Electrical Maintenance (Rev 1/99)
52
When the unit is inoperative, follow a systematic checking
sequence. This will save time and eliminate guesswork.
Check the power cable receptacle for power. If power is
present, check for power at the unit terminal board.
Check for control circuit power at the circuit breaker. If the
contactor is pulled down but the compressor motor fails to
start, the trouble is probably in the compressor motor
assembly.
12 Volt System
The dc voltage should be 12.5 to 13 volts and the current
through the 2R wire should be less than 25 amps. If the cur-
rent is less than 25 amps and the voltage is less than 12
volts:
1. Check the ac line voltage the transformer fuse. The line
voltage must be at least 90% of the voltage specified
for the unit. if the ac line voltage is acceptable and the
transformer fuse is intact, go to step 2.
2. Measure the transformer output voltage (ac) at the rec-
tifier between wires X1 and X4. If the transformer out-
put voltage is between 12 to 13 volts ac no load, it is ok.
If the transformer output voltage is acceptable, go to
step 3.
3. Check the rectifier output voltage (dc) on the 2R wires
at the terminal board.
If the rectifier output voltage is less than 13 Vdc and
the load is not excessive (not more than 25 amps), the
rectifier is defective.
EVAPORATOR HEATERS (Optional)
Test the resistance of each evaporator heater by disconnect-
ing it from the circuit and checking it with an ohmmeter.
The resistance of each heater should be approximately 70
ohms.
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