| Malfunction (symptoms) |
Probable causes |
Corrective Action (Remedies) |
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| APU Engine operating at normal speed but no AC power available in coach |
Control relay K1 in power control relay (contactor) box defective |
Replace relay K1 |
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Contactor (power relay) K2 coil defective |
Replace. |
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APU generator defective |
Troubleshoot and repair or replace. |
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| Service line connected to external AC power but no AC power available in coach |
Control relay K1 Defective |
Replace relay K1 |
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Contactor (power relay) K3 coil defective |
(Same as for above relay K2) |
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Plug prongs not fully inserted in receptacle |
Fully insert prongs in receptacle |
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Open circuit in line |
Disconnect and inspect line insulation for cuts or breaks; replace. |
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| APU will not crank with switch on domestic panel in START position |
Automotive battery weak or terminals corroded / loose |
Recharge or replace if defective; clean and tighten terminals |
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20 amp fuse on converter 12 VDC bus blown |
Check and repair circuitry; replace fuse |
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Domestic batteries weak or terminals corroded or loose |
Attempt start with switch on APU; if APU starts Okay then accomplish recharge or replace domestic batteries |
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APU start relay leads not properly connected to terminals |
Tighten terminal nuts |
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| APU cranks with switch in Start position but engine fails to start |
Faulty iginition system |
Troubleshoot and repair. |
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Faulty fuel system |
(Same as previous) |
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Low oil pressure switch preventing start due to lack of oil. |
Check oil level; service as necessary. |
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| Battery condition meter on domestic panel indicates low charge on domestic batteries |
Excessive use of batteries in lieu of APU service line operation of converter |
Slow charge batteries and instruct owner to better utilize APUT and or service line power to provide DC power from converter |
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| Same as above except no reading obtained |
Blown 20 or 50 amp fuse at converter bus. |
"Check causes |
repair and replace blown fuse." |
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Cable clamps at terminal posts loose or corroded |
Clean and tighten |
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| Battery electrolyte level consistently found low during periodic checks |
Excessive alternator output (automotive) |
"Replenish battery |
then adjust regulator" |
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Cracked or leaking battery case (container) |
"Visually inspect battery; if cracked |
replace." |
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"Excessive converter output could also cause this malfunction. If trouble is isolated to converter |
replace converter." |
"Care should be taken |
in the even battery case is cracked or leaking |
to protact hands from electrolyte. A suitable pair of rubber gloves (not the household type) should be worn when removing the battery by hand. It is recommended that a battery carrying strap be used whenever the battery is to be removed from the coach." |
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| Converter inoperative with AC power applied |
20 amp fusibles unit in circuit breaker box fuse blown (Q-light adjacent to fuse holder illuminated) |
Check converter right side AC power supply circuit for short or overload; repair and replace fuse. Replace converter |
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