With A/C

A heater valve is used to control the flow of engine coolant to the heat exchanger. The heater valve is vacuum operated. A separate vacuum switch is located in the ventilation control assembly to operate the heater valve.

The valve is normally open and allows engine coolant to flow through the heat exchanger.

The interior temperature is then controlled by regulating the amount of air which passes through the heat exchanger. However, when the temperature control lever is moved almost fully to the left (no heating desired) the switch will open and supply vacuum. This will close the heater valve.