Blend Air System Overview
Blend Air System Overview
The standard front and available rear HVAC 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 controls determines 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.
The standard front HVAC 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 housing and then 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 controls located on the HVAC 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 HVAC 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 HVAC control.
The fresh air intake can be shut off by pressing the Recirculation button on the HVAC 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 button on the HVAC 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 HVAC control is used to direct the conditioned air to the selected system outlets.
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 outlets receive airflow from the HVAC housing through the molded plastic ducts. The direct air from the HVAC housing through the outlets located on the top corners of the instrument panel. The airflow from the side window outlets is directed by fixed vanes in the outlet grilles and cannot be adjusted. The side window outlet grilles are serviceable from the instrument panel. The 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 bottom of the HVAC housing. Two plastic rear floor distribution ducts attach to the housing and provide conditioned air to the intermediate seating positions. The floor outlets cannot be adjusted.
• 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 HVAC 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 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 HVAC control. In turn, the powertrain control module 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.