464
Modern Refrigeration and Air Conditioning
or lead is needed. Operate the switch as explained in
the preceding paragraph.
Safety Note
Capacitor
After testing is completed, remember to short the
testing capacitor using a 20,000 Ω (20 kΩ), 2 W resistor.
This will eliminate the possibility of electrical shock.
The test cord for a capacitor-start, capacitor-run
motor is shown in Figure 19-13. Use new capacitors
of the same rating as the ones on the system being
tested. Close the start switch for one or two seconds
and then open it. If the motor compressor works, check
the electrical system up to the compressor. If the motor
does not operate when tested, further motor checks
are needed. This is explained in Chapter 14, Servicing
Electric Motors and Controls.
Pro Tip
Using Test Cords to Check Continuity
The test cords shown in Figure 19-11, Figure 19-12,
and Figure 19-13 can be used for checking continuity
and grounding by replacing the fuse with a lightbulb.
C apacitor SSafetyyafet
Af ter testing is completed, remember to short the
testin g capacitor usin g a 20,000 Ω ( 20 k Ω ) , 2 W resistor.
This will eliminate the possibility o f electrical shock .
Using Test Cords to Check Continuit y
The t es t cords s hown in Figure 19-1 1 , Figure 19-1 2 ,
an d Figure 19-1 3 can be used f or checking continuity
and grounding by replacing the f use with a lightbulb.
Ineffective cooling problems can be caused by
the evaporator fan motor or the condenser fan motor.
A test cord like the one shown in Figure 19-14 can be
used to directly test a fan motor. These motors are usu-
ally replaced if they are found to be faulty.
Pro Tip
Fan Motor ReplacementtlacemenpRe
Before removing a fan from a motor shaft, put match-
ing marks on the fan hub and the shaft. This ensures that
the fan is positioned correctly on the new shaft.t.f
Electrical failure in the mullion heater may cause a
door gasket to freeze to the cabinet. The heater must be
checked for continuity with a test light or an ohmmeter.
Locate the circuit in the wiring diagram. Disconnect
both ends of the mullion heater leads. Then, test the
heater for continuity.
If the mullion heater is defective, look for a second
(extra) heater in the insulation. Most cabinets have one.
Test it also, and connect it if it has continuity. If there is
no extra heating unit, install one of the same wattage
(volt-ampere) rating.
If the problem is a faulty wire, use a stiff steel wire
to pull new wiring through the foamed-in-place insu-
lation. If necessary, drill a hole (up to 1/2″) in the back
F an Motor
Before removing a fan from a motor shaft, put match-
i ng marks on the f an hub and the sha ft. This ensures that
the f an is positioned correctly on the new sha
Fuse
Start/run switch
1
2
3
4
A. W. Sperry Instruments, Inc.
Figure 19-11. A manual start test cord arrangement for hermetic compressors. Clip 1 attaches to the compressor’s common terminal.
Clip 2 attaches to the run terminal. Clip 3 attaches to the start terminal. Clip 4 attaches to the ground.
0 0
3
Start capacitor
Fuse
Start/run switch
1
2
4
A. W. Sperry Instruments, Inc.
Figure 19-12. Test cord arrangement for a capacitor-start, induction-run motor. Clip 1 attaches to the common winding terminal. Clip 2
attaches to the run winding terminal. Clip 3 attaches to the start winding terminal. Clip 4 attaches to the ground.