Inspection Procedure 21: A/C Compressor Relay System


OPERATION



  • Battery voltage is applied to the A/C compressor relay connector terminal.
  • Engine-ECU connector terminal AC/R applies current to the A/C compressor relay coil by turning ON the power transistor in the unit in order to turn the relay ON.
  • When the A/C compressor relay turns ON, battery voltage is supplied by the A/C compressor relay connector terminal to the A/C compressor connector terminal.

FUNCTION



  • When the A/C switch ON signal is input into the engine-ECU, the engine-ECU turns ON the A/C compressor relay. This causes battery voltage to be supplied to the A/C compressor assembly and the A/C compressor clutch actuates.

PROBABLE CAUSES



  • Failed A/C compressor relay
  • Failed A/C compressor assembly
  • Open/short circuit or harness damage in A/C compressor relay circuit, or loose connector contact.
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check A/C compressor relay itself.

  • A/C compressor relay connector check.
  • Check A/C compressor relay itself (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.

  • Disconnect relay, and measure at 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.

    Check and repair harness between battery and A/C compressor relay connector terminals.

    • Check power supply line for open/short circuit.

STEP 3. 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 4.
Repair the damaged harness wire.

STEP 4. Perform voltage measurement at engine-ECU connector.

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

Q. Is the check result normal?
Go to Step 5.

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

    • Check signal line for open/short circuit.

STEP 5. Check harness between A/C compressor relay connector terminal and engine-ECU connector terminal AC/R.

  • Check signal line for damage.

Q. Is the check result normal?
Go to Step 6.
Repair the damaged harness wire.

STEP 6. Check harness between A/C compressor relay connector terminal and A/C compressor assembly connector terminal.

  • Check power supply line for open/short circuit and damage.

Q. Is the check result normal?
Go to Step 7.
Repair or replace the connector, or repair the damaged harness wire.

STEP 7. Check A/C compressor clutch operating conditions.

  • Disconnect engine-ECU connector, and short-circuit terminal AC/R to the body earth.
OK: A/C compressor clutch operates.

Q. Is the check result normal?
Replace the engine-ECU.
Replace the A/C compressor assembly.