The control assembly in the instrument panel contains the following three controls:
- A switch to control blower speed
- A rotary knob to select the desired operating mode
- A second rotary knob to control the air temperature
The controls are lit when the headlamps are ON. The instrument panel lighting circuit provides voltage. The control assembly lamp is in parallel with the following components:
| • | The instrument cluster bulbs |
| • | The radio dial bulb |
| • | Other interior illumination bulbs |
The dimmer control of the headlamp switch controls the brightness of the dial illumination.
Temperature Control
The temperature valve is controlled by an electric motor. The motor positions the valve based on the temperature knob location.
When the temperature knob is in the Blue (Cold) position, the air that is delivered by the heating system is unheated. When the temperature control is in the Red (Hot) position, all of the air that passes though the heater is heated before the air is discharged. Intermediate positions of the temperature control result in a mixture of heated and unheated air in order to provide more moderate air temperatures.
As the temperature control is moved away from the Blue (Cold) position, the temperature valve moves away from the heater core. This allows some air to flow through the heater core. As the temperature control is moved farther toward the Red (Hot) position, the following actions occur:
- The temperature valve is turned farther away from the entrance to the heater core
- The airflow increases through the heater core
Heating a greater portion of the total airflow in this manner results in a warmer discharge of air from the outlets.
When the temperature control is in the full Red (Hot) position, the temperature valve blocks off the passage that allows air to bypass the heater core. This causes all of the airflow to go through the heater core for maximum heating. This method of temperature control provides a rapid response to any change in temperature selection throughout the entire range when the engine is warmed up.
Mode Control
The mode rotary control knob operates a rotary vacuum switch that rotates engine vacuum to specific hoses in the vacuum harness. These hoses control various vacuum actuators on the HVAC system. Each actuator operates an air valve (a door-like hinged deflector) that routes the air to the various outlets as indicated by the symbols on the face plate.
For additional information on mode operation, refer to Operating Modes.
Blower Speed Control
The blower switch provides a choice of various blower speeds. The blower switch receives power through a fuse in the fuse block when the power is ON. In the various speed positions, the circuit continues through the heater wiring harness to the blower motor resistor assembly near the blower motor.
The circuit goes from the resistor assembly to the blower motor terminal in order to operate the blower motor.
The blower motor relay provides battery voltage to the blower motor assembly only during high blower motor assembly speed. The blower motor circuit is completed to ground by a wire in the heater wiring harness. The wire goes from the blower motor terminal to a terminal at the dash sheet metal near the blower assembly in the engine compartment.
