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

Climate Control System

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

Normal Operation

Under normal operation, voltage is provided to the function selector switch. When A/C is requested, voltage is sent from the function selector switch to the A/C cycling switch. Voltage is sent from the A/C cycling switch through the A/C high pressure switch to the PCM.

Voltage is provided to the A/C clutch relay coil and switch contacts. 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 clutch from the relay. Ground is supplied for the A/C clutch.

This pinpoint test is intended to diagnose the following:

- Wiring, terminals or connectors

- PCM

- Function selector switch

- A/C clutch relay

- A/C compressor 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.

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.

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.

F3 CHECK THE A/C HIGH PRESSURE SWITCH TO A/C CYCLING SWITCH CIRCUIT FOR A SHORT TO VOLTAGE

- Ignition OFF.

- Disconnect: A/C High Pressure Switch C1078.

- Ignition ON.

- 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.

F4 CHECK THE A/C HIGH PRESSURE SWITCH TO PCM CIRCUIT FOR A SHORT TO VOLTAGE

- Ignition OFF.

- Disconnect:For 4.6L and 5.4L engines, PCM C175B.

- Disconnect:For 6.8L engines, PCM C1551E.

- Ignition ON.

- 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.

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.

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 A/C compressor clutch field coil C100-1, circuit CH401 (VT/WH), 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.

F7 CHECK THE A/C COMPRESSOR CLUTCH FIELD COIL VOLTAGE CIRCUIT FOR A SHORT TO VOLTAGE

- Ignition OFF.

- Disconnect: A/C Clutch Relay.

- Ignition ON.

- Measure the voltage between ground and A/C compressor clutch field coil C100-1, circuit CH401 (VT/WH), harness side.





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.

F8 CHECK THE PCM CONNECTION

- Disconnect all the PCM connectors.

- Inspect the HVAC module connectors for:
- corrosion.
- pushed-out terminals.
- damaged terminals.


- Connect and correctly seat all the PCM connectors.

- Clear the DTCs.

- Operate the system and verify the concern is still present.

Is the concern still present?

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.