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




Climate Control System


Pinpoint Tests


Pinpoint Test F: 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 23 for schematic and connector information. Diagrams By Number

Refer to Wiring Diagram Set 24 for schematic and connector information. Diagrams By Number

Refer to Wiring Diagram Set 25 for schematic and connector information. Diagrams By Number

Refer to Wiring Diagram Set 26 for schematic and connector information. Diagrams By Number

Normal Operation

Under normal operation, voltage is provided to the function selector switch through circuit CBP37 (WH). When A/C is requested, voltage is sent from the function selector switch to the A/C cycling switch through circuit CH434 (GY/YE). Voltage is sent from the A/C cycling switch to the dual-function pressure switch (diesel engine) or the A/C high pressure switch (gasoline engine) through circuit CH423 (YE). Voltage is sent from the dual-function pressure switch (diesel engine) or the A/C high pressure switch (gasoline engine) to the PCM through circuit CH419 (BU).

The PCM provides a ground for the A/C clutch relay coil through circuit CH302 (WH/BN). The A/C clutch relay coil receives ignition voltage through circuit CBB77 (WH). Battery voltage for the A/C clutch relay switch is provided through circuit SBB29 (GY/RD). When the relay is energized, voltage is supplied to the A/C clutch field coil through circuit (gasoline engine) CH401 (WH/VT) or (diesel engine) CH401 (WH/VT)/321 (GY/WH). Ground is supplied for the A/C clutch through circuit (gasoline engine) GD123 (BK/GY) or (diesel engine) 57 (BK).

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



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

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

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F1 CHECK THE AIR CONDITIONING COMPRESSOR COMMANDED STATE (ACC_CMD) PCM PID WITH THE A/C ON


- Ignition ON.
- Place the function selector switch to the OFF position.
- Enter the following diagnostic mode on the scan tool: ACC_CMD PCM PID.
- Does the ACC_CMD PCM PID read YES?

Yes
GO to F8.

No
GO to F2.

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F2 CHECK THE AIR CONDITIONING REQUEST SIGNAL (AC_REQ) PCM PID WITH THE A/C OFF


- Enter the following diagnostic mode on the scan tool: AC_REQ PCM PID.
- Place the function selector switch to the OFF position.
- Does the AC_REQ PCM PID read YES?

Yes
GO to F3.

No
GO to F5.

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F3 CHECK CIRCUIT CH423 (YE) FOR VOLTAGE


- Ignition OFF.
- Disconnect: For diesel engines, Dual Function Pressure Switch C1062.
- Disconnect: For gasoline engines, A/C High Pressure Switch C1078.
- Ignition ON.

For diesel engines




- For diesel engines: Measure the voltage between dual function pressure switch C1062-1, circuit CH423 (YE) and ground.

For gasoline engines




- For gasoline engines: Measure the voltage between A/C high pressure switch C1078-3, circuit CH423 (YE) and ground.
- Is any voltage present?

Yes
REPAIR circuit CH423 (YE) for a short to voltage. TEST the system for normal operation.

No
GO to F4.

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F4 CHECK CIRCUIT CH419 (BU) OR CH421 (GY) FOR A SHORT TO VOLTAGE


- Ignition OFF.
- Disconnect: For diesel engines, PCM C1381b.
- Disconnect: For 4.6L & 5.4L gasoline engines, PCM C175b.
- Disconnect: For 6.8L gasoline engines, PCM C1551e.
- Ignition ON.

For diesel engines




- For diesel engines: Measure the voltage between dual function pressure switch C1062-4, circuit CH419 (BU) and ground.

For gasoline engines




- For gasoline engines: Measure the voltage between dual function pressure switch C1078-1, circuit CH421 (GY) and ground.
- Is any voltage present?

Yes
REPAIR circuit CH419 (BU) or CH421 (GY) for a short to voltage. TEST the system for normal operation.

No
GO to F8.

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F5 CHECK THE A/C CYCLING SWITCH


- Ignition OFF.
- Disconnect: A/C Cycling Switch C130.
- Remove the A/C cycling switch from the vehicle.
- Measure the resistance between the A/C cycling switch terminals.




- Is the resistance greater than 10,000 ohms?

Yes
GO to F6.

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

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F6 CHECK FOR VOLTAGE TO THE A/C COMPRESSOR CLUTCH FIELD COIL


- Ignition OFF.
- Disconnect: A/C Compressor Clutch Field Coil C100.
- Ignition ON.
- Measure the voltage between ground and:
- For diesel engines, A/C compressor clutch field coil C100-1, circuit CH321 (GY/WH), harness side.
- For gasoline engines, A/C compressor clutch field coil C100-1, circuit CH401 (WH/VT), harness side.




- Is any voltage present?

Yes
GO to F7.

No
ADJUST the A/C compressor clutch air gap. REFER to Air Conditioning (A/C) Clutch Air Gap Adjustment Adjustments. TEST the system for normal operation.

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F7 CHECK CIRCUIT CH401 (WH/VT) FOR A SHORT TO VOLTAGE


- Ignition OFF.
- Disconnect: A/C Control Relay.
- Ignition ON.
- Measure the voltage between ground and:
- For diesel engines, A/C compressor clutch field coil C100-1, circuit CH321 (GY/WH), harness side.
- For gasoline engines, A/C compressor clutch field coil C100-1, circuit CH401 (WH/VT), harness side.




- Is any voltage present?

Yes
REPAIR circuit CH401 (WH/VT) or CH321 (GY/WH) for a short to voltage. TEST the system for normal operation.

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

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F8 CHECK THE PCM 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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