INSPECTION PROCEDURE 3: The Compressor does not Work: Diagnosis

Required Special Tools: 

• MB991223: Harness Set
• MB992006: Extra Fine Probe
• MB991658: Test Harness Set
• MB991958: Scan Tool (M.U.T.-III Sub Assembly)
  • MB991824: V.C.I.
  • MB991827: M.U.T.-III USB Cable
  • MB991910: M.U.T.-III Main Harness A

1. STEP 1. Using scan tool MB991958, diagnose the CAN bus line. 
   CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
   1. Connect scan tool MB991958. Refer to "HOW TO CONNECT THE SCAN TOOL (M.U.T.-III)  ".
   2. Turn the ignition switch to the "ON" position.
   3. Diagnose the CAN bus line.
   4. Turn the ignition switch to the "LOCK" (OFF) position.

   Q: Is the CAN bus line found to be normal? 

   YES  : Go to Step 2.

   NO  : Repair the CAN bus lines (Refer to PRECAUTIONS ON HOW TO REPAIR THE CAN BUS LINES ).

   Fig 1: Connecting Special Tool To Data Link Connector

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
2. STEP 2. Using scan tool MB991958, read the diagnostic trouble code. 

   Check if an A/C-ECU DTC is set.

   1. Connect scan tool MB991958 to the data link connector.
   2. Turn the ignition switch to the "ON" position.
   3. Check if the DTC is set.
   4. Turn the ignition switch to the "LOCK" (OFF) position.

   Q: Is the DTC set? 

   YES  : Refer to DIAGNOSTIC TROUBLE CODE CHART  .

   NO  : Go to Step 3.

3. STEP 3. Check A/C compressor assembly connector B-110 for loose, corroded or damaged terminals, or terminals pushed back in the connector. 

   Q: Is A/C compressor assembly connector B-110 in good condition? 

   YES  : Go to Step 4.

   NO  : Repair or replace the connector. Refer to HARNESS CONNECTOR INSPECTION .

4. STEP 4. Check the A/C compressor clutch operation. 

   Connect the compressor connector terminal to the battery positive (+) terminal and ground the battery's negative (-) terminal to the compressor unit. At that time, the A/C compressor clutch should make a definite operating sound.

   Q: Can the sound (click) of the A/C compressor clutch operation be heard? 

   YES  : Go to Step 5.

   NO  : Replace the compressor magnet clutch.

   Fig 2: Connecting Compressor Connector Terminal To Battery

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
5. STEP 5. Check A/C compressor clutch relay connector A-17X for loose, corroded or damaged terminals, or terminals pushed back in the connector. 

   Q: Is A/C compressor clutch relay connector A-17X in good condition? 

   YES  : Go to Step 6.

   NO  : Repair or replace the connector. Refer to HARNESS CONNECTOR INSPECTION .

6. STEP 6. Check the A/C compressor clutch relay continuity. 

   Follow the table below to check the A/C compressor clutch relay for continuity.

   A/C COMPRESSOR CLUTCH RELAY CONTINUITY CHECK
   
   

   Battery voltage	Tester connection	Specified condition
   Not applied	3 - 4	Open circuit
   Connect terminal 2 to the positive battery terminal Connect terminal 1 to the negative battery terminal	3 - 4	Less than 2 ohms

   Fig 3: Identifying A/C Compressor Clutch Relay Terminals

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

   Q: Is the A/C compressor clutch relay in good condition? 

   YES  : Go to Step 7.

   NO  : Replace the A/C compressor clutch relay.

7. STEP 7. Check engine control module connector B-10 for loose, corroded or damaged terminals, or terminals pushed back in the connector. 

   Q: Is engine control module connector B-10 in good condition? 

   YES  : Go to Step 8.

   NO  : Repair or replace the connector. Refer to HARNESS CONNECTOR INSPECTION .

8. STEP 8. Measure the voltage at A/C compressor assembly connector B-10. 
   1. Disconnect A/C compressor assembly connector B-10 and measure the voltage at the wiring harness side.
   2. Disconnect engine control module connector B-10 and ground harness side terminal No. 102.
   3. Turn the ignition switch to the "ON" position.
   4. A/C compressor assembly connector B-110 terminal 1 and ground.
      • The measured value should be approximately 12 volts (battery positive voltage).

   Q: Is the measured voltage approximately 12 volts? 

   YES  : Go to Step  13.

   NO  : Go to Step 9.

   Fig 4: Measuring Voltage At A/C Compressor Assembly Connector B-10

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
9. STEP 9. Measure the voltage at A/C compressor clutch relay connector A-17X. 
   1. Disconnect A/C compressor connector A-17X and measure the voltage at the relay box side.
   2. Turn the ignition switch to the "ON" position.
   3. Measure the voltage between terminal 4 and ground.
      • The measured value should be approximately 12 volts (battery positive voltage).
   4. Measure the voltage between terminal 2 and ground.
      • The measured value should be approximately 12 volts (battery positive voltage).
        Fig 5: Measuring Voltage Between Terminal 4 And Ground

        Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

   Q: Is the measured voltage approximately 12 volts? 

   YES  : Go to Step  11.

   NO  : Go to Step 10.

10. STEP 10. Check the wiring harness between A/C compressor clutch relay connector A-17X (terminals 2 and 4) and the fusible link (36). 

    Q: Is the wiring harness between A/C compressor clutch relay connector A-17X (terminals 2 and 4) and the fusible link (36) in good condition? 

    YES  : It can be assumed that this malfunction is intermittent. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS .

    NO  : Repair the wiring harness. Check that the A/C works normally.

11. STEP 11. Check the wiring harness between A/C compressor clutch relay connector A-17X (terminal 3) and A/C compressor assembly connector B-110 (terminal 1). 

    Q: Is the wiring harness between A/C compressor clutch relay connector A-17X (terminal 3) and A/C compressor assembly connector B-110 (terminal 1) in good condition? 

    YES  : Go to Step 12.

    NO  : Repair the wiring harness. Check that the A/C works normally.

12. STEP 12. Check the wiring harness between engine control module connector B-10 (terminal 102) and A/C compressor clutch relay connector A-17X (terminal 1). 

    Q: Is the wiring harness between engine control module connector B-10 (terminal 102) and A/C compressor clutch relay connector A-17X (terminal 1) in good condition? 

    YES  : It can be assumed that this malfunction is intermittent. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTIONS .

    NO  : Repair the wiring harness. Check that the A/C works normally.

13. STEP 13. Check the refrigerant temperature switch. 
    CAUTION: Do not heat more than necessary.
    1. Dip the metal part of the cooling temperature switch into engine oil and increase the oil temperature using a gas burner or similar.
       Fig 6: Checking Resistance Refrigerant Temperature Switch Terminals

       Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
    2. When the oil temperature reaches the standard value, check that resistance is supplied between the terminals.

       Standard value: 

       OIL TEMPERATURE CHART
       
       

       Item	Temperature
       Less than 2 ohms	Slightly below 155°C (311°F)
       No continuity	155°C (311°F) or more

       Fig 7: Oil Temperature Continuity Graph

       Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
       NOTE: When the oil temperature is 155°C (311°F) or more and there is no continuity, the resistance will not be 2Ω or lower until the oil temperature reduces to 125°C (257°F) or less.

    Q: Is the refrigerant temperature switch operating properly? 

    YES  : Go to Step 14.

    NO  : Replace the refrigerant temperature switch. Check that the A/C works normally.

14. STEP 14. Replace the A/C-ECU. 

    Q: Does the A/C operate normally? 

    YES  : No action is necessary and testing is complete.

    NO  : Replace the engine control module. Check that the A/C works normally.