General Information

After the heated and unheated air flows are mixed beyond the heater core, the combined airflow comes to the mode valves. These valves work in combination to control airflow through the passage that feeds the instrument panel outlets. For the VENT mode, the vacuum is directed to the vacuum actuators and the mode valve(s) open to allow air to flow to the instrument panel outlet, as shown by the symbol. In the HTR, and DEFROST modes, the vacuum actuators are vented and the mode valve(s) close to prevent airflow to the instrument panel outlets, as shown by the symbol.

When the BI-LEV mode is selected, only the lower mode valve is opened. This divides the airflow so the instrument panel outlets, the floor air outlet(s), the defroster nozzles and the side window defogger outlets all receive a share of the air, as shown by the symbol.

Another vacuum controlled mode valve in the air distribution system is the defroster valve. In the HTR and BI-LEV modes, vacuum is applied to the defroster valve actuator. This moves the defroster valve to divert almost all of the airflow to the floor air outlet(s) to heat the passenger compartment. Only a slight amount passes through an opening in the defroster valve and goes to the windshield defroster nozzle, as shown by the symbol.

In the DEFROST mode, the defroster valve actuator is vented to normal air pressure and the spring in the actuator holds the defroster valve in a position to route most of the airflow to the windshield defroster passage in the air distributor, as shown by the symbol. In the VENT mode, the defroster valve also is held in this position. Only a slight amount of the total airflow passes through the opening in the defroster valve and goes to the air outlet(s), as shown by the symbol.