Temperature Controls - HVAC System - Manual - Electronic Controls

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 A/C Control Assembly. The Mode Selector consists of a rotary vacuum switch that supplies vacuum to the vacuum actuators according to the operating mode selected by the driver. The Air Temperature Actuator is moved by a small servo motor which positions the door according to the voltage level from the Temperature Selector in the Heater A/C Control assembly. The Temperature Selector is a potentiometer positioned by the Temperature Control Knob on the front of the Heater A/C Control Assembly.

Air Temperature Actuator
With the Ignition Switch in RUN, battery voltage is applied to the Air Temperature Actuator. The actuator receives ground at all times through circuit 251 and ground G204. The Temperature Selector is a potentiometer with a wiper arm that is electrically tied to the Air Temperature Actuator input via circuit 733. When the Temperature Selector is moved between COLD and HOT, voltage to the control input varies between one and twelve 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.