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 (terminals No. 45) PCM (terminals No. 83) from the automatic compressor controller.

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 connector C-49, C-53 at ECM or connector C-50, C-57 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-49 or PCM connector C-50 .

1. Disconnect the connectors C-49 or C-50 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-53 or PCM connector C-57 .

1. Disconnect the connectors C-53 or C-57 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 voltage normal?

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.