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Automatic Temperature Control (ATC)

AUTOMATIC TEMPERATURE CONTROL (ATC)

CAUTION: Automatic Temperature Control (ATC) Modules with software versions 41 and 0A used in 2001 and 2002 RS/RG vehicles are NOT compatible with software versions 13 and OF used in 2003 RS/RG vehicles. Do NOT install an ATC Module with software version 41 or 0A in a 2003 RS/RG vehicle or an ATC Module with software version 13 or 0F in a 2001 or 2002 RS/RG vehicle. Use the DRBIII(R) to verify which version software the ATC Module is using by selecting Body Systems, Automatic Temperature Control, and then selecting Module Display.

SYSTEM AVAILABILITY

Except Export
- The ATC system is a Three-Zone Air Conditioning System.

Export
- Two different types of systems are currently available for these vehicles.
> Dual-Zone Air Conditioning System for all vehicles with 2.4L and 2.5L engines and all SWB vehicles with 3.3L engines.
> Three-Zone Air Conditioning System for all LWB vehicles.

CABIN HEATER, EXPORT WITH DIESEL ENGINE
A Cabin Heater is used in conjunction with the ATC system. The Cabin Heater is designed to supply the vehicle's occupants with heat prior to the engine reaching operating temperature. For additional information on this system, refer to Cabin Heater under General Information and Diagnostic Procedures in this manual.

SYSTEM CONTROLS

The ATC Module:
- is fully addressable with the DRBIII(R).
- communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
- provides an A/C request over the PCI Bus to the Powertrain Control Module (PCM) when compressor operation is desired.
- for exports with diesel engines, provides a Cabin Heater activation request over the PCI Bus to the Front Control Module (FCM) when conditions are favorable for Cabin Heater operation.
- uses input from the evaporator temperature sensor to present evaporator freeze up while maintaining optimum cooling performance.
- uses input from infrared (I/R) sensors, which measure surface temperature, to maintain occupant comfort levels.
> The I/R sensors are mounted in the instrument panel center bezel.
- can be operated in a manual mode.
- provides a blower relay on request over the PCI Bus to the Front Control Module (FCM) when blower operation is desired.
- controls front blower operating speed, providing 10 speeds in manual mode and infinite speeds in automatic mode.
- controls rear blower operating speed, providing 10 speeds in manual mode and infinite speeds in automatic mode.
> The separate front and rear Blower Motor Controllers operate as follows: When blower operation is desired, the Blower Motor Controller provides a 10.0 volt signal to the ATC Module over a control circuit. The ATC Module provides a variable duty cycle ground to the 10.0 volt signal based on input from the blower switch. When the blower switch is set to LO speed, the ATC Module provides a short duty cycle (less time grounding the signal voltage). As higher blower speeds are requested, the ATC Module increases the duty cycle (more time grounding the signal voltage). When the blower switch reaches HI speed, the duty cycle increases to where the signal pattern is almost a flat line (with brief voltage spikes).
- controls the front and rear electronic door actuators' operation.
> A simplified control system for operation of the mode, recirculation, and temperature control actuators provides positive positioning without the complexity of feedback from position sensors. The ATC Module knows the number of operating actuator revolutions required for full door travel as well as the number of actuator commutator pulses per revolution. Using these parameters, the ATC Module runs the actuator for the number of commutator pulses that correspond to the desired door position. To maintain accuracy, the system recalibrates itself periodically at known zero and full travel conditions.
- activates and deactivates the Rear ATC Switch.

The Rear ATC Switch (Three-Zone Only):
- provides desired rear blower speed input to the ATC Module.
- provides desired rear blend and mode door position input to the ATC Module.

The Dual-Zone ATC system uses:
- two front, two-wire electronic blend door actuators.
- one front, two-wire electronic mode door actuator.
- one, two-wire electronic recirculation door actuator.

The Three-Zone ATC system uses:
- two front, two-wire electronic blend door actuators.
- one front, two-wire electronic mode door actuator.
- one, two-wire electronic recirculation door actuator.
- one rear, two-wire electronic blend door actuator.
- one rear, two-wire electronic mode door actuator.

System Relays
- The Integrated Power Module (IPM) houses and provides power to the A/C Clutch Relay, Front Blower Motor Relay, and Rear Blower Motor Relay.

SYSTEM REVISIONS

Revisions to the 2003 ATC system include:
- all new version 13 (Two-Zone) and OF (Three- Zone) system software.

CAUTION: Automatic Temperature Control (ATC) Modules with software versions 41 and 0A used in 2001 and 2002 RS/RG vehicles are NOT compatible with software versions 13 and OF used in 2003 RS/RG vehicles. Do NOT install an ATC Module with software version 41 or 0A in a 2003 RS/RG vehicle or an ATC Module with software version 13 or 0F in a 2001 or 2002 RS/RG vehicle. Use the DRBIII(R) to verify which version software the ATC Module is using by selecting Body Systems, Automatic Temperature Control, and then selecting Module Display.

- a Two-Zone HVAC system on select models.
- a Cabin Heater used in conjunction with the ATC system. For additional information on this system, refer to The AC Cooldown Test, under System Diagnostics in this General Information section, and refer to Cabin Heater under General Information and Diagnostic Procedures.
- deletion of the rear IR sensor.

SYSTEM DIAGNOSTICS
Fault detection is through active and stored Diagnostic Trouble Codes (DTCs)
- DTCs are displayed by the DRBIII(R).
- Active DTCs are those which currently exist in the system. The condition causing the fault must be repaired in order to clear this type of DTC.
- Stored DTCs are those which occurred in the system since the ATC Module received the last "clear diagnostic info" message.

The AC Cooldown Test:
- is actuated with the DRBIII(R).
- checks A/C system performance based on evaporator temperature sensor input.
- forces the ATC to initiate the Cabin Heater Activation request when the vehicle is equipped with a Diesel Cabin Heater Assist.

WARNING: DO NOT OPERATE THE DCHA IN AN ENCLOSED AREA SUCH AS A GARAGE THAT DOES NOT HAVE EXHAUST VENTILATION FACILITIES. ALWAYS VENT THE DCHA's EXHAUST WHEN OPERATING THE DCHA. REFER TO VENTING THE DCHA's EXHAUST UNDER CABIN HEATER IN THE GENERAL INFORMATION PORTION OF THIS SECTION FOR PROPER EXHAUST VENTING INSTRUCTIONS. FAILURE TO FOLLOW THESE INSTRUCTIONS MAY RESULT IN PERSONAL INJURY OR DEATH.

CAUTION: Do not activate the A/C Cooldown Test with the engine off. Failure to follow these instructions may result in internal damage to the DCHA Heater Module.

> The FCM monitors the PCI bus for the Cabin Heater Activation request. The request carries the status bit that the FCM requires to activate its' Cabin Heater Assist Control output. This output is a low side driver (coming from FCM pin 15) which supplies a ground signal to the Cabin Heater (pin 5). When the Cabin Heater receives this ground signal input, it interprets this as an activation signal.
> The FCM low side driver is also capable of diagnostic sensing. The driver will sense an open circuit when the driver is off, and will sense a short to voltage when the driver is on. The FCM will set DTCs for both of these types of faults. For additional information, refer to Cabin Heater under General Information and Diagnostic Procedures in the manual.
> Will not run the air conditioning portion of this test if ambient temperature is below 12°C (53°F).
> The forced Cabin Heater activation will occur even if the air conditioning portion of this test fails to initiate because AC Cooldown test criteria was not met. When activated, the DCHA will operate for approximately seven minutes. Three minutes to run and four minutes to purge.
> will pass the air conditioning portion of this test if the evaporator temperature drops 6.7°C (20°F) within two minutes of starting this test.
> messages (air conditioning related only) display on the DRBIII(R) after running this test.
> These messages will clear after paging back out of this test. Therefore, it is important to note all of the AC Cooldown test messages before doing so.
> All Cabin Heater-related DTCs display under Cabin Heater, Read DTCs.
> will cause the DELAY and Snowflake VF segments on the ATC to flash for 162 seconds (RG with DCHA only). If the air conditioning portion of this test fails, the DELAY and Snowflake VF segments will continue to flash until the vehicle is driven more than three miles.
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