Inspection Procedure 18: A/C Compressor Relay System




OPERATION




FUNCTION




PROBABLE CAUSE




DIAGNOSIS PROCEDURE


STEP 1. Check A/C compressor relay.



  • A/C compressor relay connector check.
  • Check A/C compressor relay (Refer to GROUP 55 - On-vehicle Service - Relay Check ).

Q. Is the check result normal?

Go to Step 2.
Repair or replace the connector, or replace the A/C compressor relay.

STEP 2. Perform voltage measurement at A/C compressor relay connector.



  • Remove relay, and measure at the relay box side.
  • Voltage between terminal power supply lines and body earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 3.

    Repair or replace the connector, or check and repair harness between A/C compressor relay connector terminal and battery.

    • Check power supply line for open/short circuit.

STEP 3. Perform voltage measurement at engine-ECU connector.



  • Disconnect connector, and measure at the harness side.
  • Voltage between terminal AC/R and body earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 4.

    Repair or replace the connector, or check and repair harness between engine-ECU connector terminal AC/R and A/C compressor relay connector terminal.

    • Check earthing line for open/short circuit.

STEP 4. Perform voltage measurement at A/C compressor assembly connector.



  • Disconnect connector, and measure at the harness side.
  • Using a jumper wire, connect engine-ECU connector terminal AC/R and body earth.
  • Voltage between terminal output line and body earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 7.
Go to Step 5.

STEP 5. Check harness between A/C compressor relay connector terminal and A/C compressor assembly connector terminal.



  • Check output line for open/short circuit.

Q. Is the check result normal?

Go to Step 6.
Repair or replace the connector, or repair the damaged harness wire.

STEP 6. Check harness between A/C compressor relay connector terminal and engine-ECU connector terminal AC/R.



  • Check earthing line for damage.

Q. Is the check result normal?


    Repair or replace the connector, or check and repair harness between A/C compressor relay connector terminal and battery.

    • Check power supply line for damage.
Repair or replace the connector, or repair the damaged harness wire.

STEP 7. Check harness between battery and A/C compressor relay connector terminal.



  • Check power supply line for damage.

Q. Is the check result normal?

Go to Step 8.
Repair or replace the connector, or repair the damaged harness wire.

STEP 8. Check harness between A/C compressor relay connector terminal and A/C compressor assembly connector terminal.



  • Check output line for damage.

Q. Is the check result normal?

Go to Step 9.
Repair or replace the connector, or repair the damaged harness wire.

STEP 9. Perform voltage measurement at engine-ECU connector.



  • Disconnect engine-ECU harness, and connect special tool power plant ECU check harness (MB992291) to measure at connector for inspection.
  • Engine: Idle operation after warm-up

  • A/C set temperature:

    • Maximum Cool when temperature in cabin is 25°C or more
      Maximum Hot when temperature in cabin is 25°C or less
  • Voltage between terminal AC/R and body earth.
OK:
    1.0 V or less (when A/C is ON)
    System voltage (when A/C is OFF)

Q. Is the check result normal?

Go to Step 10.
Replace the engine-ECU.

STEP 10. M.U.T.-III actuator test.



  • Refer to Actuator Test Reference Table .

  1. Item 4: A/C compressor relay

Q. Is the check result normal?

Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Replace the A/C compressor relay.