Pinpoint Test P: The Air Conditioning (A/C) is Always On - A/C Compressor Does Not Cycle
Climate Control System
Pinpoint Test P: The Air Conditioning (A/C) is Always On - A/C Compressor Does Not Cycle
Normal Operation
For vehicles equipped with navigation, when A/C button is pressed, a message is sent from the Front Controls Interface Module (FCIM) over the Medium Speed Controller Area Network (MS-CAN) bus to the HVAC module. The HVAC module then sends an A/C request message over the MS-CAN (Medium Speed Controller Area Network) bus to the Body Control Module (BCM), then from the BCM (Body Control Module) through the High Speed Controller Area Network (HS-CAN) bus to the PCM. When MAX A/C is selected on the touch screen, the Front Display Interface Module (FDIM) sends a message over the MS-CAN (Medium Speed Controller Area Network) bus to the HVAC module that MAX A/C has been selected.
For vehicles not equipped with navigation, 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 BCM (Body Control Module), then from the BCM (Body Control Module) through the HS-CAN (High Speed Controller Area Network) bus to the PCM.
Voltage is provided to the A/C clutch relay coil from Battery Junction Box (BJB) fuse 77 (10A) and switch contacts from Battery Junction Box (BJB) fuse 30 (10A). 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 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 temperature sensor
- A/C clutch relay
- A/C compressor clutch air gap
PINPOINT TEST P : THE AIR CONDITIONING (A/C) IS ALWAYS ON - A/C COMPRESSOR DOES NOT CYCLE
NOTE:
Before carrying out the following test, diagnose any HVAC or PCM or DTCs.
P1 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 P2.
No
INSTALL a new heater core and evaporator core housing. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
P2 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: 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 P3.
No
GO to P7.
P3 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 P4.
No
GO to P6.
P4 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 CBB77 (WH) and A/C clutch relay socket, circuit CH302 (WH/BN).
Does the test light illuminate?
Yes
GO to P5.
No
INSTALL a new A/C clutch relay. TEST the system for normal operation.
P5 CHECK THE A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: PCM C1381B (5.0L, 6.2L).
- Disconnect: PCM C175B (3.7L).
- Disconnect: PCM C1551B (3.5L).
- For 3.7L, 5.0L and 6.2L
Measure the resistance between ground and:
- For 3.7L, PCM C175B-12, circuit CH302 (WH/BN), harness side.
- For 5.0L and 6.2L, PCM C1381B-12, circuit CH302 (WH/BN), harness side.
- For 3.5L
For 3.5L, measure the resistance between ground and PCM C1551B-2, circuit CH302 (WH/BN), harness side.
Is the resistance greater than 10,000 ohms?
Yes
GO to P7.
No
REPAIR circuit CH302 (WH/BN) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
P6 CHECK FOR VOLTAGE TO THE A/C COMPRESSOR CLUTCH FIELD COIL
- Ignition OFF.
- Disconnect: A/C Compressor Clutch Field Coil C100.
- Ignition ON.
- Select the OFF position on the HVAC module.
- Measure the voltage between A/C compressor clutch field coil C100-1, 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
ADJUST the A/C compressor clutch gap. REFER to Air Conditioning (A/C) Clutch Air Gap Adjustment . TEST the system for normal operation.
P7 CHECK THE PCM CONNECTION
- Disconnect all the PCM connectors.
- Inspect the PCM connectors for:
- corrosion
- pushed-out terminals
- damaged 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.