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 55, Automatic Climate Control System for schematic and connector information. Diagrams By Number
Normal Operation
Under normal operation, when A/C is requested, a message is sent over the bus from the electronic automatic temperature control (EATC) module, through the instrument cluster, to the powertrain control module (PCM). The PCM receives input from the A/C cycling switch through circuit 883 (PK/LB). Voltage is provided to the A/C cycling switch through circuit 1040 (RD/BK)/348 (VT).
The PCM provides a ground for the A/C clutch relay coil through circuit 73 (OG/LB). The A/C clutch relay coil receives voltage through circuit 391 (RD/YE). Voltage for the A/C clutch relay switch is provided through circuit 1810 (LG/OG). When the relay is activated, voltage is supplied to the A/C clutch solenoid through circuit 321 (GY/WH). Ground is supplied for the A/C clutch through circuit 57 (BK).
The A/C cycling switch is used for A/C compressor cycling. The switch is used by the PCM to turn off the A/C compressor before the line pressures are low enough to drop the evaporator temperature excessively low and freeze the condensation.
When an A/C request is received by the PCM, the A/C compressor clutch will only be engaged through the A/C clutch relay if all of the following conditions are met:
- The PCM does not detect excessively high or low refrigerant pressure from the A/C pressure transducer.
- The PCM does not detect excessively low refrigerant pressure from the A/C cycling switch.
- The PCM does not detect excessively high engine coolant temperature.
- The PCM does not detect an ambient air temperature too low.
- The PCM has not detected a wide open throttle (WOT) condition.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- PCM
- A/C clutch relay
- HVAC module
- A/C cycling switch
- A/C clutch air gap
PINPOINT TEST P: THE AIR CONDITIONING (A/C) IS ALWAYS ON - A/C COMPRESSOR DOES NOT CYCLE
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P1 CHECK THE AIR CONDITIONING COMPRESSOR CYCLING SWITCH (ACCS) PCM PID WITH THE A/C OFF
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: ACCS PCM PID.
- Press the OFF manual override button on the EATC module.
- Does the ACCS PCM PID read OFF?
Yes
GO to P4.
No
GO to P2.
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P2 CHECK THE A/C CYCLING SWITCH
- Ignition OFF.
- Disconnect: A/C Cycling Switch C1081.
- Start the engine.
- Enter the following diagnostic mode on the scan tool: ACCS PCM PID.
- Press the OFF manual override button on the EATC module.
- Does the ACCS PCM PID read OFF?
Yes
INSTALL a new A/C cycling switch. TEST the system for normal operation.
No
GO to P3.
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P3 CHECK CIRCUIT 883 (PK/LB) FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: A/C Cycling Switch C1081.
- Measure the voltage between A/C cycling switch C1081-1, 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
GO to P6.
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P4 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 A/C compressor clutch field coil C100-1, circuit 321 (GY/WH), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to P5.
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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P5 CHECK CIRCUIT 321 (GY/WH) FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: A/C Clutch Relay.
- Ignition ON.
- Measure the voltage between A/C compressor clutch field coil C100-1, circuit 321 (GY/WH), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
REPAIR circuit 321 (GY/WH) for a short to voltage. TEST the system for normal operation.
No
INSTALL a new A/C clutch relay. CHECK the A/C clutch diode. TEST the system for normal operation. INSTALL a new diode if necessary.
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P6 CHECK THE PCM CONNECTION
- Disconnect all the PCM connectors.
- Inspect the 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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