Proheat X45–School Bus - Manual (Page 81)

PROHEAT INSTALLATION & SERVICE 5-24
Compressor Mechanical And Electrical Troubleshooting (No code Indicated)
The following material covers the air compressor mechanical or electrical problems
that DO NOT indicate a Code 9. The compressor/fuel pump motor is ground
side switched- there is always voltage at the positive terminal to the motor.
Symptom: Air Compressor runs as soon as power is applied (No code
indicated)
Check: Internal Short in Motor
a) Disconnect compressor/fuel pump motor from internal harness.
b) To check motor condition:
Spare Compressor Motor is Available – Check:
i) Connect spare motor to internal harness and apply power
to heater.
If spare motor does not run, replace the compressor/fuel
pump motor. If the spare motor still runs:
ii) Inspect internal harness wires going to compressor.
Ensure that there is no chaffing or cuts that would provide
a compressor motor ground short.
If internal harness is in good condition, replace PCM.
Spare Compressor Motor is not Available – Check:
i) Plug connector that normally goes to compressor motor
into the blower.
If the blower does not spin when power is applied, this
indicates that there is a short in the compressor motor or
short in the internal harness. Verify root cause by checking
Steps (ii) and (iii).
If the blower spins, this indicates that there is a fault with
the PCM or there is a short in the internal harness. Verify
root cause by checking Step (iii).
ii) Measure resistance between either pin on the connector
going to the motor and the body of the heater
If the resistance is not in the mega-ohm range, replace the
compressor/fuel pump motor.
If the resistance is in the mega-ohm range, go to Step (iii).
iii) Inspect internal harness wires going to compressor.
Ensure that there is no chaffing or cuts that would provide
a motor ground short.
If internal harness is good condition, replace PCM.