Heating and Defrosting (Without A/C)

FUNCTION CONTROL

System Air Flow Schematic:

The System Air Flow Schematic illustrates how 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 adds a vacuum schematic and chart to a basic airflow schematic.
^ It shows how the five lines in the air conditioner plenum vacuum harness are controlled by a selector valve assembly to operate three vacuum control motors.

The vacuum control motors control the movement of:
1. The heater and A/C air inlet duct door.
2. The heater air damper door.
3. The windshield defroster door.

The heater air damper door vacuum control motor has two vacuum lines.
^ When vacuum is applied to both lines, the heater air damper door moves to its full vacuum position.
^ When vacuum is applied to the blue line only, the heater air damper door moves to a partial vacuum position.
^ If vacuum is applied to the red line only (or neither line), the heater air damper door assumes a no-vacuum position.

Heater System Electrical Wiring Diagram:

The Heater System Electrical Wiring Diagram shows the system electrical wiring diagram.

TEMPERATURE CONTROL
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 an A/C electronic door actuator motor between the control assembly and the A/C air temperature control door

Control Assembly - Temperature Control Knob:

^ 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 control motors.
^ These vacuum control motors direct the airflow through the system.

The system uses a temperature blend method to provide controlled temperature to the vehicle interior,
^ All outside airflow from the blower passes through the A/C evaporator housing.
^ The temperature is regulated by heating a portion of the outside air and blending it with the remaining cooler outside air to the desired temperature.
^ Blending is varied by the A/C Air Temperature Control 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.

Depending upon the selection made with the function selector knob, the air is directed to:
^ The heater ducts.
^ The windshield defroster hose nozzle.
^ The instrument panel A/C registers.

SYSTEM AIRFLOW
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 A/C evaporator housing.
^ It is forced through and/or around the heater core, mixed, and discharged through outlets in the heater outlet floor duct to the floor area, or through the windshield defroster hose nozzles, as desired.
^ Several doors determine the volume of air that goes through the heater core and the particular outlet(s) through which it discharges.

The System Air Flow Schematic illustrates the airflow through the system with the various function selections available.

OFF
When the function selector knob is in the OFF position:
^ The heater and A/C air inlet duct door is at full vacuum. As a result, outside air is closed off and recirculate air is admitted to the system.
^ The windshield defroster door and the heater air damper door are both at full vacuum, closing off the passages to the defrosters.
^ The A/C air temperature control door position may be anywhere within the range of its cable travel from FULL HEAT to FULL COOL.
^ The A/C blower motor is OFF.

PANEL
When the function selector knob is in the PANEL position:
^ The heater and A/C air inlet duct 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 A/C registers.
^ The heater air damper door is at no vacuum to block airflow to the floor registers, and the windshield defroster door is at full vacuum, closing off airflow to the defrosters.
^ The temperature selector may be adjusted to heat the air, if desired.
^ The A/C blower motor is ON.

FLOOR
When the function selector knob is in the FLOOR position:
^ The heater and A/C air inlet duct door is in the no vacuum position to block recirculate air and admit outside air.
^ The heater air damper door is in the vacuum position which closes off all but a minimum of airflow to the defroster.
^ The A/C air temperature control door position will channel airflow so that a desired temperature level will be achieved.
^ The windshield defroster door is in the no vacuum position to block air circulation to the panel registers.
^ The A/C blower motor is ON.

MIX
When the function selector knob is in the MIX position:
^ The heater and A/C air inlet duct door and the windshield defroster door are in the no vacuum position.
^ The heater air damper door is in the partial vacuum position.
^ The A/C blower motor is ON.

DEFROST
When the function selector knob is in the DEFROST position:
^ The heater and A/C air inlet duct door is in the no vacuum position to admit outside air.
^ Both the heater air damper door and the windshield defroster doors are in the no vacuum position so that most of the incoming air is directed to the windshield defroster hose 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 A/C blower motor is ON.