Heating And Air Conditioning - Operation

OPERATION

The heating and 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 Dual Zone system, separate blend-air doors are used to 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 output air temperatures.






NOTE: Typical blend air system shown.

The heating and 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 doors (3) with the temperature controls on the switchbank or the U-Connect Touch (TM) screen module. 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 controls on the switchbank or the U-Connect Touch (TM) screen module. The temperature and mode controls use electrical actuators to operated the air doors.

The velocity of the air flow out of the outlets can be manually or automatically adjusted, depending on the system. using the blower motor control on the switchbank or the U-Connect Touch (TM) screen module.

The fresh air intake can be shut off by pressing the Recirculation button on the switchbank or the U-Connect Touch (TM) screen module. 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 switchbank or the U-Connect Touch (TM) screen module. The A/C compressor will automatically engage based on humidity sensor readings to help prevent windshield fogging.

The defroster outlets receive airflow from the HVAC housing through the molded plastic defroster duct, which is secured to the top of the HVAC housing. The airflow from the defroster duct 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 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 module. In turn, the Powertrain Control Module (PCM) cycles the A/C clutch on and off as necessary to optimize A/C system performance and to protect the A/C system from evaporator freezing.