Inspection Procedure 21: A/C Compressor Relay System

OPERATION

Battery voltage is applied to the A/C compressor relay connector terminal.
Engine-ECU connector terminal AC/R applies current to the A/C compressor relay coil by turning ON the power transistor in the unit in order to turn the relay ON.
When the A/C compressor relay turns ON, battery voltage is supplied by the A/C compressor relay connector terminal to the A/C compressor connector terminal.

FUNCTION

When the A/C switch ON signal is input into the engine-ECU, the engine-ECU turns ON the A/C compressor relay. This causes battery voltage to be supplied to the A/C compressor assembly and the A/C compressor clutch actuates.

PROBABLE CAUSES

Failed A/C compressor relay
Failed A/C compressor assembly
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 itself.

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

Q. Is the check result normal?

	Go to Step 2.

	Repair or replace the connector or replace the A/C compressor relay.

STEP 2. Perform voltage measurement at A/C compressor relay.

Disconnect relay, and measure at relay box side.
Voltage between terminal power supply lines and body earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 3.

	Check and repair harness between battery and A/C compressor relay connector terminals. Check power supply line for open/short circuit.

STEP 3. Check harness between battery and A/C compressor relay connector terminal.

Check power supply line for damage.

Q. Is the check result normal?

	Go to Step 4.

	Repair the damaged harness wire.

STEP 4. Perform voltage measurement at engine-ECU connector.

Disconnect connector, and measure at harness side.
Voltage between terminal AC/R and body earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 5.

	Repair or replace the connector, or check and repair harness between A/C compressor relay connector terminal and engine-ECU connector terminal AC/R. Check signal line for open/short circuit.

STEP 5. Check harness between A/C compressor relay connector terminal and engine-ECU connector terminal AC/R.

Check signal line for damage.

Q. Is the check result normal?

	Go to Step 6.

	Repair the damaged harness wire.

STEP 6. Check harness between A/C compressor relay connector terminal and A/C compressor assembly connector terminal.

Check power supply line for open/short circuit and damage.

Q. Is the check result normal?

	Go to Step 7.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 7. Check A/C compressor clutch operating conditions.

Disconnect engine-ECU connector, and short-circuit terminal AC/R to the body earth.

OK: A/C compressor clutch operates.

Q. Is the check result normal?

	Replace the engine-ECU.

	Replace the A/C compressor assembly.