Heating and Air Conditioning: Description and Operation
ENGINE COOLING SYSTEMTo maintain the performance level of the heating-A/C system, the engine cooling system must be in proper working order. 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.
HEATER AND AIR CONDITIONER SYSTEM
A manually controlled single zone type heating-air conditioning system or a manually controlled heater-only system is available as standard equipment on this model (depending on market).
Blend-Air HVAC System - Typical:
All vehicles are equipped with a common heater, ventilation and air conditioning (HVAC) housing. The system combines air conditioning, heating and ventilation capabilities in a single unit mounted within the passenger compartment under the instrument panel. The HVAC housing includes:
- Blower motor
- Blower motor resistor
- Recirculation-air door and actuator (A/C system only)
- Heater core
- A/C evaporator (A/C system only)
- Mode-air door
On heater-only systems, the evaporator coil is omitted from the 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 unit housing through one or a combination of the three main housing outlets: defrost, panel or floor. The defrost outlet is located on the top of the housing, the panel outlet is located on the face of the housing and the floor outlet is located on the bottom of the housing. Once the conditioned air exits the unit housing, it is further directed through molded plastic ducts to the various outlets in 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 four front floor outlets, two located above each side of the floor panel 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.
The heating-A/C 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. On models equipped with A/C, the air passes 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. There are 17 different mode selections possible. Air flow velocity can be adjusted with the blower speed control.
On models equipped with A/C, the ambient air intake can be controlled by opening and closing the recirculating air door. When placed in the Recirculation position, air that is inside the vehicle is continuously recirculated through the HVAC housing. Ambient air cannot be controlled on vehicles without A/C. The system uses outside air at all times.
The A/C compressor can be engaged by turning the blower motor control counterclockwise from the Off position. 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 defroster outlet receives airflow from the HVAC housing through the molded plastic defroster duct, which is snapped onto the HVAC housing defroster outlet and secured by two tabs to mounting slots in the instrument panel top cover. 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 demister outlets receive airflow from the HVAC housing through the air outlet distribution duct, two molded plastic demister hoses and, on the right side only, an intermediate duct. The air outlet distribution duct is secured to the instrument panel with screws and receives airflow through the panel outlet of the HVAC housing. 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 top cover. 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 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 panel outlets also receive airflow from the HVAC housing through the air outlet distribution duct. Molded plastic panel outlet ducts and, on the left side only, an intermediate elbow direct airflow from the distribution duct to the outboard panel outlets, while a center air outlet duct directs airflow from the distribution duct to the two center panel outlets. The airflow from each of the panel outlets is adjustable. A knob in the center of each panel outlet grille is used in a joystick fashion to adjust a center diffuser that changes the airflow direction, and a knob on the outer edge of each panel outlet grille opens or closes a shutter to turn airflow on or off through that outlet.
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.