Hvac Electrical System Troubleshooting - PREVOST H3-41 Maintenance Manual

SECTION 22: HEATING AND AIR CONDITIONING
5.7

HVAC ELECTRICAL SYSTEM TROUBLESHOOTING

Always check DID for electrical faults before performing repairs. Address any modules not
responding and take corrective action. This should be the first step in troubleshooting.
Problem/Symptom
No temperature control in the
passenger area
Passenger temperature
display indicates two dashes
"--"
Defroster fan not functioning
HVAC condenser fans not
functioning
48 PA1621 Maintenance Manual All Series | Revised February 2019
Probable Causes
Problem with the temperature
sensor located in the
passenger's area return air duct
or the sensor wiring
Module AE47 is not powered or
is faulty
Module A24 is not powered or is
faulty
Module A30 is not powered or is
faulty (H3 VIP & X3 VIP only)
Circuit breaker CB7 (CB5 on X3
VIP) tripped
Seized bearing
Bad wiring
Module A54 is not powered or is
faulty
Actions
1. Instruct the driver to manually control the
temperature by playing with the passenger
set point. Set above 22°C (72°F) to heat
and below 22° C (72°F) to cool
2. Check the Diagnostics menu of the Driver
Information Display (DID). Select Fault
Diagnostics and Electrical System. The
message "No Response ModA47 (or
ModA24), Active"
problem on the module. (A CAN network
problem would show the same message
but doesn't produce these symptoms).
3. Check / reset circuit breaker CB1(CB3 on
X3 VIP)
4. Check fuse F16
5. Probe gray connector on module to see if
it is powered.
1. Check / reset circuit breaker CB7(CB5
on X3 VIP)
2. Check/reset CB15, CB16, CB17,
CB18 on HVAC control module
3. Check / replace condenser power
relay R10 (probe R10 coil power
circuit 67A, should be 24 volts).
4. Check the Diagnostics menu of Driver
Information Display (DID). Select
Fault Diagnostics and Electrical
System. The message "No Response
ModA54, Active" indicates a power
problem on the module. (A CAN
network problem would show the
same message but doesn't produce
this symptom).
5. Check fuse F67
Check CB5 except: X3 VIP check
CB7
indicates a power