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




Climate Control System

Pinpoint Tests

Pinpoint Test G: 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

Normal Operation

Under normal operation, when A/C is requested, a ground signal is sent from the HVAC module to the Smart Junction Box (SJB) through circuit 1397 (GY/RD). The SJB then transmits an A/C request message through the High Speed Controller Area Network (HS-CAN) bus to the PCM.

4.0L only

Voltage is provided to the A/C cycling switch through circuit 391 (RD/YE). If the A/C cycling switch is closed (sufficient pressure) voltage is sent from the A/C cycling switch to the PCM (4.0L) through circuit 198 (DG/OG)/420 (DB/YE). When the PCM receives voltage from the pressure switch and the A/C pressure transducer does not indicate excessive pressure, the PCM provides a ground for the A/C clutch relay through circuit 321 (GY/WH).

4.6L and 5.4L only

Voltage is provided to the A/C cycling switch through circuit 391 (RD/YE). If the A/C cycling switch is closed (sufficient pressure) voltage is sent from the A/C cycling switch to the dual-function pressure switch (4.6L and 5.4L) through circuit 198 (DG/OG). If the dual-function pressure switch (4.6L and 5.4L) is closed (pressure not excessive), voltage is sent to the PCM through circuit 420 (DB/YE). When the PCM receives voltage from the pressure switches, the PCM provides a ground for the A/C clutch relay through circuit 321 (GY/WH).

When the relay is activated, ignition voltage is supplied to the A/C clutch solenoid through circuit 883 (PK/LB). Ground is supplied for the A/C clutch through circuit 1205 (BK).

- DTC B2175 A/C Request Signal Circuit Short to Ground - The module senses a continuous short to ground on the A/C request circuit.

This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- PCM
- SJB
- HVAC module
- A/C cycling switch
- A/C control relay
- A/C clutch air gap



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

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G1 CHECK THE AIR CONDITIONING REQUEST SIGNAL (AC_REQST) GEM PID


- Ignition ON.
- With the engine running, select the OFF position on the HVAC module.
- Enter the following diagnostic mode on the scan tool: AC_REQST Generic Electronic Module (GEM) PID.
- Does the AC_REQST GEM PID read OFF?

Yes
GO to G4.

No
GO to G2.

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G2 CHECK THE A/C SIGNAL WITH THE A/C OFF


- Ignition OFF.
- Disconnect: SJB C2280a.
- Disconnect: SJB C2280b.
- Ignition ON.
- With the engine running, select the OFF position on the HVAC module.
- Measure the voltage between SJB C2280b-29, circuit 1397 (GY/RD), harness side and SJB C2280a-36, circuit 1044 (WH/YE), harness side.




- Is the voltage greater than 10 volts?

Yes
GO to G3.

No
GO to G11.

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G3 CHECK CIRCUIT 1397 (GY/RD) FOR A SHORT TO GROUND


- Ignition OFF.
- Disconnect: HVAC Module C294a.
- Measure the resistance between SJB C2280b-29, circuit 1397 (GY/RD), harness side and ground.




- Is the resistance greater than 10,000 ohms?

Yes
GO to G12.

No
REPAIR circuit 1397 (GY/RD) for a short to ground. TEST the system for normal operation.

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G4 CHECK THE AIR CONDITIONING COMPRESSOR CYCLING SWITCH (ACCS) PCM PID WITH THE A/C OFF


- With the engine running, select the OFF position on the HVAC module.
- Enter the following diagnostic mode on the scan tool: ACCS PCM PID.
- Does the ACCS PCM PID read OFF?

Yes
GO to G5.

No
GO to G13.

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G5 CHECK THE AIR CONDITIONING CLUTCH (WAC/ACCR) PID WITH THE A/C OFF


- Enter the following diagnostic mode on the scan tool: WAC/ACCR PCM PID.
- With the engine running, select PANEL mode on the HVAC module and make sure the A/C button is OFF.
- Does the WAC/ACCR PCM PID read OFF?

Yes
GO to G6.

No
GO to G13.

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G6 CHECK THE A/C CLUTCH RELAY


- Ignition OFF.
- Disconnect: A/C Clutch Relay.
- Ignition ON.
- With the engine running, observe the A/C clutch operation.
- Does the A/C clutch engage?

Yes
GO to G7.

No
CARRY OUT the A/C clutch relay component test.
If the relay tests OK, GO to G8.

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G7 CHECK CIRCUIT 883 (PK/LB) FOR A SHORT TO VOLTAGE


- Ignition OFF.
- Disconnect: A/C Compressor Clutch Field Coil C100.
- Ignition ON.
- Measure the voltage between A/C compressor clutch field coil C100-1, circuit 883 (PK/LB), harness side and ground.




- Is any voltage present?

Yes
REPAIR circuit 883 (PK/LB) 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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G8 CHECK CIRCUIT 420 (DB/YE) FOR VOLTAGE


- Ignition OFF.
- Disconnect: PCM C175b.
- Disconnect: A/C Cycling Switch C130.
- Ignition ON.
- Measure the voltage between PCM C175b-15, circuit 420 (DB/YE), harness side and ground.




- Is any voltage present?

Yes
For 4.0L, REPAIR circuit 420 (DB/YE)/198 (DG/OG) for a short to voltage. TEST the system for normal operation.

For 4.6L and 5.4L, GO to G10.

No
GO to G9.

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G9 CHECK THE A/C CYCLING SWITCH


- Ignition OFF.
- Remove the A/C cycling switch from the vehicle.
- Measure the resistance between the A/C cycling switch pins.
- Is the resistance greater than 10,000 ohms?

Yes
GO to G13.

No
INSTALL a new A/C cycling switch. TEST the system for normal operation.

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G10 CHECK FOR A SHORT TO VOLTAGE


- Ignition OFF.
- Disconnect: Dual-Function Pressure Switch C1078.
- Ignition ON.
- Measure the voltage between PCM C175b-15, circuit 420 (DB/YE), harness side and ground.




- Is any voltage present?

Yes
REPAIR circuit 420 (DB/YE) for a short to voltage. TEST the system for normal operation.

No
REPAIR circuit 198 (DG/OG) for a short to voltage. TEST the system for normal operation.

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G11 CHECK THE SJB MODULE CONNECTION


- Clear the DTCs.
- Disconnect all the SJB connectors.
- Check for:
- corrosion.
- pushed-out pins.
- incorrectly seated connector.
- Connect and correctly seat all the SJB connectors.
- Operate the system.
- Does the concern return?

Yes
INSTALL a new SJB. 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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G12 CHECK THE MODULE CONNECTION


- Carry out the HVAC Module Cold Boot Process. HVAC Module Cold Boot Process
- Operate the system.
- Does the concern return?

Yes
INSTALL a new HVAC module. 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. TEST the system for normal operation.

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G13 CHECK THE PCM MODULE CONNECTION


- Clear the DTCs.
- Disconnect all the PCM connectors.
- Check for:
- corrosion.
- pushed-out pins.
- incorrectly seated connector.
- Connect and correctly seat all 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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