TM 9-4120-357-14
TABLE 4-2. TROUBLESHOOTING (Cont)
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
Step 6. Disconnect each element in turn, and check continuity. Also check continuity of thermostat point
to point. Continuity should exist when temperature is below 142 (61 ).
F
C
Replace faulty heating element or the thermostat.
Step 7. Remove front panel and junction box cover. Tag wires to relays K1 and K2 for identification, and
disconnect. Apply 28 volts dc to terminals X1 and X2 on relay K1, and check continuity of pairs
A1-A2, B1-B2 and C1-C2. Continuity should exist in each pair. Check continuity of each
terminal to ground. Continuity should not exist. Repeat procedure with relay K2.
Replace bad relay.
9. EXCESSIVE NOISE
WARNING
Hearing protection must be worn when maintenance is performed while air condi-
tioner is in operation. Failure to heed this warning can result in hearing loss or in-
jury.
CAUTION
If knocking or hammering is heard when air conditioner is started up, shut down at
once and report the condition to direct support maintenance. The compressor may
be pumping liquid refrigerant, which will cause severe damage.
Step 1. Check evaporator and condenser fan impellers for looseness, vibration or interference.
Tighten setscrews. Check impellers for damage which would cause out-of-balance
condition, and replace impeller. Establish proper clearance between impeller. Establish
proper clearance between impeller and guard, shroud, etc.
Step 2. Check fan and blower motors for wear, as indicated by noisy operation or excessive end- or
side-play.
Replace bearings, or replace motor.
4-14
