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Manual Temperature Control (MTC)

MANUAL TEMPERATURE CONTROL (MTC)

CAUTION: Manual Temperature Control (MTC) Modules with software versions 0614 and 0700 used in 2001 and 2002 RS/RG vehicles are NOT compatible with software version 0802 used in 2003 RS/RG vehicles. Do NOT install an MTC Module with software version 0614 or 0700 in a 2003 RS/RG vehicle. Use the DRBIII(R) to verify which version software the MTC Module is using by selecting Body Systems, HVAC, and then selecting Module Display.

SYSTEM AVAILABILITY

Except Export
- Three different types of systems are currently available for these vehicles.
- Single-Zone Air Conditioning System
- Dual-Zone Air Conditioning System
- Three-Zone Air Conditioning System

Export
- Two different types of systems are currently available for these vehicles.
- Single-Zone Air Conditioning System
- Dual-Zone Air Conditioning System

CABIN HEATER (EXPORT WITH DIESEL ENGINE)
A Cabin Heater is used in conjunction with the HVAC system. The Cabin Heater is designed to supply the vehicle's occupants with heat prior to the engine reaching operating temperature. For additional information on this system, refer to Cabin Heater under General Information and Diagnostic Procedures in this manual.

SYSTEM CONTROLS

The A/C-Heater Control Module:
- is fully addressable with the DRBIII(R).
- communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
- provides an A/C request to the Powertrain Control Module (PCM) over the PCI Bus when compressor operation is desired.
- uses input from the evaporator temperature sensor to prevent evaporator freeze up while maintaining optimum cooling performance.
- for experts with diesel engines, provides a Cabin Heater activation request to the Front Control Module (FCM) over the PCI Bus when conditions are favorable for Cabin Heater operation.
- provides a blower relay on request to the Front Control Module (FCM) over the PCI Bus when blower operation is desired.
- controls front blower operating speed. The five speed settings are Low, M1, M2, M3, and High.
- controls EBL operation.
- on three-zone systems, activates and deactivates the Rear A/C-Heater Control.
- on three-zone systems, controls rear blower operating speed. The three speed settings are Low, Med, and High.
- controls the front and the three-zone system rear electronic door actuators' 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.

On Three-Zone systems, the Rear A/C-Heater Control:
- controls rear blower motor operating speed. The three blower speeds are Low, Med, and High.
- provides desired rear blend and mode door position input to the A/C-Heater Control Module.

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.

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

The Three-Zone HVAC system uses:
- two front, two-wire electronic blend door actuators.
- one front, two-wire electronic mode door actuator.
- one, two-wire electronic recirculation door actuator.
- one rear, two-wire electronic blend door actuator.
- one rean two-wire electronic mode door actuator.

System Relays
- The Integrated Power Module (IPM) houses and provides power to the A/C Clutch Relay, Front Blower Motor Relay, and Rear Blower Motor Relay.

SYSTEM REVISIONS
Revisions to the 2003 MTC system include:
- all new version 0802 software.

CAUTION: Manual Temperature Control (MTC) Modules with software versions 0614 and 0700 used in 2001 and 2002 RS/RG vehicles are NOT compatible with software version 0802 used in 2003 RS/RG vehicles. Do NOT install an MTC Module with software version 0614 or 0700 in a 2003 RS/RG vehicle. Use the DRBIII(R) to verify which version software the MTC Module is using by selecting Body Systems, HVAC, and then selecting Module Display.

- an all-new System Test called the Actuator Circuit Test. Refer to The Actuator Circuit Test under System Diagnostics for more information.
- an updated HVAC Door Recalibration function that provides actuator span and status data to ease diagnosis of door span faults.
- updated diagnostic procedures using the actuator span status data to diagnose HVAC Door Recalibration Fault messages.

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 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 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 PWR and A/C status indicators on the A/C - Heater Control Module to flash alternately while the test is running.
- The A/C status indicator will flash twice per second to indicate that the A/C Cooldown Test needs to be run. The A/C status indicator will stop flashing twice per second if either the A/C Cooldown Test returns passed, or if any button on the control is pressed, or if the ignition is cycled and the odometer shows greater than eight miles.

The HVAC Door Recalibration Function
- is actuated with the DRBIII(R).
- After completing HVAC Door Recalibration, the DRBIII(R) will the store the total span and the status of each door actuator. Selecting HVAC Door Cal Monitor in the System Tests will display this information.
- homes and repositions door actuators.
- monitors for door span faults on the actuator circuits.
- 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 PWR and RECIRC status indicators on the A/C - Heater Control Module to flash alternately while the test is running.
- The RECIRC status indicator will flash twice per second to indicate that the HVAC Door Recalibration Test needs to be run. The RECIRC status indicator will stop flashing twice per second if either the HVAC Door Recalibration Test returns passed, or if any button on the control is pressed, or if the ignition is cycled and the odometer shows greater than eight miles.

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:
- Shorted rear 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 .E3hort Too Complex messages first, all rear door driver circuit related messages second, all common door driver circuit related messages third, and all front 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 closed 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.
- Message, 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.

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