TM 9-4120-371-14
a. Inspection/Test
(1) Be sure power has been disconnected from air conditioner.
(2) Electrically test the heater element, heater thermostat, wiring harness, and motor as follows.
(3) Disconnect wiring harness at connectors P4 and J4 (located on the compressor junction box).
(4) Carefully feel lower part of compressor.
If air conditioner has been connected to power supply for at least four hours, compressor
should feel warm (100 to 120F). If not warm, test crankcase heater for continuity.
If air conditioner has not been connected to power supply for at least four hours, compressor
temperature should be the same as surrounding air temperature.
(5) Using multimeter, test crankcase heater and thermostat circuit at J4 connector:
Using multimeter, test resistance from pin F to pin G. Resistance should be 950 to 1450 ohms,
Lower reading indicates short, and infinite reading indicates an open.
*(6) Using multimeter, test crankcase heater and thermostat at junction box:
Remove compressor junction box cover.
Open connection between thermostat lead and heater lead.
Check heater continuity between open connection and J4F. If open, heater should be
replaced.
Check thermostat continuity between open connection and J4G. If open, thermostat should be
replaced.
(7) Using multimeter, test compressor motor windings.
Check continuity between pins A, B, and C and the compressor body. No continuity should
exist. If continuity exists, the compressor is bad.
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.
Test resistance between pin D and pin E. Resistance should be zero indicating motor protector
is closed.
Compressor containing shorted, open or grounded winding or open motor protector, should be
replaced.
If compressor windings are bad, check for compressor burn out prior to installing a new
compressor. (See instructions in compressor removal.)
*Effective for Carrier Compressor.
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