Heating and Air Conditioning: Description and Operation: Description and Operation
HEATING AND AIR CONDITIONINGDESCRIPTION
A manually controlled or an automatic controlled single zone type heating-air conditioning system is available on this model.
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.
Common Blend-Air HVAC System:
All vehicles are equipped with a common heater, ventilation and air conditioning (HVAC) housing. The heating-A/C system combines A/C, heating, and ventilating capabilities in a single HVAC housing mounted within the passenger compartment behind the instrument panel. The HVAC housing includes:
- Blower motor
- Blower motor resistor or power module (depending on application)
- Heater core
- A/C evaporator
- Evaporator temperature sensor
- Blend-air door and actuator
- Mode-air door and actuator
- Recirculation-air door and actuator
Based upon the mode selected, conditioned air can exit the HVAC housing through one or a combination of the three main housing outlets: defrost, panel or floor. The defrost and panel outlets are 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, near the A-pillars.
- Panel Outlets - There are four 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 near the top of the instrument panel center bezel.
- Front Floor Outlets - There are two front floor outlets, one located above each side of the center of the floor panel near the dash panel.
- Rear Floor Outlets - There are two rear floor outlets, one located on each side of the floor console near the rear of each front seat.
OPERATION
The 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. A temperature control on the A/C-heater control is used to adjust the discharge air temperature. The A/C-heater control sends a request signal to the body control module (BCM) to move the electric blend door actuator(s), which operate the blend-air door(s). This allows an almost immediate control of the output air temperature of the system. The A/C system is 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.
The 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 direct the conditioned air to the selected system outlets. The A/C-heater control sends a request signal to the BCM to operate the electric door actuators.
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 serviceable from the instrument panel.
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 demisters operate when the mode control is positioned in the bi-level, floor, floor-defrost and defrost settings. The airflow from the side window demister outlets is directed by fixed vanes in the demister outlet grilles and cannot be adjusted. The demister outlet grilles are only serviced with the instrument panel top cover.
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 two 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 duct. The front floor outlets are integral to the molded plastic floor distribution duct, which is secured to the bottom of the HVAC housing. The floor outlets cannot be adjusted.
This A/C system uses an A/C expansion valve to meter the flow of refrigerant to the A/C evaporator. To maintain minimum evaporator temperature and prevent evaporator freezing, an evaporator temperature sensor is used to supply evaporator temperature input to the BCM. The powertrain control module (PCM) cycles the A/C compressor clutch off and on as necessary to protect the A/C system from evaporator freezing and optimize A/C system performance.