Mitsubishi Evolution X. Manual - part 1282

AUTO A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55-79

.

FUNCTION

Compressor that recovers the refrigerant, which evaporated in 
the evaporator and became a high-temperature and high-pres-
sure gas, and turns it into liquid again.

.

PROBABLE CAUSES

• Insufficient refrigerant

• Malfunction of connector.

• Malfunction of the harness (A/C compressor circuit is 

open/shorted to ground)

• Malfunction of the A/C pressure sensor.

• Malfunction of the A/C compressor.

• Malfunction of the A/C compressor clutch relay.

• Malfunction of the A/C-ECU.

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

AC709111

Connector: A-17X

AB

AC709137

Connector: B-10

AB

C-10 (GR)

AC709136

Connector: B-110

AB

C-110 (GR)

AUTO A/C DIAGNOSIS

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HEATER, AIR CONDITIONING AND VENTILATION

55-80

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 con-
necting or disconnecting scan tool MB991958.
(1) Connect scan tool MB991958. Refer to "How to connect the 

Scan Tool (M.U.T.-III) 

P.55-7

."

(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 GROUP 54C, 

precautions on how to repair the CAN bus lines 

P.54C-14

).

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 

P.55-9

.

NO :  Go to Step 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 GROUP 

00E, Harness Connector Inspection 

P.00E-2

.

AC608435

Data link connector

MB991827

MB991824

MB991910

AB

AUTO A/C DIAGNOSIS

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HEATER, AIR CONDITIONING AND VENTILATION

55-81

STEP 4. Check the A/C compressor clutch operation.
Connect the compressor connector terminal to the battery posi-
tive (+) 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. 

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 GROUP 

00E, Harness Connector Inspection 

P.00E-2

.

STEP 6. Check the A/C compressor clutch relay continuity.
Follow the table below to check the A/C compressor clutch 
relay for continuity.

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

YES : Go to Step 7.
NO :  Replace the A/C compressor clutch relay. 

AC506471

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

AC605626

AC609971

AB

4

1

2

3

3

1

4

2

A/C compressor clutch relay

AUTO A/C DIAGNOSIS

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HEATER, AIR CONDITIONING AND VENTILATION

55-82

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 GROUP 

00E, Harness Connector Inspection 

P.00E-2

.

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.

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).

Q: Is the measured voltage approximately 12 volts?

YES :  Go to Step 11.
NO :   Go to Step 10.

AC608254 CM

Connector B-110
(Harness side)

AC608254 CN

Connector A-17X
(Harness side)