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System Operation

HEATING & A/C SYSTEM

SYSTEM AVAILABILITY
Depending on the model, either a Single-Zone Air Conditioning System or Dual-Zone Air Conditioning System is available in these vehicles.

SYSTEM CONTROLS

The A/C-Heater Control Module:
* is fully addressable with the DRB III.
* communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
* uses input from the evaporator temperature sensor to prevent evaporator freeze up while maintaining optimum cooling performance.
* provides an A/C request to the Powertrain Control Module (PCM) over the PCI Bus when compressor operation is desired.
* controls blower motor operation, providing four blower speeds (Low, M1, M2, & High).
* controls heated mirror operation.
* controls electronic door actuator 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.

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

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

System Diagnostics
- Fault detection is through active and stored Diagnostic Trouble Codes (DTC's)
- DTC's are displayed by the DRB III.

Active DTC's 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 DTC's are those which occurred in the system since the A/C-Heater Control Module received the last "clear diagnostic info" message.


The A/C Cooldown Test:
* Is actuated with the DRB III.
* 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 DRB III as test messages only after running the test.
* faults will not display on the DRB III as Diagnostic Trouble Codes.
* will cause the A/C mode switch status indicator to flash while the test is running.

If the test fails, the status indicator will continue to flash until the test returns passed. It will also prevent the EBL mode switch status indicator from indicating EBL operating status. However, the EBL mode switch will continue to function in this state.

The EVAC Door Recalibration function:
* is actuated with the DRB III.
* monitors for faults on the actuator circuits.
* faults display on the DRB III as test messages only after running the test.
* faults will not display on the DRB III as Diagnostic Trouble Codes.
* will cause the EBL mode switch status indicator to flash while the test is running.

If the test fails, the status indicator will continue to flash until the test returns passed. It will also prevent the A/C mode switch status indicator from indicating A/C operating status. However, the A/C mode switch will continue to function in this state.

The Actuator Circuit Test:
* is actuated with the DRB III.
* monitors for faults on the 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 DRB III as test messages only after running the test.
* faults will not display on the DRB III as Diagnostic Trouble Codes.

When Performing The Actuator Circuit Test:

CAUTION:
- Shorted common 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 common door driver circuit related messages second, and all other door driver circuit related messages last.
- The DRB III 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.

After the Actuator Circuit Test is run on systems with less than six actuators, the actuator drive system is left in a state where further actuator positioning requests are ignored from both the panel and the DRB III. This state is cleared by cycling the ignition switch (cycling power to the control).

If 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.