Control Assembly, HVAC

HEATER CONTROL ASSEMBLY
The illustration shows the heater control.

The heater control is installed in a rectangular cutout in the lower center area of the instrument panel. It contains three rotary switches. The extreme left switch is the heater blower motor switch.

Airflow Control
The function selector knob is located on the extreme right of the heater control. The knob rotates to positions: PANEL, OFF, PNL/FLR, FLOOR, FLR/DEF and DEFROST. In the OFF position, the recirculation door is closed to stop outside air from passing through the climate control system and to keep the in-vehicle air circulating. To shut off the blower motor, the function selector knob must be turned to the OFF position.

Temperature Control
The temperature blend door, located in the heater air plenum chamber, directs outside air to flow through the heater core for heating, or to bypass the heater core for ventilation. It is controlled by the temperature control knob of the heater control.

A heater temperature cable connects the temperature control knob to a cam which operates the temperature blend door. When the temperature control knob is at the COOL position, the temperature blend door directs outside air to bypass the heater core. When the temperature control knob is at WARM, the temperature blend door directs outside air through the heater core where the air is heated.

Positioning the temperature control knob in any position between COOL and WARM causes the temperature blend door to direct more or less outside air through or around the heater core for whatever proportion of heated or unheated outside air is desired.

The air blends together as it leaves the heater core into the heater air plenum chamber for distribution.

Blower Motor Control
The blower motor is controlled by a four-position heater blower motor switch located on the left side of the heater control. The four positions are LOW, MEDIUM LOW, MEDIUM HIGH and HIGH. The four operating speeds are obtained with a heater blower motor switch resistor connected in series with the heater blower motor switch operating on the ground side of the blower motor.

With the heater blower motor switch at LOW, current flow in the ground circuit is through three heater blower motor switch resistor coils to obtain the lowest operating speed.

With the heater blower motor switch at MEDIUM LOW, current flow in the ground circuit is through two heater blower motor switch resistor coils to obtain a medium low motor operating speed.

With the heater blower motor switch at MEDIUM HIGH, current flow in the ground circuit is through one heater blower motor switch resistor coil to obtain a medium high operating speed.

With the heater blower motor switch at HIGH, current flow in the ground circuit bypasses the heater blower motor switch resistor to obtain the maximum operating speed.