Air Distribution System

Control of airflow through the HVAC module is regulated by vacuum-actuated doors. At various positions of the knobs on the control assembly, mode doors mix and direct cooled, heated, and outside air through the air ducts.

In case of vacuum line/harness leakage or hose collapse, it is not necessary to replace the entire vacuum harness assembly. Replacement can be made by cutting the hose and inserting a plastic connector. If an entire hose must be replaced, cut the hose off at the connector and then attach new hose directly to the vacuum solenoid control assembly.

Vacuum System

All valves except the temperature valve are controlled by checked engine vacuum stored in the vacuum tank in the engine compartment. Vacuum is routed by a vacuum switch in the control assembly to either of the spring-loaded three-position vacuum actuators. One vacuum actuator is linked to each valve.

The mode knob controls the vacuum switch. For each mode knob position, the vacuum switch will direct engine vacuum to specific hoses and vent the remaining hoses. When a hose is vented to normal air pressure, the vacuum actuators internal spring will expand and 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.

Ducts and Outlets

A system of ducts and outlets directs air to the passenger compartment. In cases of poor air output, defroster, heater, air conditioning, and vent ducts should be checked for obstructions.