Heating & A/C System

CAUTION: Do not remove the A/C-Heater Control Module from one vehicle and install it in another vehicle. The module's software configures differently for JTEC and NGC, and for vehicles with and without a CMTC. Failure to follow these instructions can either cause CMTC display problems or an inaccurate temperature to display. It can also cause an ambient temperature sensor open DTC to set when support should not be operative or it can completely prevent the A/C-Heater Control Module from reporting ambient temperature sensor circuit DTCs.

SYSTEM AVAILABILITY
- A Single-Zone HVAC system is available in these vehicles.

SYSTEM CONTROLS
The Heater Control Module:
- is fully addressable with the DRBIII(R).
- communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
- controls blower motor operation, providing four blower speeds (Low, M1, M2, & High).
- controls heated mirror operation (if equipped).
- controls electronic door actuator operation.

The A/C-Heater Control Module:
- is fully addressable with the DRBIII(R).
- 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 (if equipped).
- controls electronic door actuator operation.

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

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.

SYSTEM REVISIONS
The 2004 AN and AN84 HVAC system remains mostly carryover from 2003.

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 Cooldown Test:
- is actuated with the DRBIII(R).
- checks A/C system performance based on evaporator temperature sensor input.
- will fail if evaporator temperature is below 18.3°C (65°F) when initiating the test.
- will pass if the evaporator temperature drops 6.7°C (20°F).
- 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.
- 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 either the test returns passed or the ignition key is cycled. It will also prevent the EBL mode switch status indicator (if equipped) from indicating EBL operating status. However, the EBL mode switch will continue to function in this state.

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:
- 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 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.