The standard front and available rear heating-A/C systems used in this vehicle are blend-air type systems. 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. In the available front dual zone system, separate blend-air doors are used to provide completely independent side-to-side temperature control of the discharge air. The temperature control(s) determines the discharge air temperature(s) by operating the blend door actuator(s), which move the blend-air door(s). This design allows almost immediate control of output air temperature(s).

FRONT SYSTEM

Fig. 3: Blend Air System Schematic

NOTE: Typical blend-air type HVAC system shown.

The 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 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(s) (3) with the temperature control(s) 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 operated the air doors.

The velocity of the air flow out of the outlets can be adjusted with the blower speed control located on the A/Cheater control.

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).

The A/C compressor can be engaged by pressing the A/C (snowflake) button on the A/C-heater control. It will automatically engage 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/Cheater 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 duct, which is secured to the top of the instrument panel. The airflow from the defroster outlets is directed by fixed vanes in the defroster outlet grille and cannot be adjusted.

The side window demister outlets receive airflow from the HVAC housing through the defroster duct and molded plastic demister ducts, which are secured to the instrument panel support. The airflow from the side window demister outlets is directed by fixed vanes and cannot be adjusted. The demisters operate when the mode control is set in any Floor to Defrost position.

The instrument panel outlets receive airflow from the HVAC housing through a molded plastic center panel duct and two end 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 two center panel outlets. Each of these outlets can be individually adjusted to direct or shut off the flow of air leaving the outlets.

The front and rear floor outlets receive airflow from the HVAC housing through the front and rear floor ducts which are secured to each side of the HVAC housing. The rear seat ducts direct airflow beneath the carpet to the outlets located near the front of each rear seat foot well. None of the floor outlets can be adjusted.

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 front A/C system is designed for use of non-CFC, R-134a refrigerant and uses an A/C expansion valve (TXV) to meter the flow of refrigerant to the A/C evaporator. To maintain minimum evaporator temperature and prevent evaporator freezing, an evaporator temperature sensor input is supplied to the A/C-heater control.

In turn, the powertrain control module (PCM) cycles the A/C compressor clutch off and on as necessary to optimize A/C system performance and to protect the A/C system from evaporator freezing.

REAR SYSTEM

The rear heating-A/C system pulls interior air through the opening in the rear quarter interior trim panel and into the rear blower motor in the rear heater-A/C housing, then through the rear A/C evaporator. Air flow can be directed either through or around the rear heater core by adjusting the blend-air door with either the front or the rear temperature control (depending on the front A/C-heater control setting). The air flow is then directed to the floor or ceiling outlets depending on the mode selected by the mode control. Air flow velocity can be adjusted with the blower speed control located on either the front A/C-heater control or the rear A/C-heater control (depending on the front A/C-heater control setting).

The headliner air outlets receive airflow from the rear heater-A/C housing through the molded plastic ceiling duct, which connects to the headliner duct and headliner air outlets. Airflow direction from the headliner air outlets can be adjusted to direct or shut off the flow of air leaving the outlets.

The rear floor outlet receives airflow from the rear heater-A/C housing through the molded plastic floor distribution duct, which connects to the rear floor outlet located in the rear quarter interior trim panel. The airflow from the rear floor outlet is directed by fixed vanes in the outlet and air flow direction cannot be adjusted. The rear floor outlet is integral to the rear quarter interior trim panel.

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.