Air Conditioning Compressor Malfunction (LLU)
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Air Conditioning Compressor Malfunction (LLU)
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Diagnostic Fault Information
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Circuit
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Short to Ground
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Open/High Resistance
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Short to Voltage
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Signal Performance
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A/C Compressor Clutch Relay Coil Ignition
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P0646
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P0645, P0646
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-
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-
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A/C Compressor Clutch Relay Switch B+
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1
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1
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-
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-
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A/C Compressor Clutch Relay Coil Control
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P0646
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P0645, P0646
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P0647
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3
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A/C Compressor Control
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1
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1
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2
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-
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A/C Compressor Ground
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1
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1
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-
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-
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1. A/C Compressor Inoperative
2. A/C Compressor Always ON
3. A/C Compressor Malfunction
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Circuit/System Description
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When the A/C switch is pressed, the HVAC control module sends an A/C request signal to the engine control module (ECM) via the CAN bus. The ECM therefore grounds the A/C compressor clutch relay control circuit, which activates the clutch relay. Battery voltage is supplied via the relay contacts to the A/C compressor clutch which is then activated.
The following conditions must be met in order for the ECM to turn on the A/C compressor clutch:
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Battery voltage is between 9-18 V.
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Engine coolant temperature is less than 124°C (255°F).
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Engine speed is greater than 600 rpm.
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Engine speed is less than 5 500 rpm.
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A/C high side pressure is between 269-2 929 kPa (39-425 PSI).
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Throttle position is less than 100%.
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Evaporator temperature is greater than 3°C (38°F).
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ECM does not detect immoderate torque load.
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ECM does not detect insufficient idle quality.
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The ambient temperature is above 1°C (34°F).
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Schematic Reference
HVAC Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Automatic HVAC Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information
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Note
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Before executing Circuit/System Testing, all conditions shown in Diagnostic Aids must be met.
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1.
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Ignition ON, activate and deactivate the A/C switch. Verify the scan tool A/C Switch parameter changes between Active and Inactive.
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2.
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If not the specified value, replace the A20 Radio/HVAC Controls.
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3.
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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.
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4.
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If not the specified value, replace the K33 HVAC Control Module.
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5.
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Ignition OFF, remove the KR29 A/C Compressor Clutch Relay.
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6.
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Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
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7.
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If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit test normal, replace the X50A Fuse Block - Underhood.
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8.
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Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
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9.
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If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit test normal, replace the X50A Fuse Block - Underhood.
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10.
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Ignition OFF, disconnect the harness connector at the Q2 A/C Compressor Clutch.
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11.
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Test for less than 5 Ω between the Q2 A/C Compressor Clutch ground circuit terminal A and ground.
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12.
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If greater than the specified range, test the ground circuit for an open/high resistance.
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13.
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Connect the harness connector at the Q2 A/C Compressor Clutch.
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14.
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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.
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15.
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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.
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16.
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Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
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17.
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Command the engine control module (ECM) A/C Compressor Clutch Relay output function ON and OFF with the scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
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18.
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If the test lamp always illuminates or always does not illuminate, replace the K20 Engine Control Module.
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19.
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If all circuits test normal, replace the KR29 A/C Compressor Clutch Relay.
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Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
