Inspection Procedure 32

A/C Circuit:

CIRCUIT OPERATION
- When the A/C is "ON", the battery positive voltage is applied on the PCM (terminal 83) from the automatic compressor-ECU.

When the battery positive voltage is applied on the PCM, the PCM turns "ON" the power transistor in the Control module. The 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 PCM.

DIAGNOSIS

STEP 1. Check the circuit at the PCM connectors C-89, C-91.
1. Disconnect connectors C-89 and C-91, and measure at the harness side.
2. Turn the ignition switch "ON".




3. Measure the voltage between terminal 20 and ground.

- Voltage should be approximately 12 volts (battery positive voltage).




4. Measure the voltage between terminal 83 and ground.
- Voltage should be from 0 to 3 volt 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, connect terminal 20 to the ground.
- A/C compressor clutch should turn "ON".

6. Turn the A/C switch "OFF".
7. Turn the ignition switch "OFF".

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 Diagnosis. Then check that the malfunction is eliminated.




STEP 2. Check harness connectors C-89 and C-91 at the PCM for damage.
If harness connectors C-89 and C-91 are in good condition, replace the PCM.

If harness connectors C-89 and C-91 are damaged, repair or replace it. Refer to vehicle level Testing and Inspection.

Then check that the malfunction is eliminated.