Heating and Defrosting (Without A/C)

AIRFLOW

System Airflow Schematic:

The heater assembly is a blend air system, receiving outside air through the blower inlet, which is connected directly to an opening in the upper cowl. Outside air is drawn into the system from the cowl, through the blower inlet into the blower housing. It is forced through and/or around the heater core, mixed, and then discharged through outlets in the discharge air duct to the floor area or through the defroster outlets, depending upon the type of climate control desired. Several doors determine the amount of air that goes through the heater core and the particular outlet(s) through which it discharges. The following illustration shows the airflow through the system with the various function selections available.

OFF
When the function selector knob is in the OFF position:
^ The outside-recirculate door is at full vacuum. As a result, the outside air is closed off and recirculate air is admitted to the system.
^ The panel-defrost door and the floor-panel door are both at full vacuum, closing off the passages to the defrosters.
^ The blend door position may be anywhere within the range of its cable travel from FULL HEAT to FULL COLD.
^ The blower motor is OFF.

PANEL
When the function selector knob is in the PANEL position:
^ The outside-recirculate door, with no vacuum being applied, will block recirculate air and admit outside air. From there, airflow is directed through the system to the instrument panel registers.
^ The floor-panel door is at no vacuum to block airflow to the floor registers, and the panel-defrost door is at full vacuum, closing off airflow to the defrosters.
^ The temperature selector may be adjusted to heat the air, if desired.
^ The blower motor is ON.

FLOOR
When the function selector knob is in the FLOOR position:
^ The outside-recirculate door is in the no vacuum position to block the recirculate air and admit the outside air.
^ The floor-panel door is in the vacuum position which closes off all but a minimum of airflow to the defroster.
^ The blend air door position will channel airflow so that a desired temperature level will be achieved.
^ The panel-defrost door is in the no vacuum position to block air circulation to the panel registers.
^ The blower motor is ON.

MIX
When the function selector knob is in the MIX position:
^ The outside-recirculate air door and the panel-defrost door are in the no vacuum position.
^ The floor-panel door is in the partial vacuum position.
^ The blower motor is ON.

DEFROST
When the function selector knob is in the DEFROST position:
^ The outside-recirculate air door is in the no vacuum position to admit outside air.
^ Both the floor-panel and the panel-defrost doors are in the no vacuum position so that most of the incoming air is directed to the defroster nozzles. There is a slight air bleed to the floor registers.
^ The temperature control knob setting will determine the amount of heat being introduced into the airflow.
^ The blower motor is ON.

TEMPERATURE CONTROL

Control Assembly - Temperature Control Knob:

Temperature control of the heater and power ventilation system is determined by the position of the temperature control knob (between COOL and WARM) of the control assembly, and is accomplished by means of a blend door actuator between the control assembly and the temperature blend door. System airflow is manually controlled by the control assembly. A vacuum selector valve, controlled by the function control knob, distributes vacuum to the various door vacuum motors which in turn, direct the airflow through the system.

The system uses a temperature blend method to provide controlled temperature to the vehicle interior. With this method, all outside airflow from the blower passes through the heater case to the plenum assembly. Temperature is then regulated by heating a portion of the outside air and blending it with the remaining cooler outside air to the desired temperature. Temperature blending is varied by the temperature blend door which controls the amount of air that flows through or around the heater core, where it is mixed and directed into the distribution plenum The air is finally directed to the heater ducts, the defroster nozzles, or the instrument panel registers, depending upon the selection made with the function selector knob.

SYSTEM AIRFLOW AND VACUUM CONTROLS
The System Airflow Schematic shows how the air is circulated through the system when the function selector knob is in each of its detent positions.

Heater System Vacuum Schematic And Selector Test Chart:

The Heater System Vacuum Schematic And Selector Test Chart shows how the five lines in the vacuum harness are controlled by a selector valve assembly to operate three vacuum motors. The motors control the movement of:
^ The outside-recirculate door.
^ The panel-floor door.
^ The panel-defrost door.
The panel-floor door vacuum motor has two vacuum lines. When vacuum is applied to both lines, the door moves to its full vacuum position. When vacuum is applied to the blue line only, the door moves to a partial vacuum position. If it is applied to the red line only (or neither line) the door will assume a no vacuum position.