Inspection Procedure 21: Poor A/C Performance


COMMENT ON TROUBLE SYMPTOM



PROBABLE CAUSES



DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III diagnosis code

Q. Diagnosis code set?
Inspection chart for diagnosis code (Refer to ).
Go to Step 2 .

STEP 2. A/C compressor magnet clutch operation check.

  • Engine: Idling
  • A/C set temperature:

      • Maximum Cool when temperature in cabin is 25°C or more
      Maximum Hot when temperature in cabin is 25°C or less
OK:
    Magnet clutch active (when A/C is ON)
    Magnet clutch inactive (when A/C is OFF)

Q. Is the check result normal?
Go to Step 4 .
Go to Step 3 .

STEP 3. Perform voltage measurement at A-08 engine-ECU connector.


  • Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector.
  • Engine: Running at idle
  • A/C set temperature:

      • Maximum Cool when temperature in cabin is 25°C or more.
      Maximum Hot when temperature in cabin is 25°C or less.
  • Voltage between terminal No. 39 and earth.
OK:
    Voltage decreases (turn the A/C switch ON)
    System voltage (turn the A/C switch OFF)

Q. Is the check result normal?

Check A/C system (Refer to GROUP 55B - Troubleshooting - Check Chart for Diagnosis Codes ).

Check A/C compressor relay system (Refer to Inspection Procedure 31 ).

STEP 4. Check charged amount of A/C refrigerant.

  • Check charged amount of A/C refrigerant (Refer to GROUP 55B - On-vehicle Service - Sight Glass Refrigerant Level Test ).

Q. Is the check result normal?
Check A/C system (Refer to GROUP 55B - Troubleshooting - Check Chart for Diagnosis Codes ).
Adjust charged amount of A/C refrigerant.