Heating & A/C System

SYSTEM AVAILABILITY
- Depending on the model, either a Manual Temperature Control (MTC) or Automatic Zone Control (AZC) HVAC system is available in these vehicles.

SYSTEM CONTROLS
The Automatic Zone Control (AZC) Module:
- is fully addressable with the DRBIII(R).
- communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
- has dual infrared sensors, mounted in the AZC module face, which independently measure surface temperature to maintain occupant comfort levels.
- has dual-zone temperature-controls to provide a wide side-to-side variation in temperature to meet the needs of either front seat occupant.
- can be operated in a manual mode.
- uses engine temperature data, received over the PCI Bus, for cold engine blower lock-out.
- uses engine RPM data, received over the PCI Bus, for wide-open throttle A/C cut-out.
- uses vehicle speed data, received over the PCI Bus, to determine air-flow over the condenser for optimum cooling performance.
- uses Ambient Temperature Sensor data, received over the PCI Bus, to optimize comfort control.
- provides an A/C request to the BCM when compressor operation is desired.
- provides a request to the BCM when rear defogger operation is desired.
- controls fan speed, providing 10 blower speeds in manual mode and infinite speeds in automatic mode.
- The Blower Motor Controller provides a 5.0 volt signal to the AZC Module over the Blower Motor Control circuit. The AZC Module provides a variable duty cycle ground to the 5.0 volt signal based on input from the blower switch. When the blower switch is set to LO speed, the AZC Module provides a short duty cycle (less time grounding the signal voltage). As higher blower speeds are requested, the AZC 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 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 AZC 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 AZC 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 Body Control Module:
- uses Evaporator Temperature Sensor data to prevent evaporator freeze up while maintaining optimum cooling performance.
- controls rear defogger operation.

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

SYSTEM REVISIONS
The HVAC systems remain carryover from 2002. However, the 2003 and above model year AZC Module is NOT interchangeable with other model year AZC Modules due to revised control software.

SYSTEM DIAGNOSTICS (MTC)
Fault detection is through Diagnostic Trouble Codes (DTCs)

- DTCs are displayed by the DRBIII(R).
- DTCs pertaining to the Evaporator Temperature Sensor are stored in the BCM. Diagnostics for these DTCs can be found in the Heating & A/C category.
- Diagnostics for symptoms pertaining to A/C compressor operation can be found in the Heating & A/C category and in the Powertrain Diagnostic Procedures.
- DTCs pertaining to A/C compressor control circuits are stored in the PCM/ECM. Diagnostics for these DTCs can be found in the Powertrain Diagnostic Procedures.


SYSTEM DIAGNOSTICS (AZC)
Fault detection is through active and stored Diagnostic Trouble Codes (DTCs)
- DTCs are displayed by the DRBIII(R).

AZC Module DTCs
- 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.
- Active DTCs become stored DTCs when the condition that caused the active DTC no longer exists.
- Stored DTCs will be erased after 72 key cycles or by clearing them with the DRBIII(R).
- Diagnostics for symptoms pertaining to A/C compressor operation can be found in the Heating & A/C category and in the Powertrain Diagnostic Procedures.


BCM DTCs
- DTCs pertaining to the Evaporator Temperature Sensor are stored in the BCM. Diagnostics for these DTCs can be found in the Heating & A/C category.

PCM/ECM DTCs
- DTCs pertaining to A/C compressor control circuits are stored in the PCM/ECM. Diagnostics for these DTCs can be found in the Powertrain Diagnostic Procedures manual.

FOLLOWING A REPAIR (AZC)
Calibrate AZC Door Actuators
- Calibrate the door actuators after making any repairs to the AZC system. To calibrate the door actuators proceed as follows:
1. Turn the ignition on.
2. Set the AZC to automatic.
3. Turn the ignition off.
4. Remove the IOD fuse from the Power Distribution Center. Wait several seconds, and then install the IOD fuse.
5. Turn the ignition on. Do not touch any of the AZC controls for at least one minute to allow the calibration function to run to completion.