Operation

HEATING AND A/C SYSTEM

AUTOMATIC TEMPERATURE CONTROL (ATC)

MODULE USAGE

CAUTION: Do not swap ATC Modules from vehicle to vehicle. Software versions differ between models and between model years. Installing a ATC Module with software that is incompatible for a given vehicle can result in either improper or failed HVAC system operation.

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 except LWB vehicles.
- 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 prevent 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.
- provides a cold engine blower lockout function.
- A Blower Speed Clamping feature minimizes occupant discomfort by controlling the amount of warm air coming out of the HVAC system should the Powertrain Control Module (PCM) disable A/C Compressor operation while the Automatic Temperature Control (ATC) is set in an automatic mode. The PCM disables the A/C compressor if the A/C pressure is too low, if the A/C pressure is too high, if engine overheating is immanent, or if an engine overheating condition exists. The ATC clamps the blower speed if the outside air temperature is greater than50° F (10° C) and the PCM has disabled the A/C compressor. This means that the ATC will not adjust blower speed automatically when the clamping feature is enabled, e.g. if the clamping feature is enabled while in Auto Lo the blower will continue to run in low speed; if the clamping feature is enabled while in Auto Lo and the operator selects Auto Hi the blower will continue to run in low speed; if the clamping feature is enabled while in Auto Hi the blower will continue to run at the highest speed. In any case the operator can manually change the blower speed as desired. When diagnosing blower related symptoms verify that none of the above conditions for disabling the A/C compressor exist before diagnosing the blower circuits and components.

- 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 electric 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 electric blend door actuators.
- one front, two-wire electric mode door actuator.
- one, two-wire electric recirculation door actuator.

The Three-Zone ATC system uses:
- two front, two-wire electric blend door actuators.
- one front, two-wire electric mode door actuator.
- one, two-wire electric recirculation door actuator.
- one rear, two-wire electric blend door actuator.
- one rear, two-wire electric 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
The 2006 ATC system remains mostly carryover from 2005.

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 dear 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 CAN RESULT IN PERSONAL INJURY OR DEATH.

CAUTION: Do not activate the A/C Cooldown Test with the engine off. Failure to follow these instructions can 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.

MANUAL TEMPERATURE CONTROL (MTC)

MODULE USAGE

CAUTION: Do not swap MTC modules from vehicle to vehicle. Software versions differ between models and between model years. Installing a MTC module with software that is incompatible for a given model year can result in either improper or failed HVAC system operation.

SYSTEM AVAILABILITY

EXCEPT EXPORT
- Three different types of systems are currently available for these vehicles.
- Single-Zone Air Conditioning System
- Dual-Zone Air Conditioning System
- Three-Zone Air Conditioning System

EXPORT
- Two different types of systems are currently available for these vehicles.
- Single-Zone Air Conditioning System
- Dual-Zone Air Conditioning System

CABIN HEATER, EXPORT WITH DIESEL ENGINE
- A Cabin Heater is used in conjunction with the HVAC 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 A/C-Heater Control Module:
- is fully addressable with the DRBIII(R).
- communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
- provides an A/C request to the Powertrain Control Module (PCM) over the PCI Bus when compressor operation is desired.
- uses input from the evaporator temperature sensor to prevent evaporator freeze up while maintaining optimum cooling performance.
- for exports with diesel engines, provides a Cabin Heater activation request to the Front Control Module (FCM) over the PCI Bus when conditions are favorable for Cabin Heater operation.
- for RS vehicles, provides a blower relay on request to the FCM over the PCI Bus upon ignition on.
- for RG vehicles, provides a blower relay on request to the FCM over the PCI Bus when the Power switch on the A/C-Heater Control Module is turned on.
- controls front blower operating speed. For RS vehicles, the four speed settings are Low, M1, M2, and High. For RG vehicles the five speed settings are Low, M1, M2, M3, and High.
- for RS vehicles uses the blower switch to control system on/off and blower speed.
- for RG vehicles uses the power switch to control system on/off and the blower switch to control blower speed.
- for RS vehicles uses the rear wiper/washer switch to control rear wiper/washer operation.
- for RS vehicles, provides a rear wiper on request to the Body Control Module (BCM) when rear wiper operation is desired.
- for RS vehicles, provides a rear washer on request to the Body Control Module (BCM) when rear washer operation is desired.
- controls EBL operation.
- on three-zone systems, activates and deactivates the Rear A/C-Heater Control.
- on three-zone systems, controls rear blower operating speed. The three speed settings are Low, Med, and High.
- controls the front and the three-zone system rear electric 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 A/C- Heater Control 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 A/C - Heater Control 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.

On Three-Zone systems, the Rear A/C-Heater Control:
- controls rear blower motor operating speed. The three blower speeds are Low, Med, and High.
- provides desired rear blend and mode door position input to the A/C-Heater Control Module.

The Single-Zone HVAC system uses:
- one, two-wire electric blend door actuator.
- one, two-wire electric mode door actuator.
- one, two-wire electric recirculation door actuator.

The Dual-Zone HVAC system uses:
- two, two-wire electric blend door actuators.
- one, two-wire electric mode door actuator.
- one, two-wire electric recirculation door actuator.

The Three-Zone HVAC system uses:
- two front, two-wire electric blend door actuators.
- one front, two-wire electric mode door actuator.
- one, two-wire electric recirculation door actuator.
- one rear, two-wire electric blend door actuator.
- one rear, two-wire electric 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
The 2006 MTC system remains mostly carryover from 2005.

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 A/C-Heater Control Module received the last "clear diagnostic info" message.

The A/C Cool down Test:
- is actuated with the DRBIII(R).
- checks A/C system performance based on evaporator temperature sensor input.
- will not run if ambient temperature is below 12.7° C (55° F).
- will pass if the evaporator temperature drops 6.7° C (20° F) within two minutes of starting the test.
- faults display on the DRBIII(R) as test messages only after running the test.
- faults will not display on the DRBIII(R) as Diagnostic Trouble Codes.
- for RS vehicles will cause the Rear Wipe/Wash and A/C status indicators on the A/C-Heater Control Module to flash alternately while the test is running.
- for RG vehicles will cause the PWR and A/C status indicators on the A/C
- Heater Control Module to flash alternately while the test is running.
- The A/C status indicator will flash twice per second to indicate that the A/C Cooldown Test needs to be run. The A/C status indicator will stop flashing twice per second if either the A/C Cooldown Test returns passed, or if any button on the control is pressed, or if the ignition is cycled and the odometer shows greater than eight miles.

The HVAC Door Recalibration function:
- is actuated with the DRBIII(R).
- After completing HVAC Door Recalibration, the DRBIII(R) will the store the total span and the status of each door actuator. Selecting HVAC Door Cal Monitor in the System Tests will display this information.

- homes and repositions door actuators.
- monitors for door span faults on the actuator circuits.
- faults display on the DRBIII(R) as test messages only after running the test.
- faults will not display on the DRBIII(R) as Diagnostic Trouble Codes.
- for RS vehicles will cause the Rear Wipe/Wash and RECIRC status indicators on the A/C-Heater Control Module to flash alternately while the test is running.
- for RG vehicles will cause the PWR and RECIRC status indicators on the A/C - Heater Control Module to flash alternately while the test is running.
- The RECIRC status indicator will flash twice per second to indicate that the HVAC Door Recalibration Test needs to be run. The RECIRC status indicator will stop flashing twice per second if either the HVAC Door Recalibration Test returns passed, or if any button on the control is pressed, or if the ignition is cycled and the odometer shows greater than eight miles.

The Actuator Circuit Test:
- is actuated with the DRBIII(R).
- monitors for shorted actuator circuits.
- allows service to easily diagnose and troubleshoot up to three simultaneous shorts.
- supplements the continuous diagnostics on the actuator drive system.
- faults display on the DRBIII(R) as test messages only after running the test.
- faults will not display on the DRBIII(R) as Diagnostic Trouble Codes.

When Performing the Actuator Circuit Test

CAUTION:
- Shorted rear door driver circuits can cause additional Actuator Circuit Test messages to set for circuits where no condition exists to cause a fault.
- To ensure a proper diagnosis, repair all Short Too Complex messages first, all rear door driver circuit related messages second, all common door driver circuit related messages third, and all front door driver circuit related messages last.
- The DRBIII(R) can display up to three Actuator Circuit Test messages at a time. After repairing each Actuator Circuit Test message, cycle the ignition switch, then rerun the Actuator Circuit Test to ensure no new messages exist.

- The Short Too Complex message:
- indicates that a specific determination of which lines are shorted could not be made.
- is caused by more than three drivers being shorted in the same direction. For example, four drivers all shorted to ground, or two or more drivers shorted with at least one driver shorted to ignition/battery and one driver shorted to ground.

- Messages displaying:
- XXX Driver/Circuit Shorted to Ignition/ Battery will set on a per-driver basis.
- XXX Driver/Circuit Shorted to Ground will set on a per-driver basis.
- the same two drivers/circuits shorted to ignition/battery as-well-as shorted to ground indicates that two actuator driver circuits are shorted together.

- When the test returns passed, then troubleshooting should proceed to clearing faults and running the HVAC Door Recalibration system test as a final check of system health.