2005 MITSUBISHI 380 GROUP-90

AUTO A/C DIAGNOSIS
HEATER, AIR CONDITIONING AND VENTILATION55-64
DTC U1120: Failure Information on Electronic control unit (Related to Engine)
If DTC U1120 is set in the A/C-ECU, diagnose the
CAN main bus line.
Whenever the ECU is replaced, ensure that the
communication circuit is normal.
The engine control system- related DTC may be
set when DTC U1120 is set. (For details refer to
GROUP 00, Intersystem Affiliated DTC Reference
Ta b l e P.00-17.) Diagnose the engine control sys-
tem first when the engine control system- related
DTC is set.
.
TROUBLE JUDGMENT
The A/C-ECU receives engine control sys-
tem-related signal from the Electronic control unit by
the CAN bus lines. If a fail-safe related data is con-
tained in the signal from the Electronic control unit,
DTC U1120 will be stored.
.
TECHNICAL DESCRIPTION (COMMENT)
Current trouble
The wiring harness wire or connectors may have
loose, corroded, or damage terminals, or termi-
nals pushed back in the connector, the Electronic
control unit, or the A/C-ECU may be defective.Past trouble
If DTC U1120 is stored as a past trouble, carry
out diagnosis with particular emphasis on wiring
and connector(s) in the CAN bus line between
the A/C-ECU and the Electronic control unit, and
the power supply system to the Electronic control
unit. If the connectors and wiring are normal, and
obviously the ECU is the cause of the trouble,
replace the ECU. If in doubt, do not replace the
ECU.
NOTE: For a past trouble, you cannot find it by
the diagnostic tool CAN bus diagnostics even if
there is a failure in CAN bus lines. In this case,
refer to GROUP 00, How to Use Troubleshoot-
ing/Inspection Service Points
How to Cope with
Intermittent Malfunctions P.00-14.) and check the
CAN bus lines. You can narrow down the possi-
ble cause of the trouble by referring to the DTC,
which is set regarding the CAN communica-
tion-linked ECUs (Refer to GROUP 54C
Expla-
nation about the diagnostic tool CAN bus
diagnostics P.54C-6).
.
TROUBLESHOOTING HINTS
Malfunction of the A/C-ECU.
Malfunction of the Electronic control unit.
Refer to component locations GROUP-70
Refer to configuration diagrams GROUP-80
Refer to circuit diagrams GROUP-90
DIAGNOSIS
Required Special Tool:
: Diagnostic Tool (MUT-III Sub Assembly)
MB991824: Vehicle Communication Interface (V.C.I.)
MB991827: MUT-III USB Cable
MB991910: MUT-III Main Harness A (Vehicles with CAN
communication system)

AUTO A/C DIAGNOSIS
HEATER, AIR CONDITIONING AND VENTILATION55-69
SYMPTOM PROCEDURES
INSPECTION PROCEDURE 1: When the Ignition Switch is "ON", the A/C does not Operate.
.
TECHNICAL DESCRIPTION (COMMENT)
The blower system or the compressor system may
be defective if there is no cool air coming from the
vents.
.
TROUBLESHOOTING HINTS
Malfunction of blower motor
Malfunction of A/C compressor
Refer to component locations GROUP-70
Refer to configuration diagrams GROUP-80
Refer to circuit diagrams GROUP-90
DIAGNOSIS
Check that the blower motor operation when the blower
switch is moved to the "HI" position.
(1) Turn the ignition switch to the "ON" position.
(2) Turn the blower speed selection dial to the blower operating
position.
Q: Does the blower motor operate when the speed
selection dial is turned to the blower operating
position?
YES : Refer to Inspection procedure 4 "When the A/C is
operating, temperature inside the passenger
compartment does not decrease (cool air not emitted)
P.55-75."
NO : Refer to Inspection procedure 5 "Blower fan and
motor do not turn P.55-89."
INSPECTION PROCEDURE 2: When the Air Outlet Changeover Control Knob is Moved to
DEFROSTER or DEFROSTER/FOOT Position, the A/C or the Inside/outside Air Changeover Damper
Motor does not operate.
.
TECHNICAL DESCRIPTION (COMMENT)
If the outside/inside air selection damper control
motor does not operate normally, the inside/outside
air changeover damper motor system may be defec-
tive.
.
TROUBLESHOOTING HINTS
Malfunction of the A/C-ECU
Malfunction of the outside/inside air selection
damper control motor
Damaged harness wires or connectors
Refer to component locations GROUP-70
Refer to configuration diagrams GROUP-80
Refer to circuit diagrams GROUP-90

AUTO A/C DIAGNOSIS
HEATER, AIR CONDITIONING AND VENTILATION55-70
DIAGNOSIS
Check operation of the outside/inside air selection damper
control motor.
(1) Turn the ignition switch to the "ON" position.
(2) Outside/inside air selection damper motor switch: This is
used to switch from the inside air to outside air or vice
versa.
(3) Check to see that the outside/inside air selection damper
motor operates normally.
Q: Does outside/inside air selection damper control motor
work normally?
YES : Replace the A/C-ECU.
NO : Refer to Inspection procedure 3, "Inside/outside air
changeover is not possible P.55-70."
INSPECTION PROCEDURE 3: Outside/Inside Air Changeover is not possible.
.
CIRCUIT OPERATION
If the outside/inside air selection damper control
motor does not operate normally, the outside/inside
air selection damper control motor system may be
defective.
.
TROUBLESHOOTING HINTS
Malfunction of the outside/inside air selection
damper control motor
Malfunction of the A/C-ECU
Damaged harness wires or connectors
Refer to component locations GROUP-70
Refer to configuration diagrams GROUP-80
Refer to circuit diagrams GROUP-90
DIAGNOSIS
Required Special Tool:
MB991223: Test Harness Set
STEP 1. Check the defogger and A/C operations.
Q: Do the defogger and A/C work normally?
YES : Go to Step 2.
NO : Refer to Inspection procedure 10 "Malfunction of the
A/C-ECU power supply system P.55-122."

AUTO A/C DIAGNOSIS
HEATER, AIR CONDITIONING AND VENTILATION55-75
INSPECTION PROCEDURE 4: When the A/C is Operating, Temperature Inside the Passenger
Compartment does not Decrease (Cool Air is not Emitted).
.
TECHNICAL DESCRIPTION (COMMENT)
If cool air is not distributed when the A/C switch is on,
the A/C compressor relay system may be defective.
.
TROUBLESHOOTING HINTS
Improper amount of refrigerant
Malfunction of the air thermo sensor
Malfunction of the ambient air temperature sen-
sor
Malfunction of the A/C pressure sensor
Malfunction of the A/C compressor relay
Malfunction of the A/C refrigerant temperature
switch
Malfunction of the air conditioning compressor
clutch
Malfunction of the A/C-ECU
Malfunction of the ECU
Damaged harness wires or connectors
Refer to component locations GROUP-70
Refer to configuration diagrams GROUP-80
Refer to circuit diagrams GROUP-90
DIAGNOSIS
Required Special Tools:
MB991223: Harness Set
: Scan Tool (MUT-III Sub Assembly)

AUTO A/C DIAGNOSIS
HEATER, AIR CONDITIONING AND VENTILATION55-89
INSPECTION PROCEDURE 5: Front Blower Fan and Motor do not Turn.
.
CIRCUIT OPERATION
If the blower motor does not operate, the blower
relay system is suspected.
.
TROUBLESHOOTING HINTS
Malfunction of the front blower relay
Malfunction of the power transistor
Malfunction of the front blower motor
Malfunction of the A/C-ECU
Damaged harness wires or connectors
Refer to component locations GROUP-70
Refer to configuration diagrams GROUP-80
Refer to circuit diagrams GROUP-90

AUTO A/C DIAGNOSIS
HEATER, AIR CONDITIONING AND VENTILATION55-100
STEP 17. Replace the power transistor.
Q: Does the blower motor operate normally?
YES : No action is necessary and testing is complete.
NO : Replace the A/C-ECU. Check that the air conditioning
works normally.
INSPECTION PROCEDURE 6: Front Blower Air Amount cannot be Changed.
.
CIRCUIT OPERATION
If the blower motor speed cannot be changed, the
power transistor circuit is suspected.
.
TROUBLESHOOTING HINTS
Malfunction of the power transistor
Malfunction of the front A/C-ECU
Damaged harness wires or connectors
Refer to component locations GROUP-70
Refer to configuration diagrams GROUP-80
Refer to circuit diagrams GROUP-90
DIAGNOSIS
Required Special Tool:
MB991223: Test Harness Set
STEP 1. Check blower power transistor connector C-104
for loose, corroded or damaged terminals, or terminals
pushed back in the connector.
Q: Is power transistor connector C-104 in good condition?
YES : Go to Step 2.
NO : Repair or replace the connector. Refer to GROUP
00E, Harness Connector Inspection P.00E-2.The
blower motor should operate normally.

AUTO A/C DIAGNOSIS
HEATER, AIR CONDITIONING AND VENTILATION55-104
INSPECTION PROCEDURE 7: The A/C Indicator Flashes.
.
TECHNICAL DESCRIPTION (COMMENT)
If the A/C indicator flashes, inadequate refrigerant
quantity, the ambient air temperature sensor circuit
or the A/C pressure sensor circuit is suspected.
.
TROUBLESHOOTING HINTS
Malfunction of the A/C pressure sensor
Malfunction of the ambient air temperature sen-
sor
Malfunction of the A/C-ECU
Refer to component locations GROUP-70
Refer to configuration diagrams GROUP-80
Refer to circuit diagrams GROUP-90
DIAGNOSIS
Required Special Tools:
MB991223: Test Harness Set
: Scan Tool (MUT-III Sub Assembly)
MB991824: Vehicle Communication Interface (V.C.I.)
MB991827: MUT-III USB Cable
MB991910: MUT-III Main Harness A (Vehicles with CAN
communication system)
STEP 1. Using scan tool , read the diagnostic trouble code.
Check if an A/C-ECU DTC is set.
(1) Connect scan tool 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 check result satisfactory?
YES : Go to Step 2.
NO : Refer to DIAGNOSTIC TROUBLE CODE CHART
P.55-9.

AUTO A/C DIAGNOSIS
HEATER, AIR CONDITIONING AND VENTILATION55-110
INSPECTION PROCEDURE 8: Defogger Function Does Not Operate.
.
TECHNICAL DESCRIPTION (COMMENT)
If the defogger does not operate when the defogger
switch is turned on, the defogger relay system may
be defective.
.
TROUBLESHOOTING HINTS
Malfunction of the A/C-ECU
Malfunction of the defogger relay
Damaged harness wires or connectors
Refer to component locations GROUP-70
Refer to configuration diagrams GROUP-80
Refer to circuit diagrams GROUP-90
DIAGNOSIS
Required Special Tool:
MB991223: Test Harness Set
STEP 1. Check the A/C and outside/inside air selection
damper control motor operation.
Q: Do the A/C and outside/inside air selection damper
control motor work normally?
YES : Go to Step 2.
NO : Refer to Inspection procedure 10, "Malfunction of the
A/C-ECU power supply systemP.55-122."