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, when the A/C is requested, an A/C request message is sent from the HVAC module over the Medium Speed Controller Area Network (MS-CAN) 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.
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 clutch from the relay. Ground is supplied for the A/C clutch.
The evaporator temperature sensor is used for A/C compressor cycling. An accurate evaporator temperature is critical for compressor engagement. The temperature measurement is used by the PCM 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 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 first.
M1 CHECK THE A/C EVAPORATOR TEMPERATURE (EVAP_TEMP) HVAC PID
- Ignition ON.
- Allow the vehicle exterior and interior to stabilize to the outside ambient temperature.
- 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 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: 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 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 the voltage greater than 10 volts?
Yes
CARRY OUT the A/C clutch relay component test. for component testing. If the relay tests OK, 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 any voltage present?
Yes
REPAIR circuit CH401 (VT/WH) for a short to voltage. TEST the system for normal operation.
No
GO to M5.
M5 CHECK THE A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: PCM C175B (Gasoline).
- Disconnect: PCM C1232B (Diesel).
- For gasoline engines
Measure the resistance between ground and PCM C175B-12, circuit CH302 (WH/BN), harness side.
- For diesel engines
Measure the resistance between ground and PCM C1232B-2, circuit CH302 (WH/BN), harness side.
Is the resistance greater than 10,000 ohms?
Yes
GO to M6.
No
REPAIR circuit CH302 (WH/BN) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
M6 CHECK THE PCM CONNECTION
- Disconnect all the PCM connectors.
- Inspect the HVAC 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.