Symptom Related Diagnostic Procedures
System Symptoms
There are five basic symptoms associated with air conditioning fault diagnosis. The following conditions are not in order of priority.
Symptom #1
No cooling
Possible Source(s):
- Compressor seized
- Compressor seal failure
- Compressor valve or piston damage
Action(s) to take:
- Renew compressor
Possible Source(s):
- Compressor clutch / circuit faulty
Action(s) to take:
- Refer to PDU
Possible Source(s):
- Drive belt slack I broken
Action(s) to take:
- Adjust or renew
Possible Source(s):
- Blower motor I circuit faulty
- Pressure switch / circuit fault
Action(s) to take:
- Refer to PDU
Possible Source(s):
- Total loss of refrigerant caused by broken pipe or joint
Action(s) to take:
- Repair I renew. Check fault code #23
Possible Source(s):
- Partial loss of refrigerant caused by leaking joint or pipe
Action(s) to take:
- Repair I renew, check fault code #23
Possible Source(s):
- Condenser damage
Action(s) to take:
- Renew, check fault code #23
Possible Source(s):
- Blocked receiver / drier filter
Action(s) to take:
- Renew receiver / drier
Possible Source(s):
- Evaporator sensor / circuit faulty
Action(s) to take:
- Refer to PDU, check fault code #13
Possible Source(s):
- Blocked pollen filter (if fitted)
Action(s) to take:
- Clean or renew
Symptom #2
Insufficient cooling
NOTE: Should a leak or low refrigerant be established as the cause of INSUFFICIENT COOLING, follow the procedures Recovery / Recycle / Recharge, this section, and observe all refrigerant and oil handling instructions.
Possible Source(s)
- Compressor clutch slipping
Action(s) to take:
- Renew clutch assembly
Possible Source(s):
- Flaps or vents closed I seized
Action(s) to take:
- Check fault codes#41 to46
Possible Source(s):
- Blower circuit fault
Action(s) to take:
- Refer to PDU
Possible Source(s):
- Blocked condenser matrix I fins
Action(s) to take:
- Check high /10w side pressures I renew. Check / clean fins
Possible Source(s):
- Blocked evaporator matrix
Action(s) to take:
- Check high 110w side pressures I renew
Possible Source(s):
- Blocked pollen filter (if fitted)
Action(s) to take:
- Clean or renew
Possible Source(s):
- Evaporator temperature sensor faulty
Action(s) to take:
- Refer to PDU
Possible Source(s):
- Partial loss of refrigerant caused by leaking joint or pipe
Action(s) to take:
- Repair/renew
Possible Source(s):
- Blocked expansion valve
Action(s) to take:
- Check high /10w side pressures I renew
Possible Source(s):
- Expansion valve fault
Action(s) to take:
- Check system pressure differential
Possible Source(s):
- Collapsed air conditioning hose hose
Action(s) to take:
- Check high I low side pressures I renew
Possible Source(s):
- Moisture or air in the system
Action(s) to take:
- Check system pressures
Possible Source(s):
- Low refrigerant charge
Action(s) to take:
- Initiate recovery procedure, check fault code #23
Possible Source(s):
Coolant flow valve open
Action(s) to take:
Check operation
Symptom #3
Intermittent cooling
Possible Source(s)
- Compressor clutch slipping
Action(s) to take:
- Renew clutch assembly
Possible Source(s):
- Compressor clutch circuit faulty
- Blower(s) circuit faulty
Action(s) to take:
- Refer to PDU
Possible Source(s):
- Motorized in-car aspirator faulty
Action(s) to take:
- Refer to PDU, check fault code #11
Possible Source(s):
- Evaporator temperature sensor faulty
Action(s) to take:
- Refer to PDU, check fault code #13
Possible Source(s):
- Blocked condenser matrix / fins
Action(s) to take:
- Check high I low side pressures / renew. Check I clean fins
Possible Source(s):
- Blocked evaporator matrix
Action(s) to take:
- Check high 110w side pressures / renew
Symptom #4
Noisy system
Possible Source(s):
Loose or damaged compressor drive belt
Action(s) to take:
- Adjust or renew
Possible Source(s):
- Loose compressor mountings
Action(s) to take:
- Check for damage, tighten to specification if OK
Possible Source(s):
- Compressor oil level low
Action(s) to take:
- Look for evidence of leakage and rectify as required
Possible Source(s):
- Compressor internal damage
Action(s) to take:
- Check for debris, renew compressor and receiver drier
Possible Source(s):
- Blower motor noise
Action(s) to take:
- Renew motor (assuming no fan interference)
Possible Source(s):
- Excessive refrigerant charge
Action(s) to take:
- Check for vibration or 'thumping' in high pressure line; may be witnessed by high pressure on both HIGH and LOW sides. Recover / recharge
Possible Source(s):
- Low refrigerant charge
Action(s) to take:
- Check for 'hissing' at expansion valve; may be witnessed by low HIGH side pressure. Recover / recharge
Possible Source(s):
- Moisture or air in the system
Action(s) to take:
- Check system pressures
Possible Source(s):
- Heater circuit air-lock
Action(s) to take:
- Fill / bleed procedure
Possible Source(s):
- Suction pipe touching bank 1(A) cylinder head (rubber isolator missing)
Action(s) to take:
- Check the pipe cluster for correct fitting
Symptom #5
Insufficient heating
NOTE: Electrical faults may be more rapidly traced using PDU
Possible Source(s):
- Coolant flow valve stuck 'closed'
- Coolant flow valve stuck 'open' allowing recirculation of coolant at engine idle
Action(s) to take:
- Renew valve
Possible Source(s):
- Motorized in-car aspirator seized
Action(s) to take:
- Renew aspirator
Possible Source(s):
- Cool air bypass damper stuck open
Action(s) to take:
- Renew, check fault code #43
Possible Source(s):
- Blocked air inlet I pollen filter
Action(s) to take:
- Check / clean / renew
Possible Source(s):
- Blower speed low
Action(s) to take:
- Check performance range
Possible Source(s):
- Low coolant level
Action(s) to take:
- Adjust as required (verify and correct reason for loss)
Possible Source(s):
- Engine thermostat faulty
Action(s) to take:
- Check engine running temperature
Possible Source(s):
- Heater water pump seized
Action(s) to take:
- Check operation
Possible Source(s):
- Heater matrix blocked
Action(s) to take:
- Renew matrix
Possible Source(s):
- Heater circuit air-lock
Action(s) to take:
- Fill / bleed procedure