Inspection Procedure 34

INSPECTION PROCEDURE 34: A/C System

A/C Circuit:

Connectors:

COMMENT
- When the A/C is "ON", the battery positive voltage is applied on the ECM (terminal No.45) PCM (terminal No.83) from the A/C belt lock-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 rpm. 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 functions.

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.
- Malfunction of the ECM or PCM .

DIAGNOSIS

STEP 1. Check connectors C-109, C-113 at ECM or connectors C-110, C-117 at PCM for damage.

Q: Is the 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-109 or PCM connector C-110 .

1. Disconnect the connectors C-109 or C-110 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.

3. Measure the voltage between terminal No.8 or No. 20 and ground.
- Voltage should be battery positive voltage.
4. Using a jumper wire, connect terminal No.8 or No. 20 to ground.
- A/C compressor relay should turn "ON".
5. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the 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 circuit at ECM connector C-113 or PCM connector C-117.

1. Disconnect the connectors C-113 or C-117 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.

3. Measure the voltage between terminal No.45 or No. 83 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.