Inspection Procedure 24: A/C Switch System <Cooler, Manual 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 switch terminal on the heater control panel connector.
  • It is earthed from the A/C switch terminal on the heater control panel connector through the blower switch to vehicle body.

FUNCTION

  • When the A/C switch is turned on and the blower switch is not turned off with the dual pressure switch ON conditions satisfied, the A/C switch ON signal is sent to the engine-ECU. The engine-ECU uses this signal to control the A/C compressor relay.

PROBABLE CAUSES

  • Failed A/C switch of heater control unit
  • Failed blower switch of heater control unit
  • Failed dual pressure switch
  • 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 the A/C switch of the heater control unit.

  • Check the A/C switch (Refer to GROUP 55A - Heater Control Unit - Inspection ).

Q. Is the check result normal?
Go to Step 6.
Replace the heater control unit.

STEP 6. Check the blower switch of the heater control unit.

  • Check the blower switch (Refer to GROUP 55A - Heater Control Unit - Inspection ).

Q. Is the check result normal?
Go to Step 7.
Replace the heater control unit.

STEP 7. Check of open circuit, short circuit, and damage in A/C switch signal line between dual pressure switch connector and heater control panel connector.

Q. Is the check result normal?
Go to Step 8.
Repair the connector(s) or wiring harness.

STEP 8. Check of open circuit, short circuit, and damage in A/C switch earth line between heater control panel connector and blower switch connector.

Q. Is the check result normal?
Go to Step 9.
Repair the connector(s) or wiring harness.

STEP 9. Check of open circuit, short circuit, and damage in earth line between blower switch connector and body earth.

Q. Is the check result normal?
Go to Step 10.
Repair the connector(s) or wiring harness.

STEP 10. Check of damage in AC/S line between dual pressure switch and engine-ECU connector.

Q. Is the check result normal?
Go to Step 11.
Repair the connector(s) or wiring harness.

STEP 11. 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.