Description - Automatic Three Zone

AUTOMATIC THREE ZONE
The automatic temperature control (ATC), three zone, front and rear heating and air conditioning 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 air conditioning 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-flourescent (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.