Inspection Procedure 34
INSPECTION PROCEDURE 34: A/C SystemA/C Circuit:
COMMENT
- When the A/C is "ON", the battery positive voltage is applied on the ECM (terminal No. 83) from the automatic compressor controller.
When battery positive voltage is applied to the ECM, the ECM turns "ON" the power transistor in the ECM. The ECM 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.
- Malfunction of the ECM.
DIAGNOSIS
STEP 1. Check connector C-117, C-121 at ECM for damage.
Q: Is the connector in good condition?
YES: Go to Step 2.
NO: Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 2. Check the circuit at ECM connector C-121.
1. Disconnect the connectors C-121 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between terminal No. 20 and ground.
- Voltage should measure battery positive voltage.
4. Using a jumper wire, connect terminal 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, Heater, Air Conditioning And Ventilation - Manual A/C Diagnosis - Symptom Chart in heating and Air Conditioning/Testing/Diagnosis By Symptom.
STEP 3. Check the circuit at ECM connector C-117.
1. Disconnect the connectors C-117 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between terminal No. 83 and ground.
- Voltage should measure 1 volt or less when the A/C switch is "OFF".
- Voltage should measure 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. Then confirm that the malfunction symptom is eliminated.
NO: Refer to, Heater, Air Conditioning And Ventilation - Manual A/C Diagnosis - Symptom Chart in heating and Air Conditioning/Testing/Diagnosis By Symptom.