Mitsubishi Lancer Evolution IX. Manual - part 550

TROUBLESHOOTING

HEATER, AIR CONDITIONER AND VENTILATION

55-73

Inspection Procedure 9: Malfunction of the A/C-ECU power supply system.

CIRCUIT OPERATION

The A/C-ECU power system may be defective if the 
A/C, defogger, and outside/inside air selection 
damper motor all do not operate normally.

PROBABLE CAUSES

• Damaged the wiring harness or connectors

• Malfunction of the A/C-ECU

A/C-ECU Power Supply Circuit

Wire colour code
B : Black     LG : Light green     G : Green     L : Blue     W : White     Y : Yellow     SB : Sky blue
BR : Brown     O : Orange     GR : Grey     R : Red     P : Pink     V : Violet     PU : Purple

IGNITION
SWITCH (IG2)

BATTERY
BACK-UP

A/C-ECU

BATTERY

RELAY
BOX

<LHD>

<RHD>

TROUBLESHOOTING

HEATER, AIR CONDITIONER AND VENTILATION

55-74

DIAGNOSIS PROCEDURE

STEP 1. Voltage measurement at A/C-ECU 
connector C-37.

(1) Disconnect the connector, and measure at the 

wiring harness side.

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

(3) Measure the voltage between terminal 28 and 

body earth.

OK: System voltage

Q: Is the check result normal?

YES : 

 Go to Step 4.

NO : 

 Go to Step 2.

STEP 2. Connector check: C-37 A/C-ECU 
connector

Q:  Is the check result normal?

YES : 

Go to Step 3.

NO : 

Repair the connector.

STEP 3. Check the wiring harness between C-37 
A/C-ECU connector terminal No.28 and the 
ignition switch (IG2).

AC504622AC

Connector: C-37 <LHD>

Harness side

C-37 (B)

AC504618AE

Connector: C-37 <RHD>

Harness side

C-37 (B)

AC301541JV

Connector C-37 
(Harness side)

AC504622AC

Connector: C-37 <LHD>

Harness side

C-37 (B)

AC504618AE

Connector: C-37 <RHD>

Harness side

C-37 (B)

AC504622AC

Connector: C-37 <LHD>

Harness side

C-37 (B)

AC504618AE

Connector: C-37 <RHD>

Harness side

C-37 (B)

TROUBLESHOOTING

HEATER, AIR CONDITIONER AND VENTILATION

55-75

NOTE: 

Prior to the wiring harness inspection, check junction 
block connectors C-214 and C-211, and repair if nec-
essary.

• Check the A/C-ECU power supply line for open or 

short circuit.

Q: Is the check result normal?

YES : 

The trouble can be an intermittent 

malfunction (Refer to GROUP 00, How to 
Cope with Intermittent Malfunction 

P.00-5

).

NO : 

Repair the wiring harness.

STEP 4. Resistance measurement at C-37 
A/C-ECU connector.

(1) Remove the relay, and measure at the junction 

block side.

(2) Continuity between terminal 27 and body earth.

OK: 2 ohm or less

Q: Is the check result normal?

YES : 

Go to Step 7.

NO : 

 Go to Step 5.

AC504633AB

Connectors: C-211, C-214 <LHD>

Harness side

Junction block (Front view)

C-214

C-211

C-211

C-214

AC504635AB

Harness side

C-211

C-211

C-214

C-214

Junction block (Front view)

Connectors: C-211, C-214 <RHD>

AC504622AC

Connector: C-37 <LHD>

Harness side

C-37 (B)

AC504618AE

Connector: C-37 <RHD>

Harness side

C-37 (B)

AC301541JW

Connector C-37
(Harness side)

TROUBLESHOOTING

HEATER, AIR CONDITIONER AND VENTILATION

55-76

STEP 5. Connector check: C-37 A/C-ECU 
connector

Q: Is the check result normal?

YES : 

Go to Step 6.

NO : 

Repair the connector.

STEP 6. Check the wiring harness between C-37 
A/C-ECU connector terminal No.27 and the earth.

NOTE: 

Prior to the wiring harness inspection, check joint 
connector C-06 <LH drive vehicles>, and repair if 
necessary.

• Check the A/C-ECU earth line for open or short 

circuit.

Q: Is the check result normal?

YES : 

Replace the automatic A/C control panel 

(A/C-ECU).

NO : 

Repair the wiring harness.

AC504622AC

Connector: C-37 <LHD>

Harness side

C-37 (B)

AC504618AE

Connector: C-37 <RHD>

Harness side

C-37 (B)

AC504622AC

Connector: C-37 <LHD>

Harness side

C-37 (B)

AC504618AE

Connector: C-37 <RHD>

Harness side

C-37 (B)

AC504617AI

Connector: C-06 <LHD>

C-06 (GR)

AC504625AC

Connector: C-06 <RHD>

C-06 (GR)