Air Conditioning and Heating

CIRCUIT OPERATION
The air valves in the HVAC system, with the exception of the Temperature Valve, are moved by vacuum actuators. Vacuum is applied to the actuators through the Mode Selector in the Heater and A/C Control Assembly. The Mode Selector consists of a rotary vacuum which supplies vacuum to the vacuum actuators, according to the operating mode selected by the driver.

The Temperature Valve is moved by a small servo motor, which positions the door according to the voltage level from the Temperature Selector in the Heater and A/C Control Assembly. The Temperature Selector is a potentiometer position by the Temperature Control on the front panel.

A/C EVAPORATOR CORE
All air passing through the A/C Module moves across the A/C Evaporator Core. When the compressor is "ON," the core is cooled and removes moisture from the air.

OUTSIDE AIR VALVE
When the Mode Selector is moved to MAX, vacuum is applied to the Outside Air Vacuum Valve Actuator. The bellows are drawn in and the valve is moved to position "B." Air from inside the car is pulled into the A/C Module.

In any other position of the Mode Selector, no vacuum is applied and the vacuum actuator bellows are expanded. The Outside Air Valve is then in position "A." This opens the Outside Air Inlet and lets outside air into the A/C system.

A/C-HEAT VALVE
The A/C-Heat Valve Vacuum Actuator, which controls the A/C-Heat Valve, is bidirectional. The actuator is operated by two bellows and two vacuum switches. With the Mode Selector in "MAX," "NORM" and "VENT," vacuum is applied through the YELLOW hose, moving the A/C-Heat Mode Valve to position "A." Air flow is directed to the Instrument Panel Outlets with some air bleed to the Floor, Windshield and Side Window Outlets and no air flows from the Floor Outlets.

The A/C-Heat Valve Vacuum Actuator has vacuum applied to it through ORANGE hose with the Mode Selector in "OFF," "HTR," "BLEND" and "DEF." The valve is then moved to position "C" and all air is directed to the Floor, Windshield or Side Window Outlets depending on Mode Selector position. When the Mode Selector is in "B/L," neither bellows is under vacuum and the A/C-Heater Valve Vacuum Actuator moves to the Mid-Position. Air is then directed to the Instrument Panel Air Outlets and the Floor, Windshield or Side Window Outlets, depending on Mode Selector position

HEAT-DEFROST VALVE
The Heat-Defrost Valve Vacuum Actuator, which controls the Heat-Defrost Valve, is bi-directional. The actuator is operated by two vacuum motors and two vacuum switches. With the Mode Selector in "MAX," "NORM," "B/L," "VENT," or "HTR," vacuum is applied through the RED hose, moving the Heat-Defrost Valve to position "A." All airflow is directed to the Floor and Side Window Air Outlets with some air bleeding to the Windshield Air outlets.

The Heat-Defrost Valve Vacuum Actuator has vacuum applied through the WHITE hose with the Mode Selector in "DEF." The Heat-Defrost Valve is then moved to position "C" and all airflow is directed to the Windshield Air Outlets with some air bleeding to the Floor and side window outlets.

When the Mode Selector is in "OFF" and "BLEND," neither vacuum motors are under vacuum and the Heat-Defrost Valve Vacuum Actuator moves to position "B." Air is then directed to both the Floor, Side Window Air Outlets and the Windshield Air Outlets.

TEMPERATURE VALVE
With the Ignition Switch in "RUN," battery voltage is applied to the Temperature Valve Motor. This motor receives ground at all times. The Temperature Selector is a potentiometer with a wiper arm that is electrically tied to the Temperature Valve Motor Control input via CKT 362. When the Temperature Selector is moved between "C" and "H," voltage to the control input varies between battery voltage and zero volts. The Temperature Valve Motor solid state circuitry looks at the control input voltage and moves the motor to correspond to the control input voltage. The Temperature valve is moved to allow air to pass through and/or around the heater core, to achieve the desired passenger compartment temperature.