Proheat X45–School Bus - Manual (Page 87)

PROHEAT INSTALLATION & SERVICE 5-30
A BLOWER diagnostic code indicates an open circuit in the wire harness, a short
in the wire harness between the positive and negative leads or an internal
short in the motor. This component is ground side switched in the PCM.
The PCM measures the RPM of the blower. This feature will give an error should
it fall below the necessary RPM to maintain sufficient combustion air.
Symptom: Blower not running (code indicated)
Check: Blower wiring & function
a) That blower is connected to harness correctly.
(See PROHEAT Wiring Diagram page 1-4)
b) The connector pins for damage or corrosion.
c) Harness for pinched or abraded wires.
d) Test blower. If it tests OK replace PCM.
(See Figure 5-25 and Test Procedure)
Blower Mechanical and Electrical Troubleshooting (No code Indicated)
This section covers the blower mechanical or electrical problems that do not
indicate a Code 12. The blower motor is ground side switched — there is
always voltage at the positive terminal to the motor.
Symptom: Blower runs as soon as power is applied (No code indicated)
Check: Internal Short in Motor
a) Disconnect blower motor from internal harness.
b) To check motor condition:
Spare Blower is Available – Check:
i) Connect spare blower to internal harness and apply power
to heater.
If spare blower does not run, replace the blower pump. If the
spare blower still runs:
ii) Inspect internal harness wires. Ensure that there is no
chaffing or cuts that would provide a blower motor ground
short.
If internal harness is in good condition, replace PCM.
Spare Blower is not Available – Check:
i) Plug connector that normally goes to blower motor into
the coolant pump.
If the coolant pump does not spin when power is applied,
this indicates that there is a short in the blower motor or
short in the internal harness. Verify root cause by checking
Steps (ii) and (iii).
If the coolant pump 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 blower motor and the body of the heater
If the resistance is not in the mega-ohm range, replace the
blower.
If the resistance is in the mega-ohm range, go to Step (iii).
12 Blower
CAUTION
When a blower fails, the combustion
chamber must be checked for carbon
build up and cleaned as necessary.