Inspection Procedure 23: A/C Switch System <Automatic A/C>


OPERATION

  • Battery voltage is applied from AC/S terminal on the engine-ECU connector through the dual pressure switch to the A/C-ECU connector.

FUNCTION

  • The A/C switch ON signal is sent from the A/C-ECU to the engine-ECU. The engine-ECU uses this signal to control the A/C compressor relay.

PROBABLE CAUSES

  • Failed dual pressure switch
  • Failed A/C-ECU
  • Open/short circuit or harness damage in A/C switch circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III data list

  • Data list reference table (Refer to ).

    1. Item 25: A/C switch

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).
Go to Step 2.

STEP 2. Perform voltage measurement at dual pressure switch

  • Disconnect connector, and measure at the harness side.
  • Ignition switch: ON
  • Voltage between terminal AC/S line and earth.
OK: System voltage

Q. Is the check result normal?
Go to Step 4.
Go to Step 3.

STEP 3. Check of open circuit, and short to earth in AC/S line between heater control unit connector and engine-ECU connector.

Q. Is the check result normal?
Replace the engine-ECU.
Repair the connector(s) or wiring harness.

STEP 4. Check the dual pressure switch.

  • Check the dual pressure switch (Refer to GROUP 55A - On-vehicle Service - Dual Pressure Switch Check).

Q. Is the check result normal?
Go to Step 5.
Replace the dual pressure switch.

STEP 5. Check of open circuit, short circuit, and damage in A/C line between dual pressure switch connector and A/C-ECU.

Q. Is the check result normal?
Go to Step 6.
Repair the connector(s) or wiring harness.

STEP 6. Check of damage in AC/S line between dual pressure switch and engine-ECU connector.

Q. Is the check result normal?
Go to Step 7.
Repair the connector(s) or wiring harness.

STEP 7. Perform voltage measurement at A/C-ECU connector.

  • Check the voltage at the A/C-ECU (Refer to GROUP 55B -Troubleshooting - Check at A/C-ECU Terminals).

Q. Is the check result normal?
Go to Step 8.
Replace the A/C-ECU.

STEP 8. M.U.T.-III data list

  • Data list reference table (Refer to ).

    1. Item 25: A/C switch

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 engine-ECU.