Heater Core and Defroster Diagnosis
Insufficient, Erratic, or No Heat or DefrostPossible Source(s):
- Coolant leaks
Action(s) to Take:
- Check radiator cap pressure. Replace if below minimum pressure. Fill coolant to correct level. Pressure test for engine cooling system and heating system leaks. Service as required.
Possible Source(s):
- Loose drive belt
Action(s) to Take:
- Replace if cracked, missing or worn and/or adjust drive belt tension.
Possible Source(s):
- Water thermostat
Action(s) to Take:
- Check cooling system thermostat.
Possible Source(s):
- Plugged or partially plugged heater core
Action(s) to Take:
- Clean and backflush engine cooling system and heater core separately.
Possible Source(s):
- Reconnect and/or adjust to specifications.
- Vacuum hoses crossed or kinked
Action(s) to Take:
- Check to see if door vacuum control motors respond properly to movements of the function selector lever. Visually check vacuum hoses, and service as required.
Possible Source(s):
- Airflow control doors sticking or binding
Action(s) to Take:
- Check to see if doors and vacuum control motors respond properly to movements of function selector lever. If hesitation in movement is noticed, disconnect vacuum control motor arm or cable from door crank arm, and move crank arm by hand. Service sticking or binding door as required.
Possible Source(s):
- Vacuum control motor or hose leaks
Action(s) to Take:
- Disconnect multiple vacuum connector from control assembly selector valve and check each connector opening with hand operated vacuum pump. If one line leaks, test vacuum control motor by itself before replacing. Service vacuum hose(s) or replace vacuum control motor as required. Refer to the appropriate system vacuum leak tests.
Possible Source(s):
- Kinked, clogged, collapsed, soft, swollen, or decomposed engine cooling or heater system water hoses
Action(s) to Take:
- Replace damaged hoses and backflush engine cooling system, then backflush heater core separately, until all particles have been removed.
Possible Source(s):
- Blocked air inlet
Action(s) to Take:
- Check cowl air inlet for leaves and foreign material. Remove as required.
Airflow Changes Direction When Vehicle is Accelerated
Possible Source(s):
- Vacuum system leak
Action(s) to Take:
- Check vacuum system (including A/C vacuum check valve) with hand vacuum pump from control vacuum selector connector. Service tubing, or replace damaged components as required.
Air Comes Out of Windshield Defroster Hose Nozzle in Any Function Selector Lever Position
Possible Source(s):
- Vacuum system (this indicates a major leak, and is usually easy to locate)
Action(s) to Take:
- Listen for vacuum system leak. Look for disconnected vacuum hose connector. Use hand-operated vacuum pump, and check vacuum control motors for diaphragm leak. Also check for leaking A/C vacuum check valve, and leaking A/C vacuum reservoir tank and bracket. Service hoses or replace components as required. Refer to appropriate system vacuum leak tests.
Manual Air Conditioning A/C Blower Motor Does Not Operate (Any Speed)
Possible Source(s):
- Check fuse
Action(s) to Take:
- Check fuse 9 for continuity. If fuse is OK, check A/C blower motor.
Possible Source(s):
- A/C blower motor
Action(s) to Take:
- Run a 10 gauge or larger jumper wire directly from the B+ terminal to the positive lead (orange/black wire) of the A/C blower motor. Run a 10 gauge wire from frame ground to the negative lead (black) of the A/C blower motor. If the motor runs, check the electrical circuits for continuity.
Possible Source(s):
- Blower wire harness
Action(s) to Take:
- Check for proper installation of wire harness terminal connectors. Check wire-to-terminal continuity and continuity of wires in harness for open circuits. Service as required.
Possible Source(s):
- Heater blower motor switch
Action(s) to Take:
- Check heater blower motor switch for proper contact. Replace heater blower motor switch if required.
Possible Source(s):
- Function selector switch
Action(s) to Take:
- Check A/C damper door switch for proper contact. Replace if required.