Heating and Air Conditioning: Description and Operation
HVACDESCRIPTION
A manual temperature control (MTC) single zone type heating-A/C system or a manually controlled heater-only system is standard equipment on this model, depending on market.
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 System before opening or attempting any service to the engine cooling system.
All vehicles are equipped with a common heater, ventilation and air conditioning (HVAC) housing (1). The heating-A/C system combines heating, ventilating and A/C (if equipped) capabilities in a single HVAC housing mounted within the passenger compartment beneath the instrument panel. The HVAC housing includes:
- Mode-air doors (2)
- A/C evaporator (A/C system only) (3)
- Recirculation-air door and actuator (A/C system only) (4)
- Blower motor (5)
- Mode control cable (6)
- Temperature control cable (7)
- Heater core (8)
- Blend-air door (9)
On heater-only systems, the A/C evaporator is omitted from the HVAC housing and is replaced with an air restrictor plate.
Based upon the system mode selected, conditioned air can exit the standard heater-only or optional heater-A/C 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 air distribution housing and the floor outlets are located on each side of the distribution housing. Once the conditioned air exits the HVAC housing, it is further directed through molded plastic ducts to the various 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 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 on each side of the center tunnel near the dash panel.
- Rear Floor Outlets - There are two rear floor outlets, one located on each side of the floor panel center tunnel near the front of each rear seat foot well.
A heater booster is used to aid in warming the engine coolant on vehicles equipped with the 2.2 liter diesel engine. The heater booster system is switched on while the vehicle is being driven to help the engine reach its normal operating temperature quickly and to help aid in heating up the air within the passenger compartment quickly when requested by the operator.
OPERATION
Both the manual temperature control (MTC) heating-A/C system and the heater-only system 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. The temperature control determines the discharge air temperature by operating the blend door cable, which moves the blend-air door. This design allows almost immediate control of output air temperature.
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. On models equipped with A/C, the air passes through the A/C evaporator (3). Air flow can be directed either through or around the heater core (1). This is done by adjusting the blend-air door (2) with the temperature control located on the A/C-heater control in the instrument panel. The temperature control uses a cable to operated the blend-air door. Air flow is 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 is adjusted with the blower speed control located on the A/C-heater control.
On models equipped with A/C, the outside (fresh) air intake can be shut off by pressing the Recirculation button on the A/C-heater control. This will operate an electrically actuated recirculation-air door (4) that closes off the fresh air intake and recirculates the air that is already inside the vehicle. Fresh air intake cannot be controlled on vehicles without A/C (heater-only system uses outside air at all times).
The A/C compressor is engaged by pressing the A/C (snowflake) button on the A/C-heater control with the blower motor control in any position except off and, will automatically engage when the mode control is set in the Mix or Defrost positions. This removes 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 then used to direct the conditioned air to the selected system outlets. The mode control uses a control cable to operated the mode-air doors (5 and 6).
The defroster directs air to the inside base of the windshield through the outlet located in the top center of the instrument panel. The defroster outlet receives airflow from the HVAC housing through the molded plastic defroster duct, which is secured to the instrument panel top. 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 demisters direct air to the front side windows through outlets located on the top corners of the instrument panel. The demister outlets receive airflow from the HVAC housing through the defroster duct and two molded plastic demister ducts. 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 top cover. The demisters operate when the mode control is anywhere between floor and defrost settings. Some air may be noticeable from the demister outlets when the mode control is in the bi-level to floor positions.
The left and right panel outlets receive airflow from the HVAC housing through a molded plastic air distribution duct and the center air outlets directs airflow from the distribution duct to the two center panel outlets. The airflow from each of the panel outlets is adjustable by rotating the outlet in any direction.
The front and rear 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. A molded plastic rear seat duct elbow is fitted to the bottom of the floor distribution duct and directs airflow through a molded plastic duct beneath the carpet on the right side of the floor panel center tunnel to the right rear floor outlet. The right floor duct also features a crossover fitting that joins the right floor duct to the left floor duct over the top of the floor panel center tunnel to direct airflow to the left rear floor outlet. None of the floor outlets can be adjusted.