Heater Control Valve: Description and Operation

TEMPERATURE CONTROL SYSTEM
A rotary dial on the control panel regulates both the air mix door and the flow of engine coolant to the heater core.
OPERATION
Through a gear reduction and cam/lever mechanism, rotating the dial moves the heat control cable. Through a dial linkage at the heater core, the cable moves the air mix door and a vacuum control valve. The control valve, in turn, regulates vacuum to a diaphragm-controlled engine coolant valve. Rotating the dial from "MAX COOL" toward "HOT" sends a proportionate amount of heated engine coolant to the heater core and air through the core, to heat the car.