462
Modern Refrigeration and Air Conditioning
or the compressor motor is not running or is running
erratically. The following sections provide some sug-
gestions for troubleshooting the system based on each
of those conditions:
Compressor Runs, but Cabinet Temperature Is
Incorrect
• Check for cabinet leaks.
• Check for evaporator icing.
• Check for good air circulation over the condenser.
• Check for dirt or dust buildup on the condenser.
• Check the temperature control systems.
• Check the internal operation of the system.
Compressor Does Not Run, or Runs Erratically
• Problems may be in the external circuits of
the refrigerator; eliminate external electrical
components as a possible cause first.
• Check the motor.
19.3 Checking External Circuits
It is important to locate the trouble and determine
the cause accurately. Sometimes expensive compres-
sors are needlessly replaced because they are believed
to be faulty. The real trouble, however, may be in
less expensive and easily repaired external devices.
Always eliminate external components and wiring as
a source of problems before diagnosing and replacing
internal components.
Problems in refrigerator-freezers are frequently
caused by failures in the wiring or auxiliary systems.
Common sources of problems include the following:
• Power-in connections.
• Thermostat.
• Wire terminals.
• Relays.
• Capacitor (if the unit has one).
• Defrost timer.
Each of these devices should be checked carefully
before the compressor or core refrigeration system
components are suspected. These parts can be checked
best by removing them from the wiring system. After
they are isolated from the rest of the system, the parts
can be checked independently. As an alternative, each
part can be temporarily replaced by a test part of the
proper size or capacity and known to be in good work-
ing order. Also make sure the wiring going to each
component is not cut, damaged, or disconnected. The
refrigerator-freezer can then be checked to see if it
operates properly.
Pro Tip
Inspecting Electrical Connectionss
Electrical connections must be clean and tight. If
loose or dirty, they often overheat. Excessive tempera-
tures can discolor the connection. The connection may
be darkened by oxidation. A blue or greenish tint indi-
cates overheating and corrosion. If the surrounding insu--
lation is charred, overheating has occurred..d
The thermostat should be connected into the hot
wire of the circuit. This wire has black insulation. The
other wire is called the common wire of the circuit. It
has white insulation. It should be run directly to the
motor. The common wire carries the same amount of
current as the black wire.
A system of green grounding wires grounds all
electrical components in a refrigerator or freezer. This
ground is not a current-carrying wire. It is for safety
only. It is used to avoid an electric shock if a short cir-
cuit occurs in the electrical system.
Troubles such as open circuits and shorts to
ground are easily checked with a multimeter. A test
cord can be used to check four-pole motors. However,
two-pole motors should be tested only by using a
properly sized relay in the circuit. These motors overheat
if the starting circuit is connected for more than two or
three seconds.
Inspectin g Electrical Connection
Electrical connections must be clean and tight. I f
l oose or dirty, they of ten overheat. Excessive tempera-
tures can discolor t h e connection. Th e connection ma y
be darkened by oxidation. A blue or g reenish tint indi-
cates overheating and corrosion. I f the surrounding insu
lation i s charred, overheating h as occurre
A B
Goodheart-Willcox Publisher
Figure 19-9. Two ways to reduce noise caused by vibrating
tubing. A—Wrap tape around the tubing where the tubing
touches the cabinet. B—Put tape or a rubber block on the
tubing in the center of a vibrating section.