Inspection Procedure 35

A/C Circuit:

CIRCUIT OPERATION
- When the A/C is ON, the battery positive voltage is applied on the ECM (terminal 45) or PCM (terminal 83) from the Automatic Compressor 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.
- Malfunction of the PCM.

DIAGNOSIS

STEP 1. Check circuit at ECM connector C-49, C-53 or PCM connector C-50, C-53 .
1. Disconnect connectors C-49, C-53 or C-50, C-57 and measure at the harness side.
2. Turn the ignition switch to "ON" position.
3. Measure the voltage between terminals 8 (C-49) or 20 (C-50) and ground.
- Voltage should be approximately 12 volts (battery positive voltage).

4. Measure the voltage between terminals 45 (C-53) or 83 (C-57) and ground.
- Voltage should be from 0 to 3 volts when the A/C switch is OFF.
- Voltage should be approximately 12 volts (battery positive voltage) when the A/C switch is ON.

5. Using a jumper wire, connector terminal 8 (C-49) or 20 (C-50) to the ground.
- A/C compressor should turn ON.

6. Turn the A/C switch OFF.
7. Turn the ignition switch to "LOCK" (OFF) position. If the checks above meet the specifications, go to Step 2. If the checks above do not meet the specifications, check the A/C system. Refer to Heater, Air Conditioning and Ventilation Diagnosis - Introduction to Heater, Air Conditioning and Ventilation Diagnosis.
Then check that the malfunction is eliminated.

STEP 2. Check harness connectors C49, C-53 at the ECM or harness connectors C-50, C-57 at the PCM for damage.
If harness connectors C-49, C-53 or C-50, C-57 are in good condition, replace the ECM or PCM.

If harness connectors C-49, C-53 or C-50, C-57 are damaged, repair or replace them.
Refer to Harness Connector Inspection.
Then confirm that the malfunction is eliminated.