System Airflow

SYSTEM AIRFLOW
The system pulls outside (ambient) air through the cowl opening at the base of the windshield. Then it goes into the plenum chamber above the heater-A/C housing. On air conditioned vehicles, the air passes through the evaporator. Air flow can be directed either through or around the heater core. This is done by adjusting the blend-air door with the TEMP control on the instrument panel. The air flow can then be directed from the panel, floor and defrost outlets in various combinations using the mode selector. There are 17 different mode selections possible. Air flow velocity can be adjusted with the blower speed selector switch on the instrument panel.

On A/C equipped vehicles the ambient air intake can be controlled by opening and closing the recirculating air door. When placed in RECIRC, air that is inside vehicle is removed continuously and recirculated through unit housing. Ambient air cannot be controlled on vehicles without A/C. The system uses outside air at all times.

The air conditioning compressor can be engaged by turning the fan switch counterclockwise from the off position. It can also be engaged by placing the mode control in the mix to defrost positions. This will remove heat and humidity from the air before it is directed through or around the heater core.

The heater and optional air conditioner are blend-air type Systems. In a blend-air system, a blend-air door controls the amount of unconditioned air (or cooled air from the evaporator on models with air conditioning) that is allowed to flow through, or around, the heater core. A temperature control knob on the heater-A/C control panel determines the discharge air temperature by moving a cable, which operates the blend-air door. This allows an almost immediate manual control of the output air temperature of the system.

The mode control knob on the heater-only or heater-A/C control panel is used to direct the conditioned air to the selected system outlets. The mode control switch uses a cable to control the mode door, while the recirculation air door is operated by a vacuum actuator motor.

On air conditioned vehicles, the outside air intake can be shut off by selecting the recirculation mode (Recirc) with the mode control knob. This will operate a vacuum actuated recirculating air door that closes off the outside fresh air intake and recirculates the air that is already inside the vehicle.

The optional air conditioner for all models is designed for the use of non-CFC, R-134a refrigerant. The air conditioning system has an evaporator to cool and dehumidify the incoming air prior to blending it with the heated air This air conditioning system uses an evaporator probe to maintain minimum evaporator temperature and prevent evaporator freezing, and cycles the compressor clutch.