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Pinpoint Test P: The Air Conditioning (A/C) is Always On - A/C Compressor Does Not Cycle




Climate Control System

Pinpoint Tests

Pinpoint Test P: 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

For vehicles equipped with navigation, when A/C button is pressed, a message is sent from the Front Controls Interface Module (FCIM) 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 Body Control Module (BCM), then from the BCM through the High Speed Controller Area Network (HS-CAN) bus to the PCM. When MAX A/C is selected on the touch screen, the Front Display Interface Module (FDIM) sends a message over the MS-CAN bus to the HVAC module that MAX A/C has been selected.

For vehicles not equipped with navigation, when A/C is requested, a message is sent from the HVAC module over the MS-CAN bus to the BCM, then from the BCM through the HS-CAN bus to the PCM.

Voltage is provided to the A/C clutch relay coil from Battery Junction Box (BJB) fuse 77 (10A) and switch contacts from Battery Junction Box (BJB) fuse 30 (10A). When A/C is requested and A/C line pressures allow, a ground is provided to the A/C clutch relay coil from the PCM, energizing the A/C clutch relay. When the PCM energizes the relay, voltage is supplied to the A/C compressor clutch field coil from the relay. Ground is supplied for the A/C compressor clutch field coil.

The evaporator temperature sensor is used for A/C compressor cycling. An accurate evaporator temperature is critical for compressor engagement. The PCM uses the temperature measurement to turn the A/C compressor off before the evaporator temperatures are cold enough to freeze the condensation on the evaporator core.

This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- PCM
- Evaporator temperature sensor
- A/C clutch relay
- A/C compressor clutch air gap

PINPOINT TEST P: THE AIR CONDITIONING (A/C) IS ALWAYS ON - A/C COMPRESSOR DOES NOT CYCLE

NOTE: Before carrying out the following test, diagnose any HVAC or PCM or DTCs.

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P1 CHECK THE A/C EVAPORATOR TEMPERATURE (EVAP_TEMP) HVAC PID

- Ignition ON.
- Allow the vehicle exterior and interior to stabilize to the ambient temperature.
- Enter the following diagnostic mode on the scan tool: HVAC DataLogger.
- Monitor the EVAP_TEMP HVAC PID
- Does the EVAP_TEMP HVAC PID read similar to the ambient temperature?

Yes
GO to P2.

No
INSTALL a new heater core and evaporator core housing. REFER to Climate Control Service and Repair. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.

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P2 CHECK THE AIR CONDITIONING COMPRESSOR COMMANDED STATE (ACC_CMD) PCM PID WITH THE A/C OFF

- Enter the following diagnostic mode on the scan tool: PCM DataLogger .
- Monitor the ACC_CMD PCM PID
- Select PANEL press the A/C button (indicator off) on the HVAC controls.
- Does the ACC_CMD PCM PID read OFF?

Yes
GO to P3.

No
GO to P7.

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P3 CHECK THE A/C COMPRESSOR CLUTCH ENGAGEMENT WITH RELAY DISCONNECTED

- Ignition OFF.
- Disconnect: A/C Clutch Relay.
- Start the engine.
- With the engine running, observe the A/C compressor clutch.
- Is the compressor clutch disengaged?

Yes
GO to P4.

No
GO to P6.

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P4 CHECK THE A/C CLUTCH RELAY

- Select PANEL and press the A/C button (indicator off) on the HVAC controls.
- With the engine running, connect a 12-volt test light between A/C clutch relay socket, circuit CBB77 (WH) and A/C clutch relay socket, circuit CH302 (WH/BN).




- Does the test light illuminate?

Yes
GO to P5.

No
INSTALL a new A/C clutch relay. TEST the system for normal operation.

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P5 CHECK THE A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR A SHORT TO GROUND

- Ignition OFF.
- Disconnect: PCM C1381B (5.0L, 6.2L).
- Disconnect: PCM C175B (3.7L).
- Disconnect: PCM C1551B (3.5L).

For 3.7L, 5.0L and 6.2L




- Measure the resistance between ground and:
- For 3.7L, PCM C175B-12, circuit CH302 (WH/BN), harness side.
- For 5.0L and 6.2L, PCM C1381B-12, circuit CH302 (WH/BN), harness side.

For 3.5L




- For 3.5L, measure the resistance between ground and PCM C1551B-2, circuit CH302 (WH/BN), harness side.
- Is the resistance greater than 10,000 ohms?

Yes
GO to P7.

No
REPAIR circuit CH302 (WH/BN) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.

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P6 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.
- 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
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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P7 CHECK THE PCM CONNECTION

- Disconnect all the PCM connectors.
- Inspect the PCM connectors for:
- corrosion
- pushed-out terminals
- damaged terminals
- Connect and correctly seat all the PCM connectors.
- Clear the DTCs.
- Enter the following diagnostic mode on the scan tool: Self-Test - PCM.
- Operate the system and verify the concern is still present.
- Is the concern still present?

Yes
INSTALL a new PCM. REFER to Electronic Engine Controls Service and Repair. 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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