TM 9-4120-388-14
5-21. COMPRESSOR (B1) - Continued.
Do not touch heating element.
(4) Carefully feel lower part of compressor.
(a) If air conditioner has been connected to power supply for at least four hours, compressor should feel
warm (100 to 120F) (38 to 49 C). If not warm, test crankcase heater for continuity.
(b) If air conditioner has not been connected to power supply for at least four hours, compressor tempera-
ture should be the same as surrounding air temperature.
(5) Using multimeter, test crankcase heater and thermostat circuit at (J4) connector. Test resistance from pin
F to pin G. Resistance should be 950 to 1430 ohms. Lower reading indicates short, and infinite reading
indicates an open.
(6) Using multimeter, test crankcase heater and thermostat at junction box:
(a) Remove compressor junction box cover.
(b) Open connection between thermostat lead and heater lead.
(c) Check heater continuity between open connection and (J4-)F. If open, heater should be replaced.
(d) Check thermostat continuity between open connection and (J4-G). If open, thermostat should be replaced.
(7) Using multimeter, test compressor motor windings.
(a) Check continuity between pins A, B, and C and the compressor body. No continuity should exist. If
continuity exists, the compressor is bad.
(b) Test 3 phase windings at (J4):
A to B
B to C
A to C
All resistances should be above zero and less than 2 ohms.
(c) Test resistance between pin D and pin E. Resistance should be zero indicating motor protector is
closed.
(d) Compressor containing shorted, open or grounded winding or open motor protector, should be re-
placed.
(e) If compressor windings are bad, check for compressor burn out prior to installing a new compressor.
(See instructions in compressor removal)
b. Heater replacement. (Refrigerant system discharge is not required)
(1) Be sure that the power has been disconnected at the power source and covers have been removed during
access and testing.
Allow heater to cool before touching. Severe burns can result from touching hot
heater.
(2) Tag and disconnect two heater leads from junction box terminals.
(3) Using pliers, remove band on heater.
(4) Spread the heater ends to clear junction box.
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