Inspection Procedure 22: A/C Switch System <Manual A/C>


OPERATION

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

FUNCTION

  • When the air conditioner switch is turned on, the engine-ECU will receive the A/C ON signal from the switch. The engine-ECU uses this signal to control the A/C compressor relay.

PROBABLE CAUSES

  • Failed A/C switch of heater control unit
  • 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 76: 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. Check the A/C switch of the heater control unit.

  • Check the A/C switch (Refer to GROUP 55A - Heater Control Unit - Air Conditioner Switch Continuity Check ).

Q. Is the check result normal?
Go to Step 3.
Replace the heater control unit.

STEP 3. Perform voltage measurement at heater control unit connector

  • 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 5.
Go to Step 4.

STEP 4. 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 5. Check of open circuit, short circuit, and damage in earth line between heater control unit connector and body earth.

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 heater control unit connector and engine-ECU connector.

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

STEP 7. M.U.T.-III data list

  • Data list reference table (Refer to ).

    1. Item 76: 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.