Pinpoint Test M: The Air Conditioning (A/C) Is Always On - A/C Compressor Does Not Cycle
Climate Control System
Pinpoint Tests
Pinpoint Test M: The Air Conditioning (A/C) is Always On - A/C Compressor Does Not Cycle
Refer to Wiring Diagram Set 54, Manual Climate Control System for schematic and connector information. Diagrams By Number
Refer to Wiring Diagram Set 55, Automatic Climate Control System for schematic and connector information. Diagrams By Number
Normal Operation
Under normal operation, when A/C button is pressed, a message is sent from the Front Controls Interface Module (FCIM) module over the Medium Speed Controller Area Network (MS-CAN) bus to the HVAC module. The HVAC module then sends an A/C request message over the MS-CAN bus to the PCM. If the vehicle is equipped with next generation navigation, when MAX A/C is selected on the touch screen, the Audio Control Module (ACM) sends a message is over the MS-CAN bus to the HVAC module that MAX A/C has been selected. Ignition voltage is provided to the A/C clutch relay switch through circuit SBB24 (VT/RD). When the PCM energizes the relay, ignition voltage is supplied to the A/C clutch through circuit CH401 (VT/WH). Ground is supplied for the A/C clutch through circuit GD120 (BK/GN).
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- PCM
- A/C evaporator discharge temperature sensor
- A/C control relay
- A/C clutch air gap
PINPOINT TEST M: THE AIR CONDITIONING (A/C) IS ALWAYS ON - A/C COMPRESSOR DOES NOT CYCLE
NOTE: Before carrying out the following test, diagnose any PCM or instrument cluster DTCs.
NOTE: When disconnecting and reconnecting the pressure transducer electrical connector, make sure that the connector-locking device is in place and that the locking device and connector are correctly and fully seated.
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M1 CHECK THE A/C EVAPORATOR TEMPERATURE (EVAP_TEMP) HVAC PID
- Ignition ON.
- Allow the vehicle exterior and interior to stabilize to an ambient temperature above 16°C (60°F).
- Enter the following diagnostic mode on the scan tool: EVAP_TEMP HVAC PID.
- Does the EVAP_TEMP HVAC PID read similar to the ambient temperature?
Yes
GO to M2.
No
INSTALL a new A/C evaporator discharge temperature sensor. TEST the system for normal operation.
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M2 CHECK THE AIR CONDITIONING CLUTCH (WAC/ACCR) PCM PID WITH THE A/C OFF
- Enter the following diagnostic mode on the scan tool: WAC/ACCR PCM PID.
- Does the WAC/ACCR PCM PID read ON?
Yes
GO to M5.
No
GO to M3.
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M3 CHECK FOR VOLTAGE TO THE A/C COMPRESSOR CLUTCH FIELD COIL
- Ignition OFF.
- Disconnect: A/C Compressor Clutch Field Coil C100.
- Ignition ON.
- Select the OFF position on the HVAC module.
- With the engine running, measure the voltage between A/C compressor clutch field coil C100-1, circuit CH401 (VT/WH), harness side and ground.
- Is any voltage present?
Yes
GO to M4.
No
ADJUST the A/C compressor clutch gap. REFER to Air Conditioning (A/C) Clutch Air Gap Adjustment Adjustments. TEST the system for normal operation.
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M4 CHECK CIRCUIT CH401 (VT/WH) FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: A/C Clutch Relay.
- Ignition ON.
- Measure the voltage between A/C compressor clutch field coil C100-1, circuit CH401 (VT/WH), harness side and ground.
- Is any voltage present?
Yes
REPAIR circuit CH401 (VT/WH) for a short to voltage. TEST the system for normal operation.
No
INSTALL a new A/C clutch relay. TEST the system for normal operation.
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M5 CHECK THE PCM CONNECTION
- Clear the DTCs.
- Disconnect all of the PCM connectors.
- Check for:
- corrosion.
- pushed-out connectors.
- incorrectly seated connector.
- Connect and correctly seat all of the PCM connectors.
- Operate the system.
- Does the concern return?
Yes
INSTALL a new PCM. TEST the system for normal operation.
No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.
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