Operation
OPERATION
The standard front heating-A/C system is a blend-air type system. In a blend-air system, a blend-air door controls the amount of conditioned air that is allowed to flow through, or around, the heater core. The temperature control determines the discharge air temperature by moving the blend-air door. This design allows almost immediate control of output air temperature.
FRONT SYSTEM
The standard front heating-A/C system pulls outside (ambient) air through the fresh air intake (4) located at the cowl panel at the base of the windshield and into the air inlet housing above the heating, ventilation and air conditioning (HVAC) housing and then passes through the A/C evaporator (7). Air flow is then directed either through or around the heater core (2). This is done by adjusting the position of the blend-air door (3) with the temperature control located on the A/C-heater control in the instrument panel. Air flow is then directed out the floor outlet (8), instrument panel outlet (10) or the defroster outlet (1) in various combinations by adjusting the position of the mode-air doors (9 and 11) using the mode control located on the A/C-heater control. The temperature and mode control use electrical actuators to operate the air doors when equipped with the automatic temperature control (ATC) system and cables when equipped with the manual temperature control (MTC) system.
The velocity of the air flow out of the outlets can be adjusted with the blower speed control located on the A/C-heater control.
On models equipped with A/C, the fresh air intake can be shut off by pressing the Recirculation button on the A/C-heater control. This will operate the electrically actuated recirculation-air door (5), which closes off the fresh air intake. With the fresh air intake closed, the conditioned air within the vehicle is pulled back into the HVAC housing through the recirculation air intake (6) located within the passenger compartment.
The A/C compressor can be operated by pressing the A/C (snowflake) button on the A/C-heater control. It will automatically operate when the mode control is set in any Mix to Defrost position. This will remove heat and humidity from the air before it is directed through or around the heater core. The mode control on the A/C-heater control is used to direct the conditioned air to the selected system outlets.
The defroster outlets receive airflow from the HVAC housing through the molded plastic defroster ducts, which connect to the HVAC housing defroster outlet. The airflow from the defroster outlets is directed by fixed vanes in the outlet grilles and cannot be adjusted.
The side window demister outlets receive airflow from the HVAC housing through the molded plastic demister ducts. The demisters direct air from the HVAC housing through the outlets located on the top corners of the instrument panel. The airflow from the side window demister outlets is directed by fixed vanes in the demister outlet grilles and cannot be adjusted. The demisters operate when the mode control is positioned in the bi-level, floor, floor-defrost and defrost settings.
The instrument panel outlets receive airflow from the HVAC housing through molded plastic instrument panel ducts. The two end panel ducts direct airflow to the left and right instrument panel outlets, while the center panel duct directs airflow to the four center panel outlets. Each of these outlets can be individually adjusted to direct the flow of air.
The floor outlets receive airflow from the HVAC housing through the floor distribution ducts. The front floor outlets are integral to the molded plastic floor distribution duct, which is secured to the bottom of the HVAC housing. The plastic rear floor distribution duct attaches to the floor distribution duct and provides conditioned air to the intermediate seating positions.
NOTE: It is important to keep the air intake opening clear of debris. Leaf particles and other debris that is small enough to pass through the cowl opening screen can accumulate within the HVAC housing. The closed, warm, damp and dark environment created within the 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 fresh intake-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 operation if the air intake opening is not kept clear of debris.
The standard front A/C system is designed for non-CFC, R-134a refrigerant and uses an A/C expansion valve (TXV) to meter the flow of refrigerant to the A/C evaporator. The powertrain control module (PCM) or engine control module (ECM) (depending on engine application) adjusts the angle of the compressor swashplate as necessary to optimize A/C system performance and to protect the A/C system from evaporator freezing.
REAR SYSTEM
The available rear A/C system pulls interior air through the air intake grille into the rear evaporator trim panel and into the rear blower motor in the rear evaporator housing, then through the rear A/C evaporator. Air flow velocity can be adjusted with the blower speed control located on the rear A/C-heater control.
The rear ceiling air outlets receive airflow from the rear evaporator housing through the molded plastic ceiling ducts. Airflow direction from the air outlets can be adjusted individually and the air outlets can be serviced separately.
The rear A/C system is designed for use of non-CFC, R-134a refrigerant and uses an "H" valve-type thermal expansion valve (TXV) to meter the flow of refrigerant to the rear A/C evaporator. An evaporator temperature sensor is used to maintain minimum evaporator temperature and prevent evaporator freezing.