Control Assembly, HVAC

CLIMATE CONTROL ASSEMBLY
The heater is a blend air type which receives its outside air supply from the cowl inlet. The heater control is located in the instrument panel to the right of the steering column. It includes the function selector knob, temperature control knob and the heater blower motor switch.

Airflow Control
Blended, heated, and unheated outside air is directed to the instrument panel registers, the floor outlets and A/C side window demister and hoses, or the defroster outlets by the vent-heat door and the heat-defrost door. The function knob controls the doors by means of a vacuum selector and A/C plenum vacuum harness between the control assembly and plenum. The function knob also controls the outside air door by means of a vacuum control motor.

When the function control knob is at the VENT position, the vent-heat door is positioned to allow air to come out of the instrument panel registers.

When the function control knob is at the HEAT position, the vent-heat door closes to the instrument panel registers and airflow is directed to the floor and A/C side window demister and hoses with a small amount of bleed to the defroster. In the MIX position, airflow is divided between floor demisters and defroster. In the DEFROST position, airflow is directed through the windshield defroster hose nozzle with a small amount of bleed to the floor and side window demisters.

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 with unheated air. It is controlled by the temperature control knob of the heater control located in the instrument panel.

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 in the heater plenum chamber case for distribution.

Blower Motor Control
The blower motor is controlled by a four-position heater blower motor switch. 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 four of the operating positions and 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 (next position), current flow in the ground circuit is through two heater blower motor switch resistor coils to obtain a medium low operating speed.

With the heater blower motor switch at MEDIUM HIGH (position next to HI), 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 blower operating speed.

The heater blower motor switch has no OFF position. The functional control must be at the OFF position to turn off blower motor.