Air Door: Description and Operation
TEMPERATURE BLEND DOORThe 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 center of 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 and it remains unheated. 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.