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Heating And Air Conditioning - Operation






OPERATION

All the available heating-A/C systems are blend-air type systems. In the front dual zone blend-air heating-A/C systems, two blend-air doors control the amount of conditioned air that is allowed to flow through, or around the heater core. The two blend-air doors provide completely independent side-to-side temperature control of the discharge air. The temperature controls determine the discharge air temperatures by operating the blend door actuators, which move the blend-air doors. This design allows almost immediate control of the output air temperatures. Both of the available rear heating-A/C systems are single zone blend-air systems, with one blend air door.

FRONT SYSTEM






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 uses electrical actuators to operate 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/C-heater 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) located within the passenger compartment.

The A/C compressor can be engaged by pressing the A/C (snowflake) button on the Manual Temperature Control (MTC) A/C-heater control or is automatically engaged on the Automatic Temperature Control (ATC) system when set temperatures require conditioned air cooling. On both systems, the A/C compressor will automatically engage when 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 two slot-type defroster outlets receive airflow from the HVAC housing through the molded plastic defroster ducts, which connect to the HVAC housing defroster outlets. The airflow from the defroster outlets is directed by fixed vanes in the defroster outlet grilles and cannot be adjusted. The defroster outlet grilles are serviceable from the instrument panel top cover.

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 A-pillars. The airflow from the side window demister outlets is directed by fixed vanes in the demister outlet grilles and cannot be adjusted. The side window demister outlet grilles are not serviceable from the A-pillars. The demisters operate when the controls are in Heat, Bi-level, Mix and Defrost modes.

The four instrument panel outlets receive airflow from the HVAC housing through two molded plastic main panel ducts. One duct directs air flow out of the right side instrument panel outlets, while the other duct delivers air flow to the left side 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 which are connected to the rear of the HVAC air distribution housing. Two plastic rear distribution ducts and one center console duct attach to the rear of the air distribution housing and provide conditioned air to the rear seating positions. The airflow from the two rear distribution ducts cannot be adjusted. The two outlets located at the rear of the floor console can be individually adjusted to direct the flow of air, but the outlets on either side of the console cannot be adjusted and air flow is directed by fixed vanes.

NOTE: It is important to keep the HVAC 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 the use of non-CFC, R-134a refrigerant and uses an A/C expansion valve to meter the flow of refrigerant to the A/C evaporator. The A/C evaporator cools and dehumidifies the incoming air prior to blending it with the heated air. To maintain minimum evaporator temperatures and prevent evaporator freezing, an evaporator temperature sensor is used. This sensor is located downstream of the evaporator and supplies an evaporator temperature signal to the A/C-heater control.

REAR SYSTEM

The rear heating-A/C system pulls interior air through the opening in the rear quarter trim panel and into the rear blower motor, located in the rear heater-A/C housing. Then the air is pushed 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 temperature selected. 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 molded plastic ceiling ducts, which connect to the headliner duct and air outlets. Airflow direction from the headliner air outlets can be adjusted by moveable vanes.

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

The rear A/C system is also designed for use of non-CFC, R-134a refrigerant, and uses an expansion valve to meter the flow of refrigerant to the rear A/C evaporator.

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