser will usually show up as a leak,
allowing the refrigerant charge to escape. Because the
condenser handles high refrigerant pressures, a leak will
usually be evident, even without the use of a leak detector.
However, a slow leak from the condenser will allow refrig-
erant oil to escape, possibly leading to compressor failure.
Restrictions in the condenser can be either internal
or external. An internal restriction will create higher than
normal gauge pressure readings, Figure 15-17. In some
cases, a restriction may cause ice or frost to form on the
condenser. An external restriction will cause higher than
normal gauge readings due to the lack of air passing through
the condenser.
Defective or Restricted Evaporator
A defective evaporator will usually show up as inad-
equate cooling caused by a leak in the core. A restriction in
the evaporator may cause ice to form on the high pressure
tube leading to the evaporator. Both problems will cause
lower than normal system pressures.
Defective or Misadjusted Switch
A defective pressure or thermostatic switch can also
cause problems. Usually, problems caused by one of
Figure 15-16. Gauge readings for a defective compressor.
Defective Compressor
Low Side (Suction)
Symptoms: Poor to no cooling, continuous compressor operation (orifice tube systems),
sight glass clear. System pressure equalilzes very fast when system is turned off.
Note: Confirm system charge.
Orifice Tube
Exp. Valve
VDOT
(Varies with ambient temperature) (Varies with ambient temperature)
High
Normal to High
Normal to High
Low
Low
Low
High Side (Discharge)
0
1
0
20
30
40
50
60
70
80
90
100
110
120
0
50
100
150
200
250
3
00
350
400
450
500