HVAC - SERVICE INFORMATION
DESCRIPTION
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 7 - Cooling for more information 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 A/C, heating, and ventilating capabilities in a single HVAC housing mounted within the passenger compartment beneath the instrument panel. The HVAC housing includes:
- Recirculation-air door and actuator (2)
- Blower motor (3)
- Blower motor resistor (4)
- Heater core (5)
- Mode control cable (6)
- Blend-air door (7)
- Temperature control cable (8)
- Evaporator temperature sensor (A/C only) (9)
- Mode-air doors (10)
- A/C evaporator (A/C system only) (11)
On heater-only systems, the A/C evaporator is omitted from the HVAC housing and is replaced with an air restrictor plate.
NOTE: An electric positive temperature coefficient (PTC) heater is used on vehicles when equipped with the 2.8L diesel engine. The PTC heater unit compensates for the lower engine coolant temperatures produced by the diesel engine. The PTC heater unit is mounted in the HVAC air distribution housing, downstream of the heater core. For more information, (refer to 24 - HEATING & AIR CONDITIONING/CABIN HEATER/HEATER UNIT - DESCRIPTION).
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, 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 the floor panel center tunnel behind the instrument panel.
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-air door. This design allows almost immediate control of output air temperature.
NOTE: Typical blend-air type HVAC system shown.
The heating-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 when equipped with A/C, 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 (3) with the temperature control located on the A/C-heater 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 A/C-heater control. The temperature and mode control uses cables 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 A/C-heater control.
NOTE: Recirculation mode will not operate when in the Floor, Mix or Defrost position and the recirculation indicator lamp will not illuminate.
The fresh air intake can be shut off by pressing the Recirculation button on the A/C-heater control when the control is set to Panel mode. 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.
When equipped with A/C, the A/C compressor can be engaged by pressing the A/C (snowflake) button on the A/C-heater control. It will automatically engage when the mode control is set in any Floor 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 A/C-heater 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 is secured to the top of the instrument panel. The airflow from the defroster outlet 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. 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 cover and direct air from the HVAC housing through the outlets on the top corners of the instrument panel. The demisters operate when the mode control is set in any Floor to Defrost position.
The panel outlets receive airflow from the HVAC housing through the center air distribution duct and molded plastic panel outlet ducts. The airflow direction from each of the panel outlets can be adjusted by rotating the outlet and/or moving the shutters which are integral to each outlet. Airflow can be turned on or off through each outlet by closing the shutters completely.
The front floor receives airflow from the HVAC housing through molded plastic front floor ducts which are secured to each side of the HVAC air distribution housing. The airflow direction from the floor outlets can not be adjusted.