TM 9-4120-357-14
TABLE 4-2. TROUBLESHOOTING (Cont)
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
Step 5. Remove front access panel and junction box cover, and expose relay, K8, controlling evaporator
fan motor. Tag wires for identification, and disconnect from relay K8. Apply 24-28 volts dc to
terminals X1 and X2, and check continuity of pairs A1-A2, B1-B2 and C1-C2, using an
Replace bad relay.
Step 6. Check continuity of electrical leads from relay K8, terminals A2, B2 and C2 to connector P15,
terminals A, B and C. If leads all indicate continuity. Motor is bad.
Replace faulty motor.
Step 7. If continuity of electrical leads in Step 6 is not indicated isolate the faulty lead by checking
continuity from relay K8 terminals A2, B2 and C2 to connector J10, terminals U, V and I.
Continue checking continuity if necessary, from connector P10, terminals U, V and I to connector
J3, terminals C, D and E, and in turn to connector J9, terminals A, B and C, and finally in turn to
connector P15, terminals A, B and C until the faulty electrical lead is isolated.
Replace faulty electrical lead.
Step 1. Make sure that power cable is connected, that circuit breaker is reset, that mode selector switch
is set at cool and that temperature control thermostat is set at full decrease.
Set controls properly.
Step 2. Check condition of high- and low-pressure cutout switches by pressing reset buttons. Report
failure to direct support maintenance if condition continues and no other corrective action is
effective.
WARNING
Disconnect power from the air conditioner before doing maintenance work on the
electrical system. The voltage used can be lethal.
Step 3. Check for loose electrical connections or faulty wiring.
Tighten loose connections. Replace bad wiring.
Step 4. With front access panel and junction box cover removed, disconnect transformer leads from fuse
block, XF1, terminals 2 and 4. Also disconnect transformer secondary leads from rectifier-filter,
cr, terminals 1 and 4. Apply 208 volts, ac, to input leads which were disconnected from fuse
block. Check voltage at secondary leads to be sure it is 28-30 volts ac.
Replace faulty transformer.
Step 5. With front access panel and junction box cover off, disconnect rectifier-filter leads from fuse
block XF2, terminal 1, and from terminal block TB2, terminal 1. Apply power to transformer to
obtain 27-30 volts ac to rectifier filter, and check disconnected leads to be sure that 24-28 volts
dc is indicated. Positive (+) terminal is at XF2, terminal 1; negative (-) terminal is at TB2,
terminal 1.
Replace faulty rectifier-filter.
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