Inspection Procedure 18: A/C Compressor Relay System

OPERATION

The battery voltage is applied to the A/C compressor relay connector terminal.
The engine-ECU connector terminal AC/R makes the power transistor in the unit be in ON position and makes currents go on the A/C compressor relay coil, and that makes the relay be in ON position.
When the A/C compressor is in ON position, the battery voltage is supplied to the A/C compressor connector terminal from the A/C compressor relay assembly connector terminal.

FUNCTION

When the A/C switch ON signal is input to the engine-ECU, the engine-ECU places the A/C compressor relay in the ON position. Accordingly, the battery voltage supplied to the A/C compressor operates the magnet clutch.

PROBABLE CAUSE

Failed A/C compressor relay
Failed A/C compressor clutch
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.

Check A/C compressor relay (Refer to GROUP 55 - On-vehicle Service - Relay Check ).

Q. Is the check result normal?

	Go to Step 2.

	Replace the A/C compressor relay.

STEP 2. Voltage measurement at A/C compressor relay connector (power supply lines).

(1)Remove relay, and measure at the relay box side.

(2)Check the voltage between the A/C compressor connector (power supply lines) and body earth.
OK: System voltage

Q. Is the check result normal?

	Go to Step 3.

	Repair power supply lines line between battery and A/C compressor relay connector.

STEP 3. Voltage measurement at engine-ECU connector (AC/R terminal).

(1)Disconnect the connector, and measure at the wiring harness side.

(2)Check the voltage between the engine-ECU connector (AC/R terminal) and body earth.
OK: System voltage

Q. Is the check result normal?

	Go to Step 4.

	Repair AC/R line between A/C compressor relay connector and engine-ECU connector.

STEP 4. Voltage measurement at A/C compressor assembly connector (output line).

(1)Disconnect the connector, and measure at the wiring harness side.

(2)Using a jumper wire, connect engine-ECU connector terminal AC/R and body earth.

(3)Check the voltage between the A/C compressor connector (output line) and body earth.
OK: System voltage

Q. Is the check result normal?

	Go to Step 7.

	Go to Step 5.

STEP 5. Check of open circuit and short to earth in output line between A/C compressor relay connector and A/C compressor assembly connector.

Q. Is the check result normal?

	Go to Step 6.

	Repair the connector(s) or wiring harness.

STEP 6. Check of damage in AC/R line between A/C compressor relay connector and engine-ECU connector.

Q. Is the check result normal?

	Repair power supply between battery and A/C compressor relay connector.

	Repair the connector(s) or wiring harness.

STEP 7. Check of damage in power supply line between battery and A/C compressor relay connector.

Q. Is the check result normal?

	Go to Step 8.

	Repair the connector(s) or wiring harness.

STEP 8. Check of damage in output line between A/C compressor relay connector and A/C compressor assembly connector.

Q. Is the check result normal?

	Go to Step 9.

	Repair the connector(s) or wiring harness.

STEP 9. Voltage measurement at engine-ECU connector (AC/R terminal).

(1)Disconnect engine-ECU harness, and connect special tool power plant ECU check harness (MB992291) to measure at connector for inspection.

(2)Engine: Idle operation after warm-up

(3)A/C set temperature:

(4)Voltage measurement at engine-ECU connector (AC/R terminal) and body earth.
OK:
1.0 V or less (when A/C is ON)
System voltage (when A/C is OFF)

Q. Is the check result normal?

	Go to Step 10.

	Replace the engine-ECU.

STEP 10. M.U.T.-III actuator test.

Refer to Actuator Test Reference Table .

Item 4: A/C compressor relay

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 A/C compressor relay.