Auxiliary Heater Vacuum System

The auxiliary heater control switch in the instrument panel has four positions: OFF, LO, MED and HI. In any switch position except OFF, the auxiliary heater control switch routes battery voltage to the auxiliary heater blower motor when the ignition switch is in RUN, as explained in "Auxiliary Heater".

In addition, the switch routes vacuum from the vacuum tank to the vacuum actuator that opens the auxiliary heater hot water valve. When open, the hot water valve admits heated coolant to the auxiliary heater inlet pipe and auxiliary heater core.

When the auxiliary heater control switch is turned OFF, electric voltage to the blower motor is cut off and the hot water valve vacuum actuator is vented to atmospheric air to close the valve. This stops the flow of coolant to prevent unwanted heat.