| Symptom | Possible Cause |
|---|---|
| Insufficient, Erratic, or No Heat or Defrost | Low radiator coolant. Engine overheating. Loose fan belt. Faulty thermostat. Heater core plugged. Loose or misaligned cables. Vacuum hoses collapsed, kinked or crossed. Air flow control doors sticking or binding. Vacuum motor or hose leaks. Defective or kinked water hoses. Blocked air inlet. Vent open. |
| Too Much Heat | Loose or misadjusted cables. Temperature control door stuck fully open. ATC servo improperly adjusted. |
| Air Flow Changes Direction When Vehicle is Accelerated | Vacuum system leak.Cowl Vent System Leaks Air. Vent door not fully closed. Vent door seal damaged. |
| Cowl Vent System Leaks Air | Vent door not fully closed. Vent door seal damaged. |
| Blower Does Not Operate Properly | Blower motor defective. Blower resistor defective. Blower wire harness defective. Blower switch defective. Selector valve switch defective. |
| Blower Motor Inoperative | Blown fuse. Open circuit. Overheated thermal limiter. Defective blower motor. Defective blower switch. |
| Air Comes Out Of Defroster Outlet In Any Mode Selector Lever Position | Vacuum system leak. |
CONDITION AND POSSIBLE CAUSE
HISSING VACUUM SYSTEM OR MODE SELECTOR VALVE
- Check in-line and control assembly multiple connectors for proper installation. Listen for hiss. If hiss stops, re-check system operation. If hiss continues, move mode lever to determine what mode valve positions are leaking. If all positions leak, proceed to step 2. If some but not all leak, proceed to step 3.
- Check vacuum source tube (Black) from reservoir to control assembly for cuts or disconnection and reconnect or repair if necessary. Listen for hiss. If hiss stops, re-check system operation. If hiss continues, go to step 4.
- Determine what color tubes are used in leaking mode selector valve positions. Pinch off suspect tubes, one at a time, near respective vacuum motor. Listen for hiss. If hiss continues, go to step 5. If hiss stops, check tube connection to vacuum motor and repair and/or reconnect if loose or split. Listen for hiss. If hiss continues replace vacuum motor. Re-check operation.
- Pinch off source tube (Black) at control assembly. Listen for hiss. If hiss stops, replace selector valve. Re-check system operation. If hiss continues, re-check source tube, connections, reservoir and check valve. Service and repair as necessary.
- Pinch off suspected tubes, one at a time, near control assembly and/or in-line connector. Listen for hiss. If hiss continues, replace mode selector valve. If hiss stops, check tube for cuts or damage. Service and repair as required. Re-check system operation.