Inspection Procedure 24: A/C Switch System

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 A/C-ECU
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 ).

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. 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 ).

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.