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

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

In cases of vacuum line/harness leakage or hose collapse, do not replace the entire vacuum harness. Repair the faulty component by cutting the hose and inserting a plastic connector.

All of the valves are controlled by engine vacuum. The engine vacuum is 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, three-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.

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