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 Diagrams for schematic and connector information. Diagrams By Number
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.
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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 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.
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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.
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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 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.
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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.
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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.
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