472
Modern Refrigeration and Air Conditioning
Locating Compressor Faults
The most expensive service item for a domestic
refrigerator is the replacement of the compressor. The
technician should carefully check for all other electri-
cal and mechanical failures before determining that
the compressor needs replacement. When a compres-
sor is in good condition, the most common reason for
replacement is an electrical fault.
Other electrical problems often mislead a ser-
vice technician into thinking the motor compressor
is at fault. To check a motor compressor, first discon-
nect power to the unit and then clean the outside of
the compressor dome. Then, remove the cover over the
electrical connections. Disconnect the system wiring
from the compressor: relay, capacitors, overload cutout,
and all. Use an ohmmeter to check motor windings for
continuity, shorts, and grounds. Refer to Chapter 14,
Servicing Electric Motors and Controls. If the unit checks
out correctly, connect a starting circuit to the motor
compressor. Use the correct size of capacitors and over-
load cutout. Connect the starting circuit as shown in
Figure 19-26.
If the system starts and operates correctly with
these manual-start electrical connections, the problem
is in the external system. It may be in the wiring, ther-
mostat, relay, or overload cutout. If the internal electri-
cal motor is faulty, the compressor must be replaced. If
the electrical system operates correctly, the compressor
may not be pumping.
The best check of the compressor is its volt-ampere
(watt) reading at normal low-side and high-side pres-
sures. If the volt-ampere reading is below the motor’s
rating, the pump may be worn out.
If the compressor is operating correctly but not
building up pressure, check for internal problems
with the compressor. To check the compressor’s pump-
ing ability, install a piercing valve on the suction line
and attach a compound gauge or the compound gauge
Overload
protection
C
R
S
W
G
B
Starting
switch
Starting
capacitor
High-pressure vapor Low-pressure vapor
High-pressure liquid Low-pressure liquid
Goodheart-Willcox Publisher
Figure 19-26. To test a capacitor-start motor compressor, remove all electrical leads and then connect a test cord as shown. If the
motor compressor operates properly when manually started, the problem is external.