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
Normal Operation
Under normal operation, for vehicles equipped with navigation, when the 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 Instrument Cluster (IC), then from the IC (Instrument Cluster) through the High Speed Controller Area Network (HS-CAN) bus to the PCM. When MAX A/C is selected on the touch screen, the Audio Control Module (ACM) 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, the HVAC module sends an A/C request message 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.
Voltage is provided to the A/C clutch relay switch. When the PCM energizes the relay, voltage is supplied to the A/C clutch from the relay. Ground is supplied for the A/C clutch.
The evaporator discharge air temperature sensor is used for A/C compressor cycling. An accurate evaporator discharge air temperature is critical for compressor engagement. The temperature measurement is used by the PCM to turn off the A/C compressor when the evaporator temperatures are cold enough to freeze the condensation.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- PCM
- A/C evaporator discharge temperature sensor
- A/C control relay
- A/C clutch air gap
PINPOINT TEST M : THE AIR CONDITIONING (A/C) IS ALWAYS ON - A/C COMPRESSOR DOES NOT CYCLE
NOTE: Before carrying out the following test, diagnose any HVAC, PCM or IC (Instrument Cluster) DTCs.
M1 CHECK THE A/C EVAPORATOR TEMPERATURE (EVAP_TEMP) HVAC PID
- Ignition ON.
- 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.
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 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 M5.
No
GO to M3.
M3 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.
- With the engine running, measure the voltage between A/C compressor clutch field coil C100-1, circuit CH401 (VT/WH), harness side and ground.
Is the voltage greater than 10 volts?
Yes
GO to M4.
No
ADJUST the A/C compressor clutch gap. REFER to Air Conditioning (A/C) Clutch Air Gap Adjustment . TEST the system for normal operation.
M4 CHECK THE A/C COMPRESSOR CLUTCH FIELD COIL VOLTAGE CIRCUIT 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 CH401 (VT/WH), harness side and ground.
Is the voltage greater than 10 volts?
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. TEST the system for normal operation.
M5 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.