Description

HEATER AND AIR CONDITIONER
A manually controlled single zone type heating-air conditioning system, manually controlled dual zone type heating-air conditioning system, manually controlled three zone type heating-air conditioning system or an automatic controlled three zone type heating-air conditioning system is available on this model.

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 for more information before opening or
attempting any service to the engine cooling system.

RS/RG HVAC Housing:

All vehicles are equipped with a common heater, ventilation and air conditioning (HVAC) housing. The system combines air conditioning, heating, and ventilating capabilities in a single unit housing mounted within the passenger compartment under the instrument panel.

Based upon the system and mode selected, conditioned air can exit the HVAC 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 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 - 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, near the A-pillars.
- Panel Outlets - There are five panel outlets in the instrument panel, one located near each outboard end of the instrument panel facing the rear of the vehicle and three located near the top of the instrument panel center bezel.
- Front Floor Outlets - There are two front floor outlets, one located above each side of the center of the floor panel near the dash panel.

The heating and air conditioning systems pulls outside (ambient) air through the cowl opening at the base of the windshield and into the plenum chamber above the heating, ventilation and air conditioning (HVAC) housing, then through the evaporator coil. Air flow can be directed either through or around the heater core by adjusting the blend door with the temperature control knob on the A/C-heater control located on instrument panel. The air flow can then be directed out from the panel, floor and defrost outlets in various combinations using the mode control knob located on the A/C-heater control. Air flow velocity can be adjusted with the blower speed selector 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 system. 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. The temperature control knob 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.

On all models, the outside air intake can be shut off by pressing the Recirculation button on the A/Cheater 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 air conditioning 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 knob on the A/C-heater control is used to also direct the conditioned air to the selected system outlets. The mode control switch uses an electric motor to control the mode doors.

MANUAL SINGLE ZONE
The manual single zone heating and A/C system allows one temperature setting for the entire vehicle. The full range of temperatures that the system can produce are available by rotating the temperature control located on the A/C-heater control.

The A/C-heater control and integral computer is located in the instrument panel and contains:
- a rear window defogger on/off switch. Contains an LED that illuminates to show when the function is operational.
- an air recirculation on/off switch. The Recirculate button contains an LED that illuminates to show when the function is in operation.
- an air conditioning on/off switch. The Snowflake button contains an LED that illuminates to shown when the function is in operation.
- a rotary knob for fan speed selection and turning the heater-A/C system off.
- a rotary knob for temperature control of the discharged air.
- a rotary knob for mode control.

- The temperature control knob enables continuously variable proportioning of the conditioned air.
- The mode control knob enables continuously variable proportioning of air flow between modes and has detents adjacent to each icon.
- The blower control provides four separate speeds and an Off position.
- When the heater-A/C system is off, the HVAC computer closes the recirculation door to prevent outside air from entering the passenger compartment.
- Interior air may be recirculated to speed up heating or cooling in all modes except defrost and mix by pressing the Recirculate button on the A/C-heater control.
- To reduce humidity for rapid defogging, the A/C compressor runs automatically in modes from "mix" to full defrost when outside temperatures are above freezing.
- Air conditioning is available in any mode by pressing the snowflake, A/C on/off button.

MANUAL DUAL ZONE
The manual dual zone heating and A/C system allows completely independent side-to-side temperature control of the discharge air.

The A/C-heater control and integral computer is located in the instrument panel and contains:
- a rear window defogger on/off switch. Contains an LED that illuminates to show when the function is operational.
- slide controls for completely independent side-to-side temperature control of the discharged air. The full range of temperature that the system can produce in any mode is available on either side of the vehicle by independently positioning the slide controls on the instrument panel.
- an air recirculation on/off switch. The Recirculate button contains an LED that illuminates to show when the function is in operation.
- an air conditioning on/off switch. The Snowflake button contains an LED that illuminates to shown when the function is in operation.
- a rotary knob for fan speed selection and turning the heater-A/C system off.
- a rotary knob for mode control.

- The two slide controls enable continuously variable proportioning of the conditioned air.
- The mode control knob enables continuously variable proportioning of air flow between modes and has detents adjacent to each icon.
- The blower control provides four separate speeds and an Off position.
- When the heater-A/C system is off, the HVAC computer closes the recirculation door to prevent outside air from entering the passenger compartment.
- Interior air may be recirculated to speed up heating or cooling in all modes except defrost and mix by pressing the Recirculate button on the A/Cheater control.
- To reduce humidity for rapid defogging, the A/C compressor runs automatically in modes from "mix" to full defrost when outside temperatures are above freezing.
- Air conditioning is available in any mode by pressing the snowflake, A/C on/off button.

MANUAL THREE ZONE
The fully adjustable manual three zone front and rear heating and A/C system allows intermediate seat passengers the ability to regulate air temperature as well as fan speed and provides floor outlets to the rear of the right sliding door and overhead outlets at each rear outboard seating position. Primary control for the rear blower is on the front A/C-heater control. All controls are identified by ISO graphic symbols.

FRONT CONTROL PANEL
The front A/C-heater control and integral computer mounted in the instrument panel contains:
- a rear window defogger on/off switch.
- slide controls for completely independent side-to-side temperature control of the discharge air. The full range of temperature that the system can produce in any mode is available on either side of the vehicle by independently positioning the slide controls on the instrument panel.
- an air recirculation button. The Recirculate button contains an LED that illuminates to show when the function is in operation.
- an air conditioning button that allows the compressor to be turned on/off. The Snowflake button contains an LED that illuminates to shown when the function is in operation.
- a rotary knob for front fan speed selection and turning the heater-A/C system off.
- a rotary knob for rear fan speed selection.
- a rotary knob for mode control.

- Primary control of the rear heater-A/C system is on the instrument panel. This control allows the driver to set the rear compartment fan speed, to turn the rear heater-A/C system off, or to give control to the intermediate seat occupants by switching to the Rear position. When the rear heater-A/C system is controlled from the instrument panel, rear air temperature is based on the driver-side temperature control position, and the mode (floor or overhead air) is based on the front control's mode position.
- The mode control knob enables continuously variable proportioning of air flow between modes but has detents adjacent to each icon.
- The blower control provides four separate speeds and an Off position. When the heater-A/C system is off, the HVAC computer closes the recirculation door to prevent outside air from entering the passenger compartment.
- Interior air may be recirculated to speed up heating or cooling in all modes except defrost and mix by pressing the Recirculate button on the control panel.
- To reduce humidity for rapid defogging the A/C compressor runs automatically in modes from "mix" to full defrost when outside temperatures are above freezing.
- Air conditioning is available in any mode by pressing the snowflake, A/C on/off, button.

REAR CONTROL PANEL
The rear A/C-heater control centrally mounted in the headliner allows intermediate seat passengers to adjust rear air distribution, temperature and blower motor speed when the center knob on the front A/C-heater control is set to the Rear position. The rear A/C-heater control contains:
- a rotary adjustment knob for temperature.
- a rotary adjustment for fan speed control.

With the rear control active, temperature selection dictates the air distribution mode (floor or overhead air) of the rear unit: a cool temperature setting directs flow to the overhead outlets and a warm temperature setting to the floor.

AUTOMATIC TEMPERATURE CONTROL (ATC)
Two different automatic temperature control (ATC) heating-A/C systems are available for this model depending on the market.

The Dual-Zone ATC system allows the driver and front occupants to each select individual comfort temperatures.

The Three-Zone ATC system allows both the driver and front occupants and the rear intermediate occupants to select individual comfort temperatures.

NOTE: Individual comfort temperatures are the perceived temperature level at the individual seating areas, NOT the actual passenger compartment air temperature.

The ATC system includes a particulate air filter. The filter element is the same size as the A/C evaporator to ensure ample capacity. A door at the base of the HVAC housing below the glove box provides easy access to the filter element.

The ATC computer utilizes integrated circuitry and information carried on the programmable communications interface (PCI) data bus network to monitor many sensors and switch inputs throughout the vehicle. In response to those inputs, the internal circuitry and programming of the ATC computer allow it to control electronic functions and features of the ATC system. The inputs to the ATC computer are:
- Vehicle Speed/Engine RPM - The ATC computer monitors engine rpm, vehicle speed and manifold absolute pressure information from the powertrain control module (PCM).
- Coolant Temperature - ATC computer monitors coolant temperature received from the PCM and converts it to degrees Fahrenheit.
- Ambient Temperature - ATC computer monitors ambient temperature from the compass mini trip computer (CMTC) and converts it to degrees Fahrenheit.
- Engine Miscellaneous Sensor Status - ATC computer monitors A/C disable information from the PCM.
- Refrigerant Pressure - ATC computer monitors barometric pressure, intake air temperature, high side pressure and methanol content as broadcast by the PCM.
- Door Ajar Status - The ATC computer monitors driver front door, passenger front door, left rear door, right rear door and liftgate ajar information, as identified by the body control module (BCM), to determine if all in-car temperatures should be maintained.
- Dimming - The ATC computer monitors dimming status from the BCM to determine the required level of brightness and will dim accordingly.
- Vehicle Odometer - The ATC computer monitors the vehicle odometer information from the BCM to prevent flashing the vacuum-fluorescent (VF) digital display icons if the manual motor calibration or manual cool down tests have failed. Flashing of the display icons will cease when the vehicle odometer is greater than 3 miles.
- English/Metric - The ATC computer monitors the English/Metric information broadcast by the CMTC. The set temp displays for both the front and rear control heads will be set accordingly.
- Vehicle Identification Number - The ATC computer monitors the last eight characters of the VIN broadcast by the PCM and compares it to the information stored in EEPROM. If it is different, the new number will be stored over the old one and a motor calibration shall be initiated.
- A/C System Information - The ATC computer will send a message for evaporator temperature too low, fan blower relay status, evaporator sensor failure, rear window defogger relay and A/C select.

Comfort temperature or perceived temperature is affected by air flow, sun levels on exposed skin, etc. The air temperature may be higher or lower than the comfort temperature. The automatic temperature control (ATC) system uses two infrared sensors in the instrument panel center stack to measure the temperature of the front occupants in order determine their comfort level relative to their selected comfort temperature. The integral HVAC computer adjusts temperature and air flow rates to maintain the customer-perceived comfort temperatures. The air temperature in the passenger compartment may be slightly higher or lower than the comfort temperature at any time. For instance, on sunny summer days the air flow will probably be cooler than the comfort temperature; on cold or cloudy days and at night it will probably be slightly warmer.

The Three-Zone ATC system uses the infrared sensors located in the instrument panel center stack along with an offset calibration strategy to meet the comfort requirements of the rear seat occupants.

FRONT CONTROL PANEL
The front A/C-heater control and integral computer is mounted in the instrument panel and contains:
- a power button which allows the system to be completely turned off. The display is blank when the system is off.
- a rocker switch that selects a cool-down rate. LO-AUTO or HI-AUTO are displayed when the system is in automatic operation.
- three rocker switches that select comfort temperatures from 15° to 30° C (59° to 85° F), which are shown in the VF digital display. If the set temp is 15° C (59° F) and the down button is pressed, the set temp value will become 13° C (55° F) but the display will show LO. If the set temp is 29° C (85° F) and the up button is pressed, the set temp value will become 32° C (90° F) but the display will show HIGH. Temperatures can be displayed in either metric or Fahrenheit, which is controlled from the overhead console.
- an air conditioning button that allows the compressor to be turned off. A Snowflake symbol is illuminated when air conditioning is on, whether under manual or automatic control.
- an air recirculation button. A Recirculation symbol appears in the display when the button is pressed, or when the system exceeds 80 percent recirculated air under automatic control due to high air conditioning demand.
- a rear window defogger on/off switch. A graphic symbol shows when the defroster is on.
- a rotary knob for front fan speed selection can override the automatic controls. LEDs surrounding the knob show the current setting.
- a rotary knob for control of the rear system (Three-Zone ATC system only).
- a rotary knob for mode control can override the automatic controls. LEDs surrounding the knob show the current setting.
- computer logic which remembers the settings of the controls when the ignition is turned off and retains those settings after a restart. If the system is off when the ignition is turned off it will be off when the engine is restarted, etc.
- computer logic which provides variable air recirculation under high temperature and humidity conditions. Because recirculation is generally accompanied by increased fan noise, the proportion of recirculated to outside air gradually approaches full recirculation over a broad temperature range.
- computer logic which enables additional heat for diesel equipped vehicles by using a supplemental engine coolant heater.

- AUTO HI/LO - This system features two sets of automatic control logic that allow either a rapid cool-down rate or a somewhat slower cool-down rate with less fan noise. HI-AUTO controls the system to reach its assigned temperature quickly with a higher fan speed. LO-AUTO controls the system to reach its assigned temperature somewhat slower with less fan noise. Both modes will automatically engage auto recirculation.
- DEFROST - The defrost function must be manually selected to direct air flow to the windshield to remove fog or ice. The ATC system cannot automatically sense the presence of fog or ice on the windshield.
- RECIRC - The RECIRC button will close the air inlet door. If the system is in auto recirc (indicator being displayed automatically), pressing the manual recirc button will disable the auto recirc function until one of the auto keys are pressed or the ignition is cycled. If Auto HI/LO is pressed while manual recirc is active, manual recirc will be deactivated.
- REAR WINDOW DEFOGGER - Pushing the button sends a PCI bus message to the intelligent power module which controls the rear window defogger and side view mirror (if equipped) circuitry. The defogger function will be active for 10 minutes and can be turned off by a switch press. The defogger will function while the control is in the ON mode.
- FAN/MODE - The Fan and Mode knobs have 17 manual selectable positions. Manually changing either of the rotary knobs for mode or fan speed settings makes control of that blower motor manual. If only one is changed manually, the other remains under automatic control. Pressing the HI-AUTO/LO-AUTO rocker switch restores full automatic control.
- BLOWER DELAY TIMER - The word DELAY is displayed at start-up to signify that the system is waiting so that cold air will not be blowing. This tells the operator that it is unnecessary to turn the system off, raise the temperature setting or turn the fan speed setting down to prevent cold air from blowing. A countdown in minutes and seconds until the engine is warm enough to begin delivering heat to the passengers alternates with the DELAY message at 25 second intervals. This countdown is based on actual measurement of the rate of engine coolant temperature change. During the delay time, mix mode is selected and the fan operates at a low speed to keep the windshield fog free.
- REAR CONTROL (Three-Zone only) - When the Rear System control knob is moved to the OFF position, there will be a delay of approximately 1 second before the system actually turns off. This delay is to prevent an undesired blower dropout if the knob is moved through OFF to the other selections.

REAR CONTROL PANEL THREE ZONE ATC SYSTEM
The Three-Zone ATC System utilizes a rear control panel centrally mounted on the headliner which includes a VF digital display, a rocker control for temperature and rotary controls for adjustment of mode and fan speed of the rear heating-A/C system by intermediate seat passengers.

Primary control of the rear compartment heating-A/C system for the Three-Zone ATC system is in the instrument panel center stack. This control allows the driver to turn the rear heating-A/C system off, or allows the intermediate seat occupants control of the rear system by switching to the REAR position, or provides fully automatic control based on the temperature setting shown on the front control display.
- REAR CONTROL - Selecting automatic control of the rear unit at the instrument panel, illuminates a Locked Padlock in the rear control panel display. Selecting REAR activates the rear control panel and the Padlock then appears unlocked.
- FAN KNOB - The rear fan control has Off and AUTO positions and a range of manual speed settings that override the AUTO setting.
- MODE KNOB - The mode control allows intermediate seat occupants to manually override the automatic mode and select any balance of air flow between overhead and floor outlets from full overhead to full floor.
- SET TEMP - The rear set temp control will operate identical to the front controls. If the front control rear set temp button is pressed simultaneously with the rear control head, then the front control head press events shall have priority, i.e. if the front user presses Rear Set Temp down and the rear user presses Set Temp up, then the rear set temp will decrease.