Description

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.

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.

REAR CONTROL PANEL

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.