The air distribution system utilizes a series of valves in order to control air flow though the ducts. There are 3 actuators in the series:

The various valves are hinged parts that open and close like doors in order to direct the airflow through different sections of the heater module. The valves provide the proper airflow for the selected operating mode.

In cases of vacuum line/harness leakage or hose collapse, it is not necessary to replace the entire vacuum harness. Repairs can be effected by cutting the hose and inserting a plastic connector.

All of the valves in the air distribution system are controlled by engine vacuum stored in the vacuum tank in the engine compartment. Vacuum is routed by a vacuum switch in the control assembly to 1 of the 3 spring-loaded, 3-position actuators.

The mode knob controls the vacuum switch. Changing the mode knob position causes the vacuum switch to direct engine vacuum to specific hoses and vent the remaining hoses. When a hose is vented to normal air pressure, the vacuum actuator's internal spring expands to hold the associated valve in one position. When vacuum is routed to the hose, the force of the vacuum overcomes the internal spring pressure and moves the valve to another position. In this way, the mode knob positions the valves for the selected operating mode.

The temperature valve regulates the amount of total airflow that passes through the heater core. The relative amounts of warm and cool air coming from the heater core determine the temperature of the air coming from the heater duct and the defroster nozzle.

Placing the temperature knob in the BLUE (cold) zone positions the temperature valve to stop all airflow through the heater core. With the valve in this position, only unheated air is sent to the heater duct and defroster nozzle.

Placing the temperature knob in the RED (hot) zone positions the temperature valve to divert all airflow through the heater core for maximum heating.

Hot coolant from the engine is directed through the heater core and returned to the cooling system when the engine is running. The heater core transfers heat from the coolant to the air passing through the core fins.

The heater system provides a choice of 3 basic operating modes. These are:

Additionally, the system gives the operator the option of combining the features of either the HTR and VENT, or the HTR and DEFROST operating modes, by selecting either of the BLEND positions.

A system of ducts and outlets directs air to the passenger compartment. In cases of poor air output, the ducts should be checked for obstructions such as leaves, dirt, or objects that may have fallen into the ducts from the passenger compartment.