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TM 5-4120-287-15
Probable Cause
Possible Remedy
High-low pressure switch
Check switch; replace if necessary (para 6-6c).
Filter drier clogged
Replace filter drier (para 7-8 and 7-15a).
Defective thermoexpansion valve.
Replace thermoexpansion valve (para 7-21).
Defective hot gas bypass valve.
Replace bypass valve (para 7-20).
Defective liquid quench valve.
Replace quench valve (para 7-19).
Defective charge valve.
Replace charge valve (para 7-14 and 7-16).
Defective pressure release valve.
Replace pressure relief valve (para 7-15).
Defective evaporator.
Replace evaporator (para 5-27).
Defective condenser-subcooler assembly.
Replace condenser-subcooler assembly (para 5-24).
5-8.
Excessive Cooling
Probable Cause
Possible Remedy
Defective thermostat (S105).
Check thermostat. Replace if necessary (para 3-39and 6-6e).
Defective liquid refrigerant solenoid valve. Solenoid
Check for 28vdc across terminals 4 and 5 of terminal board
valve passes refrigerant after coil (L101) is
TB1. Disconnect solenoid coil at TB1. Start up air conditioner
deenergized.
and observe liquid refrigerant sight glass if flow is evident,
replace solenoid valve (para 7-18).
5-9.
Motor Compressor Excessively Noisy
Probable Cause
Possible Remedy
Defective thermoexpansion valve (allowing liquid
Replace thermoexpansion valve (para 7-21).
carryover).
Defective liquid quench valve (allowing liquid
Replace liquid quench valve (para 7-19)
carryover).
Defective motor compressor.
Replace motor compressor (para 5-20).
5-10. Motor Compressor and Condenser Fan Inoperative (All of the components functioning)
Probable Cause
Possible Remedy
Trip relay K101 tripped (energized).
Press SYSTEM RESET switch (S1) (paragraph 6-9c (1)
Condenser discharge door closed.
Open condenser discharge door.
Defective condenser discharge door microswitch(S101)
Check microswitch S101; replace if necessary (para 6-6a).
Remote control harness assembly defective.
Check for continuity between identically marked terminals of
plugs P102 and P103. Repair or replace a defective harness
(para 3-41b).
Low ambient temperature switch closed. High-low
Isolate faulty switch by continuity check at terminals 1
pressure switch closed. Compressor thermal over-
and 2 of terminal board TB1 (fig. 1-9).
load switch closed.
Defective remote control box assembly.
Check remote control box assembly. Replace or repair a
defective remote control box assembly (paragraph 6-3).
Defective trip relay (K101).
Check trip relay (K101), replace if defective (para 6-9c(1)).
5-11. Motor Compressor Inoperative (All other components functioning)
Probable Cause
Possible Remedy
Defective line contactor relay (K104).
Check contactor; replace if necessary (para 6-9c(4)).
Connectors P105 and J105 and/or P113 and J113
Check for security of attachment and integrity of
And/or motor terminals not properly secured;
connector. Check harness. Replace a damaged
connector or wiring harness damaged.
connector or harness assembly.
Defective time delay relay (K102).
Operate air conditioner in cooling mode. After 3 seconds check
for 28vdc across relay K104 terminals X1 and X2. Replace a
defective time relay (para 6-9c (2)).
Defective motor compressor.
Replace motor compressor (para 6-12c, 6-13, and 6-14c).
5-12. Condenser Fan Inoperative (All other components functioning)
Probable Cause
Possible Remedy
Defective line contractor relay (K105).
Check contactor; replace if necessary (para 6-9c(4), and 6-10).
Connectors P106 and J106 and/or P108 and
Check for security of attachment and integrity of
J108 and/or P111 not properly secured or connectors
connectors. Replace a damaged connector.
damaged.
Defective condenser fan motor.
Check condenser fan assembly; replace if necessary
(para 6-11b, 6-13, and 6-14b).
5-3
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