Proheat X45–School Bus - Manual (Page 80)

5-23 SECTION 5. TROUBLESHOOTING & REPAIR
The X45 fuel gear pump is driven by the same motor as the compressor.
Therefore, there is NO fuel pump electrical diagnostic code. A FUEL PUMP
diagnostic code would indicate a fault in the PCM only.
A short or open circuit fault in the motor that drives the fuel pump will be
indicated by a COMPRESSOR diagnostic code.
8 Fuel Pump
A COMPRESSOR 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.
Symptom: Air Compressor not running (code indicated)
Check: Air Compressor wiring & function
a) That compressor 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 compressor. If it tests OK replace PCM.
(See Figures 5-7 & 5-8 and Test Procedure)
Test Procedure:
a) Connect air compressor directly to a power source
of the rated voltage (12/24 Volts) and see if the motor runs.
If not, replace the compressor.
b) Measure air compressor motor resistance. Use a multimeter
to measure the resistance across the compressor connector
pins. If resistance shows an open or short circuit, replace the
compressor assembly.
c) Measure air compressor current. Use test lead part #967921K,
as described on Service Bulletin #967329 in the Appendix.
Figure 5-21 Compressor Test
MODEL CURRENT DRAW (Amps)
X45-12 3.50 - 5.00 @ 12 Volts
X45-24 1.50 - 3.00 @ 24 Volts
PRESSURE
ADJUSTING
SCREW
9 Compressor