The following air valves are used in the distribution system:

Within the heater module is a series of air valves. These air valves are hinged parts that act like doors. The air valves direct the airflow through the various sections of the heater module in order to provide the proper airflow for the selected operating mode. A control cable from the heater control assembly actuates each air valve.

Controlling the relative amounts of warm air and cool air coming from the heater module regulates the temperature of the air coming from the air distribution duct. The temperature valve governs the part of the total airflow through the heater module that passes through the heater core. A control cable, working through a lever on the temperature valve shaft, operates the temperature valve. The valve defaults to full cold with no cable attached.

When the temperature rotary knob in the control assembly is in the full COLD position, the position of the temperature valve stops all of the airflow through the heater core, so that only unheated air passes to the air distribution duct.

As the temperature rotary knob moves away from the full COLD position, the temperature control cable opens the temperature valve in order to allow the passage of an increasing amount of air through the heater core. At the same time, the temperature valve reduces the amount of unheated air that enters the mixture. The result is a very responsive control of the air temperature discharged through the heater ducts and the defroster.

When the temperature rotary knob reaches the full HOT position, the temperature control cable holds the temperature valve in a position that diverts all of the airflow through the heater core for the maximum heater.

The hot coolant from the engine is directed through the heater core. When the engine is running the hot coolant returns to the cooling system.

The heater system provides a choice of three basic operating modes: