Mitsubishi Galant (2004+). Manual - part 766

MANUAL A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-203

STEP 16. Measure the voltage at A/C-ECU connector C-15. 

(1) Disconnect A/C-ECU connector C-15 and measure the 

voltage at the relay box side.

(2) Disconnect powertrain control module connector B-21 and 

ground harness side terminal No.81.

(3) Turn the ignition switch to the "ON" position.

AC305233

CONNECTOR: C-15

BG

C-105 (B)

HARNESS SIDE

AC305216

B-21 (B)

AC

CONNECTOR: B-21 <2.4L>

HARNESS SIDE

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AC305229

B-21 (B)

AB

HARNESS SIDE

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CONNECTOR: B-21 <3.8 L>

AC306468

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AC306468

CONNECTOR B-21 
(HARNESS SIDE)

AD

MANUAL A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-204

(4) Measure the voltage between A/C-ECU connector C-15 

terminal No.10 and ground.

• The measured value should be approximately 12 volts 

(battery positive voltage).

Q: Does the measured voltage correspond with this range?

YES : Go to Step 18.
NO :   Go to Step 17.

STEP 17. Check the wiring harness between A/C 
compressor clutch relay connector B-18X (terminal 4) and 

A/C-ECU connector C-15 (terminal 10).

AC209365HI

CONNECTOR C-15 
(HARNESS SIDE)

AC305977AJ

CONNECTOR: B-18X

RELAY BOX SIDE

FRONT OF 
VEHICLE

JUNCTION BLOCK 
TRIANGLE MARK

AC305234

C-15 (B)

C-23

C-15

HARNESS SIDE

C-23

AP

CONNECTORS: C-15, C-23

MANUAL A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-205

NOTE: Also check intermediate connectors A-13 and C-23 for 
loose, corroded, or damaged terminals, or terminals pushed 
back in the connector. If intermediate connector A-13 or C-23 is 
damaged, repair or replace the connector as described in 
GROUP 00E, Harness Connector Inspection 

P.00E-2

.

Q: Is the wiring harness between A/C compressor clutch 

relay connector B-18X (terminal 4) and A/C-ECU 
connector C-15 (terminal 10) in good condition?
YES : It can be assumed that this malfunction is intermittent. 

Refer to GROUP 00, How to Use 
Troubleshooting/Inspection Service Points 

P.00-6

.

NO :  Repair the wiring harness. Check that the air 

conditioning works normally.

STEP 18. 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.

(2) When the oil temperature reaches the standard value, 

check that voltage is supplied between the terminals.

Standard value: 

NOTE: When the oil temperature is 155

°

C (311

°

F) or more 

and there is no continuity, the resistance will not be 2

Ω

 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 19.
NO :  Replace the refrigerant temperature switch. Check 

that the air conditioning works normally.

AC305210

A-13 (GR)

AR

CONNECTOR: A-13

ITEM

TEMPERATURE

Less than 2 ohms Slightly below 155

°C (311°F)

No continuity

155

°C (311°F) or more

AC100787

THERMOMETER

ENGINE OIL

AB

AC100810

LESS THAN 2

Ω 

NO CONTINUITY

125˚C 
(257˚F)

155˚C 
(311˚F)

OIL TEMPRATURE

AE

MANUAL A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-206

STEP 19. Check the air conditioning 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 air conditioning com-
pressor clutch should make a definite operating sound.
Q: Can the sound (click) of the air conditioning 

compressor clutch operation be heard?
YES : Go to Step 20.
NO :  Replace the compressor magnet clutch. Check that 

the air conditioning works normally. 

STEP 20. Check the air thermo sensor.

Measure the resistance between connector terminals 1 and 2 
under at least two different temperatures. The resistance val-
ues should generally match those in the graph. 
NOTE: The temperature at the check should not exceed the 
range in the graph. 
Q: Is the air thermo sensor in good condition?

YES : Go to Step 21.
NO :  Replace the air thermo sensor. Check that the air 

conditioning works normally.

STEP 21. Check the ambient air temperature sensor.

Measure the resistance between the sensor terminals under at 
least two temperatures. The resistance values should meet the 
values shown.
NOTE: The temperature should be within the shown range.
Q: Is the ambient air temperature sensor in good 

condition?
YES : Go to Step 22.
NO :  Replace the ambient air temperature sensor. Check 

that the air conditioning works normally.

AC206292AB

A/C COMPRESSOR 
CLUTCH 
CONNECTOR

AC001043

RESISTANCE k

Ω

8

6

4

2

0

-10

0

 10

 20

 30

   40

TEMPERATURE ˚C(˚F)

AB

(14)

(32)

(50)

(86)

(104)

(68)

AC209942AB

REGISTANCE 
k

Ω

10

20

30

40

0

0

20

(32) (68)

TEMPERATURE ˚C (˚F)

40

(104)

60

(140)

-20

(-4)

-30

(-22)