Pinpoint Test J: The Air Conditioning (A/C) is Always On
Climate Control System
Pinpoint Test J: The Air Conditioning (A/C) is Always On
Refer to Wiring Diagram Set 55 (Fusion/Milan/MKZ, Fusion Hybrid, Milan Hybrid, MKZ Hybrid), Automatic Climate Control System for schematic and connector information. Diagrams By Number
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 bus to the Instrument Cluster (IC), then from the IC through the High Speed Controller Area Network (HS-CAN) bus to the PCM.
For vehicles equipped with navigation, when MAX A/C is selected on the touch screen, the Audio Control Module (ACM) sends a message over the MS-CAN 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 bus to the IC, then from the IC through the HS-CAN 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 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 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
- FCIM
- ACM
- Electric A/C compressor
- A/C evaporator discharge temperature sensor
- A/C pressure transducer
PINPOINT TEST J: THE AIR CONDITIONING (A/C) IS ALWAYS ON
NOTE: Diagnose any PCM, HVAC module or ACCM DTCs before carrying out the following pinpoint test.
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J1 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
For vehicles not equipped with navigation, GO to J2.
For vehicles equipped with navigation, GO to J3.
No
INSTALL a new A/C evaporator discharge temperature sensor. TEST the system for normal operation.
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J2 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 J4.
No
INSTALL a new HVAC module. TEST the system for normal operation.
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J3 CHECK THE (A/C) SWITCH (CC_SW_AC) FCIM PID WITH THE A/C OFF
NOTE: Before carrying out this test step, be sure all other FCIM button functions are functioning correctly. If all other buttons operate correctly, continue with this test step. If multiple buttons are incorrectly functioning and DTC U0256:00 is not present, install a new FCIM. Test the system for normal operation. If DTC U0256:00 is present, diagnose the DTC first.
- Start the engine.
- Enter the following diagnostic mode on the scan tool: CC_SW_AC FCIM PID.
- Select PANEL and make sure the A/C indicator is OFF.
- Does the CC_SW_AC FCIM PID read Inactive?
Yes
GO to J4.
No
INSTALL a new FCIM. REFER to Information and Entertainment Systems Service and Repair. TEST the system for normal operation.
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J4 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. REFER to Climate Control Service and Repair. TEST the system for normal operation.
No
INSTALL a new PCM. TEST the system for normal operation.
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