Pinpoint Test P: The Air Conditioning (A/C) is Always On

Climate Control System

Pinpoint Test P: The Air Conditioning (A/C) is Always On

Refer to Wiring Diagram Set 55, Automatic Climate Control System for schematic and connector information Electrical Diagrams.

When A/C is requested, a message is sent from the HVAC module over the MS-CAN (Medium Speed Controller Area Network) bus to the IC (Instrument Cluster), then from the IC (Instrument Cluster) through the HS-CAN (High Speed Controller Area Network) bus to the PCM.

When an A/C request is received from the HVAC module, an A/C demand message is sent from the PCM over the HS-CAN (High Speed Controller Area Network) bus to the Air Conditioning Compressor Module (ACCM) 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 high engine coolant temperature.

- The PCM does not detect an ambient air temperature below -1°C (30°F).

- The PCM has not detected a Wide Open Throttle (WOT) condition.

- The HVAC module does not detect an evaporator discharge air temperature below 2°C (36°F).

When the ACCM (Air Conditioning Compressor Module) receives the A/C demand message, it will engage. Instead of cycling ON and OFF like a traditional A/C compressor, the PCM monitors the evaporator discharge temperature from the HVAC module to raise or lower the electric A/C compressor speed as required.

This pinpoint test is intended to diagnose the following:

- HVAC module

- Electric A/C compressor

- A/C evaporator discharge temperature sensor

- A/C pressure transducer

PINPOINT TEST P : THE AIR CONDITIONING (A/C) IS ALWAYS ON

NOTE: Diagnose any PCM, HVAC module or ACCM (Air Conditioning Compressor Module) DTCs before carrying out the following pinpoint test.

P1 CHECK THE A/C EVAPORATOR TEMPERATURE (EVAP_TEMP) HVAC PID

- Allow the vehicle exterior and interior to stabilize to an ambient temperature.

- Ignition ON.

- Enter the following diagnostic mode on the scan tool: EVAP_TEMP HVAC PID.

Does the EVAP_TEMP HVAC PID read similar to the ambient temperature?

Yes
GO to P2.

No
INSTALL a new A/C evaporator discharge temperature sensor. TEST the system for normal operation.

P2 CHECK THE (A/C) SWITCH (CC_SW_AC) HVAC PID WITH THE A/C OFF

- Start the engine.

- Enter the following diagnostic mode on the scan tool: CC_SW_AC HVAC PID.

- Select PANEL and make sure the A/C indicator is OFF.

Does the CC_SW_AC HVAC PID read Inactive?

Yes
GO to P3.

No
INSTALL a new HVAC module. TEST the system for normal operation.

P3 CHECK THE AIR CONDITIONING COMPRESSOR COMMANDED STATE (ACC_CMD) PCM PID WITH THE A/C OFF

- Enter the following diagnostic mode on the scan tool: ACC_CMD PCM PID.

- Select PANEL and make sure the A/C indicator is OFF.

Does the ACC_CMD PCM PID read OFF?

Yes
INSTALL a new electric A/C compressor. TEST the system for normal operation.

No
INSTALL a new PCM. TEST the system for normal operation.