Heating and Air Conditioning: Description and Operation

A manual temperature control (MTC) single zone type heating-A/C system, MTC front and rear heating-A/C system or a fully adjustable automatic temperature control (ATC) front and rear heating-A/C system is available on this vehicle.

To maintain the performance level of the heating, ventilation and air conditioning (HVAC) system, the engine cooling system must be properly maintained. The use of a bug screen is not recommended. Any obstructions in front of the radiator or A/C condenser will reduce the performance of the A/C and engine cooling systems.

The engine cooling system includes the radiator, thermostat, radiator hoses and the engine coolant pump. Refer to Cooling for more information before opening or attempting any service to the engine cooling system.

FRONT HEATING AND A/C SYSTEM




All vehicles are equipped with a common front heater, ventilation and air conditioning (HVAC) housing (1). The front heating-A/C system combines A/C, heating, and ventilating capabilities in a single HVAC housing mounted within the passenger compartment under the instrument panel. The front HVAC housing includes:
- Recirculation-air door and actuator (2)
- Blower motor (3)
- Blower motor resistor block (MTC) or blower motor power module (ATC) (4)
- Evaporator temperature sensor (5)
- Blend-air door and actuator (6)
- Mode-air doors and actuators (7)
- Heater core (8)
- A/C evaporator (9)

Based upon the mode selected, conditioned air can exit the front HVAC housing through one or a combination of the three main housing outlets: defrost, panel or floor. The defrost outlet is located on the top of the HVAC housing, the panel outlet is located on the top of the HVAC housing and the floor outlet is located on the bottom of the HVAC housing. Once the conditioned air exits the HVAC housing, it is further directed through molded plastic ducts to the outlets within the vehicle interior. These outlets and their locations are as follows:
- Defroster Outlet - A single large defroster outlet is located in the center of the instrument panel top cover, near the base of the windshield.
- Side Window Demister Outlets - There are two side window demister outlets, one is located at each outboard end of the instrument panel top cover, near the belt line at the A-pillars.
- Panel Outlets - There are six panel outlets in the instrument panel, one located near each outboard end of the instrument panel facing the rear of the vehicle and two located at each side of the instrument panel center bezel.
- Floor Outlets - There are four floor outlets, one located above each side of the floor panel center tunnel near the dash panel and one behind each front seat.

REAR HEATING AND A/C SYSTEM




The manual temperature control (MTC) front and rear heating-A/C system, and the automatic temperature control (ATC) front and rear heating-A/C system are equipped with a common rear heater and A/C housing (1) that combines A/C and heating capabilities into a single unit mounted within the passenger compartment behind the right quarter interior trim panel. The rear HVAC housing includes:
- Blower motor (2)
- Blower motor resistor block (3)
- A/C evaporator (4)
- A/C expansion valve (5)
- Heater core (6)
- Blend door and actuator (7)
- Mode door and actuator (8)

Based upon the rear temperature selected, conditioned air can exit the rear HVAC housing through one or a combination of the two rear HVAC housing outlets: ceiling or floor. The ceiling outlet is located at the top-front of the HVAC housing and the floor outlet is located at the front of the HVAC housing. Once the conditioned air exits the rear HVAC housing, it is further directed through molded plastic ducts to the outlets at the rear of the passenger compartment. These outlets and their locations are as follows:
- Ceiling Outlets - There are four ceiling outlets in the headliner. One located at each outboard side of the intermediate seat position and one located in front of each rear seat position.
- Floor Outlet - There is one floor outlet in the right quarter interior trim panel located behind the right rear door area.

The standard front and the optional rear heating-A/C systems 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. A temperature control determines the discharge air temperature by operating an electric actuator, which operates the blend-air door. This allows an almost immediate control of the output air temperature of the systems. Both the front and rear A/C systems are designed for the use of non-CFC, R-134a refrigerant and use an A/C evaporator to cool and dehumidify the incoming air prior to blending it with the heated air.

FRONT SYSTEM
The front heating-A/C system pulls outside (ambient) air through the cowl opening at the base of the windshield, then into the air inlet housing above the heating, ventilation and air conditioning (HVAC) housing and through the A/C evaporator. Air flow can be directed either through or around the heater core. This is done by adjusting the blend-air door with the temperature control located on the A/C-heater control in the instrument panel. The air flow can then be directed from the panel, floor and defrost outlets in various combinations using the mode control located on the A/C-heater control. Air flow velocity can be adjusted with the blower speed control located on the A/C-heater control.

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 outside (fresh) air intake can be shut off by selecting the Recirculation Mode with the mode control. This will operate an electrically actuated recirculation-air door that closes off the fresh air intake and recirculates the air that is already inside the vehicle.

The A/C compressor can be engaged in any mode by pressing the snowflake, A/C on/off button. 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 mode control on the A/C-heater control is used to also direct the conditioned air to the selected system outlets. The mode control uses an electric actuator to control the mode-air doors.

The defroster outlet receives airflow from the HVAC housing through the molded plastic defroster duct, which connects to the HVAC housing defroster outlet. The airflow from the defroster outlet is directed by fixed vanes in the defroster outlet grille and cannot be adjusted. The defroster outlet grille is integral to 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 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 side window demister outlet grilles are serviceable from the instrument panel. 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 a molded plastic main panel duct, 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 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. Two plastic rear floor distribution ducts attach to the floor distribution duct and provide conditioned air to the intermediate seating positions. The floor outlets cannot be adjusted.

This A/C system 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 HVAC housing, then through the rear A/C evaporator. Air flow can be directed either through or around the rear heater core. This is done 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 automatically directed to the floor or ceiling outlets depending on the conditioned air temperature selected by the rear mode-air door. 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 HVAC 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 by moveable vanes and the headliner air outlets can be serviced separately.

The rear floor outlet receives airflow from the rear HVAC 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.

This rear A/C system uses an "H" valve-type thermal expansion valve (TXV) to meter the flow of refrigerant to the rear A/C evaporator.