Automatic Temperature Control (ATC)

THREE ZONE AUTOMATIC TEMPERATURE CONTROL
The Three-Zone Automatic Temperature Control (ATC) allows occupants to select a comfort temperature, which is the perceived temperature level not the actual passenger compartment air temperature.

The Three Zone Automatic Temperature Control system includes a dust and odor air filter. The filter element is the same size as the air conditioning evaporator to ensure ample capacity. A door at the base of the heater and air conditioning 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 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 VF tube 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 impinging on exposed skin, etc. The air temperature may be higher or lower than the comfort temperature. Three infrared sensors, two in the instrument panel center stack, and one in the overhead-mounted rear control panel, independently measure the temperature of the driver, front passenger, and rear compartment occupants to determine their comfort level relative to the selected comfort temperature. The HVAC computer in the control module adjusts the air flow rate and temperature to maintain the customer-perceived comfort temperature. The air temperature in the passenger compartment at any time may be slightly higher or lower than the comfort temperature. 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. Infrared Three-Zone Temperature Control provides side-to-side and front-to-rear variation in comfort temperature settings. The Infrared Three- Zone Automatic Temperature Control fan provides a continuously variable air flow rate to meet occupant comfort requirements.

Front Control Panel
The front control panel and integral computer is mounted in the instrument panel.

The instrument panel mounted control and integral computer contains:
- A power button which allows the system to be completely turned OFF. The display is blank when the system is OFF.
- Three rocker switches that select comfort temperatures from 15 - 30 °C (59 - 85 °F), which are shown in the vacuum-fluorescent digital control display. If the set temp is 59 and the down button is pressed, the set temp value will become 55 but the display will show LO. If the set temp is 85 and the up button is pressed, the set temp value will become 90 but the display will show HIGH. Temperatures can be displayed in either metric or Fahrenheit, which is controlled from the overhead console.
- A rocker switch that selects a cool-down rate. LO-AUTO or HI-AUTO are displayed when the system is in automatic operation.
- A defroster button which turns ON the defroster independently during full automatic control. A defroster symbol illuminates in the display when the button is pressed.
- Air recirculation button. A Recirculation symbol appears in the display when the button is pressed, or when the system exceeds 80 percent circulated air under automatic control due to high air conditioning demand.
- Rear window defogger On/Off switch. A graphic symbol shows when the defroster is on.
- 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.
- Rotary knob for front fan speed selection can override the automatic controls. LEDs surrounding the knob show the current setting.
- Rotary knob for control of the Rear system.
- A rotary knob for mode control can override the automatic controls. LEDs surrounding the knob show the current setting.
- Computer logic 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 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.
- A graphic symbol of the windshield that illuminates when the windshield wiper deicer is active.
- 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.
- DE-FROST - The front de-frost function is active when the rear window defogger function is active or when the defog/defrost mode is selected.
- 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 OFF 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 function alone manual for as long as the ignition is ON. If only one is changed manually, the other remains under automatic control. Pressing the HI-AUTO/LO-AUTO rocker switch restores full automatic control.
- REAR CONTROL - 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.
- 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, Defrost mode is selected and the fan operates at a low speed to keep the windshield fog free.

Rear Control Panel
A rear control panel centrally mounted on the headliner includes a vacuum-flourescent digital display a rocker control for temperature and rotary controls for adjustment of mode and fan speed control of the rear unit by intermediate seat passengers.

Primary control of the rear compartment unit is in the instrument panel center stack. The rear unit control knob there allows the driver to turn the rear unit off, allow control by the intermediate seat occupants by switching to the REAR position, or provide 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.