Pinpoint Test N: The Air Conditioning (A/C) Is Always on - A/C Compressor Does Not Cycle
Climate Control System
Pinpoint Tests
Pinpoint Test N: 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 55, Automatic Climate Control System for schematic and connector information. Diagrams By Number
Normal Operation
Under normal operation, when A/C is requested in Electronic Automatic Temperature Control (EATC) or Dual Automatic Temperature Control (DATC) systems, a message is sent over the Medium Speed Controller Area Network (MS-CAN) bus to the Instrument Cluster (IC), then from the IC through the High Speed Controller Area Network (HS-CAN) bus to the PCM; or a voltage is sent to the IC through circuit CH434 (GY/YE), then a message is sent from the IC through the HS-CAN bus to the PCM Electronic Manual Temperature Control (EMTC) systems.
Ignition voltage for the A/C clutch relay switch is provided through circuit SBB25 (RD). When the PCM energizes the relay, ignition voltage is supplied to the A/C clutch through circuit CH401 (VT/WH). Ground is supplied for the A/C clutch through circuit GD121 (BK/YE).
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- PCM
- A/C evaporator discharge temperature sensor
- A/C pressure transducer
- A/C control relay
- A/C clutch air gap
PINPOINT TEST N: THE AIR CONDITIONING (A/C) IS ALWAYS ON - A/C COMPRESSOR DOES NOT CYCLE
NOTE: When disconnecting and reconnecting the pressure transducer electrical connector, make sure that the connector-locking device is in place and that the locking device and connector are correctly and fully seated.
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N1 CHECK THE A/C PRESSURE SENSOR (ACP_PRESS) PCM PID
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: ACP_PRESS PCM PID.
- With the R-134a Manifold Gauge Set connected, compare the pressure readings of the R-134a Manifold Gauge Set and the ACP_PRESS PCM PID.
- Are the pressure values of the R-134a Manifold Gauge Set and the ACP_PRESS PCM PID similar?
Yes
GO to N2.
No
INSTALL a new A/C pressure transducer. TEST the system for normal operation.
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N2 CHECK THE A/C EVAPORATOR TEMPERATURE (EVAP_TEMP) HVAC PID (3.5L ONLY) OR EVAPORATOR TEMPERATURE (A/CT) PCM PID
- Allow the vehicle exterior and interior to stabilize to an ambient temperature above 16°C (60°F).
- Enter the following diagnostic mode on the scan tool: EVAP_TEMP HVAC PID (3.5L only) or A/CT PCM PID.
- Does the EVAP_TEMP HVAC PID (3.5L ONLY) or A/CT PCM PID read similar to the ambient temperature?
Yes
GO to N3.
No
INSTALL a new A/C evaporator discharge temperature sensor. TEST the system for normal operation.
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N3 CHECK AIR CONDITIONING CLUTCH (WAC/ACCR) PCM PID WITH THE A/C OFF
- Enter the following diagnostic mode on the scan tool: WAC/ACCR PCM PID.
- Select the OFF position on the HVAC module.
- Does the WAC/ACCR PCM PID read ON?
Yes
GO to N6.
No
GO to N4.
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N4 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-B, circuit CH401 (VT/WH), harness side and ground.
- Is any voltage present?
Yes
GO to N5.
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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N5 CHECK CIRCUIT CH401 (VT/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-B, circuit CH401 (VT/WH), harness side and ground.
- 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. CHECK the A/C clutch diode. INSTALL a new diode if necessary. TEST the system for normal operation.
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N6 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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