Heater and Air Conditioning

HEATING & AIR CONDITIONING

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 DRB III.
- 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 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 (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 2003 AN and AN84 HVAC system remains mostly carryover from 2002. Revisions to the 2003 HVAC system include:
- a change in A/C mode switch status indicator operation when performing the A/C Cool down test. Refer to The A/C Cool-down Test under System Diagnostics for more information.
- a change in EBL mode switch status indicator operation when performing the HVAC Door Recalibration. Refer to the HVAC Door Recalibration Function under System Diagnostics for more information.
- updated diagnostic procedures using span data to diagnose HVAC Door Recalibration fault messages.

COOLING SYSTEM REQUIREMENTS
To maintain the performance level of the HVAC system, the engine cooling system must be properly maintained. The use of a bug screen is not recommended. Any obstructions in front of the radiator or condenser will reduce the performance of the air conditioning and engine cooling systems.

The engine cooling system includes the heater core and the heater hoses. Refer to Cooling for more information before the opening of, or attempting any service to the engine cooling system.

REFRIGERANT SYSTEM SERVICE PORTS
The two refrigerant system service ports are used to charge, recover/recycle, evacuate, and test the air conditioning refrigerant system. Unique service port coupler sizes are used on the R-134a system, to ensure that the refrigerant system is not accidentally contaminated by the use of the wrong refrigerant (R-12), or refrigerant system service equipment.

The high pressure service port is located on the liquid line between the condenser and the evaporator, near the front of the engine compartment. The low pressure service port is located on the compressor manifold, directly over the suction port of the compressor, for 5.9L Engine. It is on the suction line between the compressor and the evaporator for the 4.7L engine.

Each of the service ports has a threaded plastic protective cap installed over it from the factory. After servicing the refrigerant system, always reinstall both of the service port caps.