Heater and Defroster Operation

Heater And Defroster Operation

The heater is part of the engine cooling system and depends on normal engine operating temperature and airflow through the cowl fresh air intake to heat the interior of the vehicle. During heater operation, close the fresh air vents.


The Off, Heat and Defrost buttons on the heater control panel operate a vacuum control switch which controls two vacuum motors.
- When the Off button is pressed, the vacuum switch shuts off vacuum to the air inlet door vacuum motor. A spring closes this door, preventing any outside air from entering the heater.
- When the Heat button is pressed, the air inlet door is opened by the air inlet vacuum motor and air will flow through the heat transition housing and out of the floor heat distributor.
- When the Defrost button is pressed, the vacuum switch directs vacuum to the defrost vacuum motor, which closes the door to the floor heat distributor. Airflow is then directed through the defroster hoses onto the windshield. The air inlet door remains open to allow airflQw through the heat transition housing.

The temperature control lever operates the blend air door in the heater core housing.
- At the full right position, all air is directed through the heater core providing maximum heat flow.
- At the full left position, all air is directed around the heater core providing unheated fresh air.
- The temperature control lever may be placed in any in-between position to provide a blend of cool, fresh, outside air and heater air.
However, either the Heat or Defrost button must be pressed before any air can enter the vehicle.

If additional airflow is required, the blower motor should be operated at one of the three available speeds.