The vacuum actuators move the air valves in the HVAC system (except the temperature valve). 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. The rotary vacuum switch supplies vacuum to the vacuum actuators according to the operating mode selected by the driver. A small servo motor moves the air temperature actuator. The small servo motor 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
When the ignition switch is in the RUN position, battery voltage is applied to the air temperature actuator. The actuator receives ground at all times through the following components:
| • | CKT 251 |
| • | Ground G204 |
The temperature selector is a potentiometer with a wiper arm. The wiper arm is electrically tied to the air temperature input through CKT 733.
When the temperature selector is moved between COLD and HOT, voltage to the control input varies between 1 and 12 volts. The temperature valve motor solid state circuitry performs the following tasks:
| • | Looks at the control input voltage |
| • | Moves the motor to correspond to the control input voltage |
The temperature valve moves for the following reasons:
| • | In order to allow the air to pass through the heater core |
| • | In order to allow the air to pass around the heater core |
This control achieves the desired passenger compartment temperature.
