Controls

Control Panel
The control assembly in the instrument panel contains three controls: a switch to control blower speed, one rotary knob to select the desired operating mode, and a second rotary knob to control heated air temperature.

The controls are illuminated when the headlamps or running lights are on Electrical voltage is provided through the instrument panel lighting circuit. The control assembly lamp is in parallel with the instrument cluster bulbs, the radio dial bulb and certain other interior illumination bulbs. Brightness of the dial illumination is controlled by the dimmer control of the headlamp switch.

Temperature Control
On all S/T models, the temperature door is controlled by an electric motor that positions the door based on the temperature knob location.

When the temperature control is in the "Blue" (Cold) position, air delivered by the heater system is unheated. When the temperature control is in the "Red" (Hot) position, all air passing through the heater module is heated before it is discharged. Intermediate positions of the temperature control result in a mixture 0 heated and unheated air to provide more moderate air temperatures.

As the temperature control rotates away from the "Blue" (Cold) position, the temperature valve moves away from the heater core to allow some air to flow through the heater core. The closer the temperature control is moved toward the "Red" (Hot) position, the more the temperature valve turns away from the entrance to the heater core and The greater The airflow 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 and causes all of the airflow to go through the heater core for maximum heating. This method of temperature control provides a very rapid response to any change in temperature selection throughout the entire range when the engine is warmed up.

Mode Control
The mode control knob operates a rotary vacuum switch that routes engine vacuum to specific hoses in the vacuum harness. These hoses control vacuum actuators on the defroster duct. Each actuator operates an air valve (a door-like hinged deflector) that routes airflow to the various outlets of the heater/defrost system.

Although, the control knob positions are shown as symbols on the face plate, the direction of air flow remains the same, they are; "OFF," "VENT," "BI-LEV," "HTR," "BLEND," and "DEFROST."
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 from a fuse in the fuse block when the ignition is "ON." In the various blower speed positions, the circuit continues through the heater wiring harness to the resistor assembly near the blower motor.
From the resistor assembly, the circuit goes to the blower motor terminal to operate the blower motor. The blower motor circuit is completed to ground by a wire in the heater wiring harness that goes from the blower motor terminal to a terminal at the cowl panel sheet metal near the blower assembly in the engine compartment.