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Inspection procedure 28: 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 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 relay circuit, harness damage, or connector damage.
  • ECM failed.

 
 
DIAGNOSIS
STEP 1. Check the circuit at ECM harness side connector.
(1) Disconnect the ECM connectors and measure at the harness side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal AC/R and ground.
  • Voltage should be battery positive voltage.
(4) Using a jumper wire, connect terminal AC/R to ground.
  • A/C compressor clutch relay should turn "ON".
(5) Turn the ignition switch to the "LOCK" (OFF) position.
Is the voltage and A/C compressor relay condition normal?
Replace the ECM (Refer to Removal and Installation ). Then confirm that the malfunction symptom is eliminated.
: Refer to GROUP 55, Automatic A/C Diagnosis - Introduction . Then confirm that the malfunction symptom is eliminated.