Air Conditioning - PREVOST H3-41 Maintenance Manual

SECTION 22: HEATING AND AIR CONDITIONING
Problem/Symptom
Evaporator fan not
functioning
5.7.1

Air Conditioning

TROUBLE
Low suction pressure and frosting at dryer outlet.
Low Oil Level.
Excessively cold suction line
And
High superheat
Noisy or knocking compressor.
Compressor vibrates excessively.
Low refrigerant level
Suction pressure rises fast after shutdown.
Insufficient air flow.
No flow of refrigerant through expansion valve.
Expansion valve hisses. Bubbles in moisture and
liquid indicator.
Loss of capacity
Superheat too high.
50 PA1621 Maintenance Manual All Series | Revised February 2019
Probable Causes
Circuit breaker CB3 (CB6 on X3
VIP) tripped
Module A54 is not powered or is
faulty
1. Check / reset circuit breaker CB3 (CB6 on
X3 VIP)
2. 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).
3. Check / reset circuit breaker CB5
X3 VIP check CB7
4. Check fuse F67
5. Probe gray connector on module to see if
it is powered.
6. Check / replace condenser power relay
R12 (probe R12 coil power circuit 67,
should be 24 volts).
CAUSE
Clogged filter.
Check for oil leaks and for leaking oil seal. Do not
attempt to check oil level unless system has been
stabilized at least 20 minutes. See oil level
verification.
Loss of contact between the expansion valve
bulb and the suction line or sticking of the
expansion valve.
Improper insulation.
Check for corrosion and clean, repair or replace
the valve.
Check for broken internal parts. Overhaul if
required.
Check and tighten compressor mounting bolts
and belt tension.
Check for refrigerant leaks and add refrigerant as
required.
Check compressor
damage.
Dirty or iced evaporator. Dirty air filter. Blowers
inactive. Clogged ducts.
Filter-dryer is clogged. Remote bulb has lost
charge or expansion valve is defective.
Gas in liquid line. Add refrigerant.
Clogged filter. Obstructed or defective expansion
valve.
Reset superheat adjustment. Check for clogged
Actions
except:
valve for breakage or