Air Distribution System

Air enters the heater module where it is heated as necessary before being sent to the proper outlets for discharge into the passenger compartment. Within the heater module, valves ("doors") guide the airflow in response to the positions of the temperature control knob and the mode control knob in the control.


Vacuum System






All valves in the heater module except the temperature valve are controlled by engine vacuum drawn from the vacuum tank in the engine compartment. The vacuum is routed by a vacuum selector valve in the control to spring-loaded vacuum actuators on the heater module. Vacuum stored in the vacuum tank is prevented from bleeding back to its source during conditions of low engine manifold vacuum (acceleration, hard pulling, etc.) by a check valve in the vacuum line.

The vacuum selector valve in the control is controlled by the mode control knob. For each mode control knob position, the vacuum selector valve directs vacuum to specific hoses to overcome the force of the spring within the appropriate vacuum actuators. The vacuum selector valve also vents (to normal air pressure) the hoses to each remaining vacuum actuator. allowing the actuator's spring to expand. This results in the valves being properly positioned for the selected operating mode.

The bi-level and vent valves have two-position vacuum actuators. When vacuum is directed to either actuators vacuum chamber, the vacuum pulls in a flexible diaphragm that forms one wall of the chamber. This draws a movable shaft attached to the diaphragm. The shaft is linked to the corresponding valve, and it operates the valve when vacuum is applied.

When the vacuum chamber is vented to normal air pressure, an external spring moves the shaft back to its original position. The shaft, in turn, returns the valve to its original position.

The defroster/heater valve has a three-position mode valve actuator with two vacuum hoses and two vacuum chambers, one at each end of the actuator. In effect, the three-position mode valve actuator acts like a pair of two-position actuators placed end-to-end. When vacuum is directed to either chamber, that chamber's diaphragm moves the mode valve operating linkage from its centered position to one extreme of travel. Venting that chamber while directing vacuum to the opposite chamber causes the linkage to move to its opposite extreme. Venting both chambers allows external torsion springs to center the linkage. The center position of the defroster/heater valve creates the blend mode.

Temperature Valve and Heater Core

Module Airflow:

The temperature of the air discharged from the heater system is regulated by controlling the relative amounts of warm and cool air that are mixed together downstream from the heater core area. The part of the total airflow that is allowed to pass through the heater core (14) is governed by the position of the temperature valve (16).
Hot coolant from the engine's cooling system is directed through the heater core (14). The heater core (14) transfers heat from the coolant to the air passing through the heater core fins.

Mode Valve Housing

After the heated and unheated airflows are mixed, the combined airflow comes to the mode valve housing. In vent mode, the vent mode valve actuator is engaged as well as the bi-level mode valve actuator. This directs all the air to the instrument panel outlets.
in bi-level mode, the vent mode valve remains closed (allowing air to the defroster/heater door), while the bi-level mode valve opens, allowing air to the instrument panel outlets. The defroster/heater door directs air to the floor air outlets. A small amount of air goes to the side window defrost outlets.

In heater mode, both the vent and bi-level doors remain closed and the defroster/heater door moves up, directing most of the air to the floor air outlets.

In blend mode, both chambers of the heater/defrost actuator are vented and the heater/defrost valve moves to a mid-position allowing air up to the defroster and down to the heater outlet. Both the vent and bi-level doors remain closed.

In defrost mode, the heater/defrost valve moves down and forces the air up to the defroster outlet. A small amount of air still flows to the heater outlet because of a fixed bleed.

Air Outlets






There are adjustable high-level air outlets in the instrument panel. In addition, there are two side window defrost outlets, one at each end of the instrument panel. All outlets are fed by the air distributor.

Ventilation






The air distribution system provides fresh air ventilation for the passenger compartment in all operating modes. Even in the "OFF" mode, fresh outside air is forced into the air distribution system by the forward movement of the vehicle.

After being warmed to the desired temperature, the air is discharged from the outlets. When all windows are closed, the addition of outside air builds a slight positive pressure within the passenger compartment. The pressure forces stale air to leave the vehicle through a pressure relief valve near the left side quarter panel in front of the rear fascia.