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 (terminal No.45). PCM (terminal 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 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 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 harness connector C-119, C-121 at ECM or harness connector C-116, C-120 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-121 or PCM connector C-120 .

1. Disconnect the connectors C-121 or C-120 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.

3. Measure the voltage between terminal No.22 or No.21 and ground.
- Voltage should be battery positive voltage.

4. Using a jumper wire, connect terminal No.22 or No.21 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.

STEP 3. Check the circuit at ECM connector C-119 or PCM connector C-116 .

1. Disconnect the connectors C-119 or C-116 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 Heater, Air Conditioning And Ventilation - Manual A/C Diagnosis - Symptom Chart.