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Air Conditioning Compressor Malfunction

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    • Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

A/C Compressor Clutch Relay Coil Ignition

P0645, P0646

P0645, P0647

--

--

A/C Compressor Clutch Relay Switch B+

1

1

--

--

A/C Compressor Clutch Relay Coil Control

P0645, P0646

P0645, P0647

P0645, P0647

3

A/C Compressor Control

1

1

2

-

A/C Compressor Ground

1

1

--

--

1. A/C Compressor Inoperative

2. A/C Compressor Always ON

3. A/C Compressor Malfunction

Circuit/System Description

When the A/C switch is pressed, the HVAC control module sends an A/C request message to the engine control module (ECM) via CAN-Bus. Therefore the ECM grounds the A/C compressor clutch relay control circuit, which will switch the A/C compressor clutch relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch. The A/C compressor clutch will be activated.

Diagnostic Aids

The following conditions must be met in order for the ECM to turn on the A/C compressor clutch:

    • Battery voltage is between 9-18 V.
    • Engine coolant temperature is less than 124°C (255°F).
    • Engine speed is greater than 600 RPM.
    • Engine speed is less than 5 500 RPM.
    • A/C high side pressure is between 269-2 929 kPa (39-425 PSI).
    • Throttle position is less than 100%.
    • Evaporator temperature is greater than 3°C (38°F).
    • ECM does not detect immoderate torque load.
    • ECM does not detect insufficient idle quality.
    • The ambient temperature is above 1°C (34°F).

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

Note: Before executing Circuit/System Testing, all conditions shown in Diagnostic Aids must be met.

  1. Ignition ON, activate and deactivate the A/C switch. Verify the scan tool A/C Switch parameter changes between Active and Inactive.
    2. ⇒If not the specified value, replace the A26 HVAC Control.
  2. Activate and deactivate the A/C switch. Verify the engine control module (ECM) scan tool A/C Request Signal parameter changes between Active and Inactive.
    3. ⇒If not the specified value, replace the K33 HVAC Control Module.
  3. Ignition OFF, remove the KR29 A/C Compressor Clutch Relay.
  4. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
    5. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
    6. ⇒If the test lamp illuminates, test the control circuit for a short to voltage.
  6. Ignition OFF, disconnect the harness connector at the Q2 A/C Compressor Clutch.
  7. Test for less than 5 Ω between the Q2 A/C Compressor Clutch ground circuit terminal A and ground.
    8. ⇒If greater than the specified value, test the ground circuit for an open/high resistance.
  8. Connect the harness connector at the Q2 A/C Compressor Clutch.
  9. Ignition ON, connect a 10 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the Q2 A/C Compressor Clutch is activated.
    10. ⇒If the Q2 A/C Compressor Clutch does not activate, test the control circuit for an open/high resistance. If the circuit test normal, replace the Q2 A/C Compressor Clutch.
  10. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
  11. Command the engine control module (ECM) A/C Relay output function ON and OFF with the scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    12. ⇒If the test lamp always illuminates or always does not illuminate, replace the K20 Engine Control Module.
  12. If all circuits test normal, replace the KR29 A/C Compressor Clutch Relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Air Conditioning Compressor Replacement : LNP → LUJ → LXT, L2W → LDE, LFH, LLU, LXV, and 2H0 → LLW
    •  Heater and Air Conditioning Control Replacement
    • Control Module References for HVAC control module or engine control module replacement, setup, and programming.
   


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