Inspection Procedure 34

A/C system

A/C Circuit:

COMMENT
- When the A/C is "ON", the battery positive voltage is applied on the ECM or PCM (terminal No.69) from the A/C-ECU.

When battery positive voltage is applied to the ECM or PCM , the ECM or PCM turns "ON" the power transistor in the ECM or PCM . The ECM or PCM delays A/C engagement momentarily while it increases idle r/min. Then the A/C compressor clutch relay coil will be energized. With this, the A/C compressor clutch relay turns "ON" and the A/C compressor clutch operates.

TROUBLESHOOTING HINTS (The most likely causes for this case:)
- Malfunction of the A/C control system.
- Malfunction of the A/C switch.
- Improper connector contact, open circuit or short-circuited harness wire.
- ECM failed.
- PCM failed.

DIAGNOSIS

STEP 1. Check harness connector C-133, C-137 at ECM or C-134, C-138 at PCM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 2.

NO: Repair or replace it. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.

STEP 2. Check the circuit at ECM connector C-133 or PCM connector C-134 .

1. Disconnect the connector C-133 or C-134 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.

3. Measure the voltage between terminal No.16 and ground.
- Voltage should be battery positive voltage.

4. Using a jumper wire, connect terminal No.16 to ground.
- A/C compressor relay should turn "ON".

5. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Are the measured voltage and A/C compressor relay condition normal?

YES: Go to Step 3.

NO: Refer to Heating and air conditioning - Introduction To Heater, Air Conditioning And Ventilation Diagnosis. Then confirm that the malfunction symptom is eliminated.

STEP 3. Check the voltage at ECM connector C-137 or PCM connector C-138 .

1. Disconnect the connector C-137 or C-138 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.

3. Measure the voltage between terminal No.69 and ground.
- Voltage should be 1 volt or less when the A/C switch is "OFF".
- Voltage should be battery positive voltage when the A/C switch is "ON".

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage within the specified range?

YES: Replace the ECM or PCM. Then confirm that the malfunction symptom is eliminated.

NO: Refer to Heating and air conditioning - Introduction To Heater, Air Conditioning And Ventilation Diagnosis.