Pinpoint Test M: The Air Conditioning (A/C) Is Always On - A/C Compressor Does Not Cycle
Climate Control System
Pinpoint Test M: 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 Electrical Diagrams.
Refer to Wiring Diagram Set 55, Automatic Climate Control System for schematic and connector information Electrical Diagrams.
Normal Operation
When the A/C is requested, the Front Controls Interface Module (FCIM) sends the button press message over the Infotainment Controller Area Network (I-CAN) to the Instrument Panel Cluster (IPC) module. The IPC (Instrument Panel Cluster) module then sends the button press message to Body Control Module (BCM) over the High Speed Controller Area Network (HS-CAN). The BCM (Body Control Module) then sends the button press message to the HVAC module over the Medium Speed Controller Area Network (MS-CAN). Lastly the HVAC module sends an A/C request message through the MS-CAN (Medium Speed Controller Area Network) to the BCM (Body Control Module) and the BCM (Body Control Module) sends the A/C request through the HS-CAN (High Speed Controller Area Network) 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 compressor clutch field coil from the relay. Ground is supplied for the A/C compressor clutch field coil.
The evaporator discharge air temperature sensor is used for A/C compressor cycling. An accurate evaporator temperature is critical for compressor engagement. The PCM uses the temperature measurement to turn the A/C compressor off before the evaporator temperatures are cold enough to freeze the condensation on the evaporator core.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- PCM
- Evaporator discharge air temperature sensor
- A/C clutch relay
- A/C compressor clutch air gap
PINPOINT TEST M : THE AIR CONDITIONING (A/C) IS ALWAYS ON - A/C COMPRESSOR DOES NOT CYCLE
M1 CHECK THE A/C EVAPORATOR TEMPERATURE (EVAP_TEMP) HVAC PID
- Ignition ON.
- Allow the vehicle exterior and interior to stabilize to the ambient temperature.
- Enter the following diagnostic mode on the scan tool: HVAC DataLogger.
- Monitor the EVAP_TEMP HVAC PID
Does the EVAP_TEMP HVAC PID read similar to the ambient temperature?
Yes
GO to M2.
No
INSTALL a new evaporator discharge air temperature sensor. TEST the system for normal operation.
M2 CHECK THE AIR CONDITIONING COMPRESSOR COMMANDED STATE (ACC_CMD) PCM PID WITH THE A/C OFF
- Start the engine.
- Enter the following diagnostic mode on the scan tool: PCM DataLogger.
- Monitor the ACC_CMD PCM PID
- Select PANEL press the A/C button (indicator off) on the HVAC controls.
Does the ACC_CMD PCM PID read OFF?
Yes
GO to M3.
No
GO to M6.
M3 CHECK THE A/C COMPRESSOR CLUTCH ENGAGEMENT WITH RELAY DISCONNECTED
- Ignition OFF.
- Disconnect: A/C Clutch Relay.
- Start the engine.
- With the engine running, observe the A/C compressor clutch.
Is the compressor clutch disengaged?
Yes
GO to M4.
No
GO to M6.
M4 CHECK THE A/C CLUTCH RELAY
- Select PANEL and press the A/C button (indicator off) on the HVAC controls.
- With the engine running, connect a 12-volt test light between A/C clutch relay socket, circuit CBB70 (YE/BU) and A/C clutch relay socket, circuit CH302 (WH/BN).
Does the test light illuminate?
Yes
GO to M5.
No
INSTALL a new A/C clutch relay. TEST the system for normal operation.
M5 CHECK THE A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: PCM C175B (for 3.5L/3.7L engine) or C1381B (for 2.0L engine).
- For the 3.5L or 3.7L engine, measure the resistance between ground and PCM C175B-12, circuit CH302 (WH/BN), harness side.
- For the 2.0L engine, measure the resistance between ground and PCM C1381B-10, circuit CH302 (WH/BN), harness side.
Is the resistance greater than 10,000 ohms?
Yes
INSTALL a new A/C compressor.
No
REPAIR circuit CH302 (WH/BN) for a short to ground. TEST the system for normal operation.
M6 CHECK THE PCM CONNECTION
- Disconnect all the PCM connectors.
- Inspect the PCM component and harness side connectors for:
- corrosion
- damaged pins
- pushed-out terminals
- Connect and correctly seat all the PCM connectors.
- Clear the DTCs.
- Enter the following diagnostic mode on the scan tool: Self-Test- PCM.
- 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.