Operation - Heater And Air Conditioner

WARNING: This page is about a different car, the 2004 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.

The heating and air conditioning system pulls outside (ambient) air through the cowl opening at the base of the windshield, then into the plenum chamber above the heating, ventilation and air conditioning (HVAC) housing and through the evaporator coil. Air flow can be directed either through or around the heater core. This is done by adjusting the blend door with the temperature control knob on the A/C-heater control located 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 heater and air conditioning system is a blend-air type systems. In a blend-air system, a blend 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 actuating an electric motor, which operates the blend door. This allows an almost immediate control of the output air temperature of the system.

The outside air intake can be shut off by selecting the Recirculation Mode with the mode control. This will operate a electric actuated recirculation air door that closes off the outside 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/Cheater control is used to also direct the conditioned air to the selected system outlets. The mode control uses an electric motor to control the mode 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 outlets is directed by fixed vanes in the defroster outlet grilles and cannot be adjusted. The defroster outlet grilles are 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 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 integral to the instrument panel. 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 floor-defrost and defrost-only settings. Some air may be noticeable from the demister outlets when the mode control is in the bi-level to floor positions.

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 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.

The A/C system is designed for the use of non-CFC, R-134a refrigerant. The A/C system has an evaporator coil to cool and dehumidify the incoming air prior to blending it with the heated air. This A/C system uses a fixed A/C orifice tube in the liquid line near the condenser outlet to meter refrigerant flow to the A/C evaporator. To maintain minimum evaporator temperature and prevent evaporator freezing, an evaporator temperature sensor is used. The power-train control module (PCM) is programmed to respond to the evaporator temperature sensor input by cycling the A/C compressor clutch as necessary to optimize A/C system performance and to protect the A/C system from evaporator freezing.