Heating & A/C System

HEATING AND A/C SYSTEM

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

SYSTEM CONTROLS

MANUAL TEMPERATURE CONTROL (MTC)
The Manual Temperature Control (MTC):
- controls blower motor operation, providing four blower speeds (Low, M1, M2, & High).
- interfaces with the BCM through hardwired circuits .
- provides temperature setting information to the BCM through a resistor.
- provides an A/C request, an EBL request, and mode switch setting information to the BCM through a resistive multiplexed circuit.
The Body Control Module (BCM):
- drives the EBL status indicator in the MTC. Refer to additional information about rear window defogger operation.
- drives the electric door actuators (mode, blend, recirc).
- sends and A/C request, over the PCI Bus, to the PCM when A/C operation is desired.
- uses Evaporator Temperature Sensor data to prevent evaporator freeze up while maintaining optimum cooling performance.
The MTC HVAC system uses:
- one, five-wire electric blend door actuator.
- one, five-wire electric mode door actuator.
- one, two-wire electric recirculation door actuator.

AUTOMATIC TEMPERATURE CONTROL (ATC)
The Automatic Temperature Control (ATC):
- is addressable with the DRBIII(R)
- communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
- can be operated in a manual mode.
- uses an integral-mounted aspirator motor and in-car temperature sensor to maintain occupant comfort levels when set in an automatic mode.
- provides a request over the PCI Bus to the BCM when door actuator (blend, mode, recirculation) operation is desired.
- provides a request over the PCI Bus to the BCM when A/C operation is desired.
- provides a request over the PCI Bus to the BCM when EBL operation is desired.
- provides desired blower motor operating speed data over the PCI Bus to the BCM.
The Body Control Module (BCM):
- drives the ATC status indicators (EBL, A/C, and Recirc) over the PCI Bus.
- remembers the last temperature setting at power down.
- sets the initial temperature setting via the PCI Bus when the ATC is powered up.
- drives the electric door actuators (mode, blend, recirculation).
- controls blower motor operating speed.
- There are 14 blower speeds when the ATC is in manual mode and infinite speeds when the ATC is in automatic mode.
- sends a request over the PCI Bus to the PCM when A/C operation is desired.
- uses sun load sensor data to maintain occupant comfort levels when the ATC is set in an automatic mode.
- uses Evaporator Temperature Sensor data to prevent evaporator freeze up while maintaining optimum cooling performance.
Blower Motor Operation
- The Blower Power Module provides the blower motor with power and a path to ground. It also sends a blower control signal to the BCM. The BCM constantly receives desired blower speed data from the ATC over the PCI Bus. Using this data, the BCM processes the blower control signal which sets the speed that the Blower Power Module will run the blower motor.
The ATC HVAC system uses:
- one, five-wire electric blend door actuator
- one, five-wire electric mode door actuator
- one, two-wire electric recirculation door actuator.

SYSTEM REVISIONS (ATC & MTC)
- The 2005 JR Manual Temperature Control (MTC) HVAC system remains carryover from 2004.
- The Automatic Temperature Control (ATC) HVAC system is new for 2005 JR. The ATC system is similar to that used in LH vehicles.

SYSTEM DIAGNOSTICS (ATC & MTC)
Fault detection is through stored Diagnostic Trouble Codes (DTC's)
- DTC's are displayed by the DRBIII(R)
- All ATC and MTC DTC's are stored in the BCM. Diagnostics for these DTC's can be found in the Heating & A/C category of this manual.
- DTC's pertaining to A/C compressor control circuits and the radiator fan control circuits are stored in the PCM. Diagnostics for these DTC's can be found in the Powertrain Diagnostic Procedures manual. Diagnostics for symptoms pertaining to A/C compressor operation can also be found in the Powertrain Diagnostics Procedures manual.

FOLLOWING A REPAIR (ATC & MTC)
Calibrate HVAC Door Actuators
- The electric door actuators (blend, mode, recirculation) must be calibrated after making any repairs to the HVAC system.
- To calibrate the door actuators, either disconnect the battery or remove JB Fuse #5 for five minutes, or using the DRBIII(R), select Body, Body Computer, Miscellaneous, and Calibrate HVAC Door Motors.