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Inspection procedure 26: A/C system

 
 
 
 
CIRCUIT OPERATION
  • When the A/C switch ON signal is input into the ECM, the ECM turns ON the A/C compressor clutch relay. This causes battery positive voltage to be supplied to the A/C compressor and the magnet clutch actuates.
 
 
COMMENT
  • When the A/C is "ON" the ECM turns "ON" the power transistor in the ECM. The ECM delays A/C engagement momentarily while it increases idle speed. 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:)
  • A/C control system failed.
  • Open or shorted A/C compressor clutch relay circuit, harness damage or connector damage.
  • ECM failed.

 
 
DIAGNOSIS
STEP 1. Check harness connector B-27 at ECM for damage.
Is the harness connector in good condition?
Go to Step 2.
Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then confirm that the malfunction symptom is eliminated.
 
STEP 2. Check the circuit at ECM connector B-27.
(1) Disconnect the connector B-27 and measure at the harness side.
(2) Measure the voltage between terminal No. 102 and ground.
  • Voltage should be battery positive voltage.
(3) Short-circuit the terminal No. 102 to the ground.
  • A/C compressor clutch relay should turn "ON".
Is the voltage and A/C compressor clutch relay condition normal?
Replace the ECM (Refer to, Removal and Installation ). Then confirm that the malfunction symptom is eliminated.
Refer to GROUP 55B, A/C Diagnosis - Symptom Chart .