General Information
HEATER AND AIR CONDITIONERAll vehicles are equipped with a common heater-A/C housing assembly This system combines air conditioning, heating, and ventilating capabilities in a single unit housing mounted in the engine compartment, and a common air distribution duct system mounted under the instrument panel. On heater-only systems, the evaporator coil is omitted from the housing.
Outside outside air enters the vehicle through the cowl top opening at the base of the windshield, and passes through a plenum chamber to the right cowl side inlet. Air passes through the right cowl side inlet or the recirculation inlet in the right side of the dash panel into the recirculation housing in the engine compartment. A vacuum actuated recirculation air door controls whether outside air or air from the passenger compartment enters the heater-A/C system blower housing on the inboard side of the recirculation housing. Air flow velocity can then be adjusted with the blower motor speed selector switch on the heater-A/C control panel. The air intake openings must be kept free of snow, ice, leaves, and other obstructions for the heater-A/C system to receive a sufficient volume of outside air.
It is also important to keep the air intake openings clear of debris because leaf particles and other debris that is small enough to pass through the cowl plenum screen can accumulate within the heater-A/C housing. The closed, warm, damp and dark environment created within the heater-A/C housing is ideal for the growth of certain molds, mildews and other fungi. Any accumulation of decaying plant matter provides an additional food source for fungal spores, which enter the housing with the outside air. Excess debris, as well as objectionable odors created by decaying plant matter and growing fungi can be discharged into the passenger compartment during heater-A/C system operation.
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. The heater core, the evaporator coil, and the blend-air door are located in the heater-A/C housing. The heater-A/C housing is mounted to the dash panel in the engine compartment on top of the blower housing. A temperature control knob on the heater-A/C control panel determines the discharge air temperature by moving a potentiometer, which operates the electronic blend- air door actuator motor. This allows an almost immediate manual control of the output air temperature of the system.
The conditioned air is directed through an opening in the right side of the dash panel above the recirculation inlet into the distribution duct under the instrument panel. 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. Both mode control switches use engine vacuum to control the mode doors, which are operated by vacuum actuator motors.
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 a thermal expansion valve between the condenser and the evaporator coil to meter refrigerant flow to the evaporator coil. To maintain minimum evaporator temperature and prevent evaporator freezing, a fin sensing cycling clutch switch probe is inserted between the fins of the evaporator coil to cycle the compressor clutch as needed.