Mitsubishi Montero (2002-2004). Manual - part 35

GENERAL DESCRIPTION

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-3

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GENERAL DESCRIPTION

M1551000100080

The heater system uses a two-way-flow full-air-mix 
system that features high performance and low oper-
ating noise. The air conditioning (A/C) system is 
basically the same as the conventional system, but a 
new refrigerant system has been adopted as a 
response to restrictions on the use of chlorofluoro-
carbons.

SAFETY PRECAUTIONS

WARNING

Wear safety goggles when servicing the 
refrigeration system to prevent severe dam-
age to hands.

Because R134a refrigerant is a hydro fluorocarbon 
(HFC) which contains hydrogen atoms in place of 
chlorine atoms, it will not cause damage to the ozone 
layer. Ozone filters out harmful radiation from the 
sun. To assist in protecting the ozone layer, 
Mitsubishi Motors Corporation recommends an 
R134a refrigerant recycling device. Refrigerant 
R134a is transparent and colorless in both the liquid 
and vapor state. Since it has a boiling point of 

− 29.8 

°C(− 21.6 °F) at atmospheric pressure, it will be a 

vapor at all normal temperatures and pressures. The 
vapor is heavier than air, non-flammable, and non-
explosive. The following precautions must be 
observed when handling R134a.

WARNING

Do not heat R134a above 40

°C (104°F) or it 

may catch fire and explode.

R134a evaporates so rapidly at normal atmospheric 
pressures and temperatures that it tends to freeze 
anything it contacts. For this reason, extreme care 
must be taken to prevent any liquid refrigerant from 
contacting the skin and especially the eyes. Always 
wear safety goggles when servicing the refrigeration 
part of the A/C system. Keep a bottle of sterile min-
eral oil handy when working on the refrigeration sys-
tem.
1. Should any liquid refrigerant get into the eyes, use 

a few drops of mineral oil to wash them out. 
R134a is rapidly absorbed by the oil.

2. Next splash the eyes with plenty of cold water.
3. Call your doctor immediately even though irritation 

has ceased after treatment.

CAUTION

Keep R134a containers upright when charging 
the system.
In most instances, moderate heat is required to bring 
the pressure of the refrigerant in its container above 
the pressure of the system when charging or adding 
refrigerant. A bucket or large pan of hot water not 
over 40 

°C (104 °F) is all the heat required for this 

ITEMS

SPECIFICATIONS

Heater unit

Type

Two-way-flow full-air-mix system

Heater control assembly

Dial type

Compressor

Model

10S17C

Dual pressure switch 
kPa (psi)

High-pressure switch ON to OFF: 3,140 (455.5), OFF to ON: 2,550(369.9)
Low-pressure switch ON to OFF: 196 (28.4), OFF to ON: 223 (32.4)

Refrigerant and 
quantity g (oz)

Vehicles without rear 
A/C or rear cooler

R134a (HFC-134a), Approximately 530 

− 570 (18.7 − 20.1)

Vehicles with rear A/
C or rear cooler

R134a (HFC-134a), Approximately 730 

− 770 (26.1 − 27.1)

GENERAL DESCRIPTION

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-4

purpose. Do not heat the refrigerant container with a 
blow torch or any other means that would raise tem-
perature and pressure above this temperature. Do 
not weld or steam clean on or near the system com-
ponents or refrigerant lines.

WARNING

The leak detector for R134a should be used 
to check for refrigerant gas leaks.

CAUTION

Do not allow liquid refrigerant to touch bright 
metal or it will be stained.
When metering R134a into the refrigeration system 
keep the supply tank or cans in an upright position. If 
the refrigerant container is on its side or upside 
down, liquid refrigerant will enter the system and 
damage the compressor. Refrigerant will tarnish 
bright metal and chrome surfaces, and in combina-
tion with moisture can severely corrode all metal sur-
faces.

OPERATION

When the air conditioning is working under low loads 
(e.g, in winter), the PCM controls the A/C compres-
sor, condenser fan and idle-up speed more effec-
tively, resulting in good fuel economy and quiet 
engine operation. In addition, the condenser fan will 
always run for five minutes as initial check after the 
battery is reconnected.

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Condenser fan control
When operating the air conditioning switch

• When the signal which turns on the compressor 

is output from the automatic compressor control-
ler, PCM activates the condenser fan relay and 
rotates the condenser fan.

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Compressor control
When operating the air conditioning switch

• The automatic compressor controller stops the 

compressor when the air thermo sensor detects a 
temperature of 3.2

°C (38°F) or less. However, if 

the ambient air temperature sensor detects a 
temperature of 10 

− 20°C (50 − 68°F), the con-

troller stops the compressor when the air thermo 
sensor detects 6.2

°C (43°F) or less. Because of 

this control, the compressor can work efficiently 
when the air conditioning is under low load.

• The PCM stops the compressor when the engine 

coolant temperature sensor detects 115

°C 

(239

°F). In addition, the compressor stops for five 

seconds when the accelerator position sensor 
input exceeds 80%. Moreover, the compressor 
stops during engine start and low engine speed. 
Because of this control, the engine load can be 
reduced.

• The dual pressure switch turns OFF when the 

refrigerant pressure becomes excessively high or 
low, thus protecting the compressor circuit. (See 
Table below.)

• When these two sensors are all activated, the 

dual pressure switch is ON, and the ignition 
switch, blower switch, and air conditioning switch 
are ON, the A/C compressor relay is energized.

• When operating the air outlet changeover control 

knob

• When the air outlet changeover control knob is 

moved to "DEFROSTER" or "DEFROSTER/
FOOT" position, the micro switch, which is con-
nected in series to the air conditioning switch, is 
turned on. The other compressor control than the 
above is the same as that when operating the air 
conditioning switch.

MANUAL A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-5

A/C Compressor Relay ON Conditions

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MANUAL A/C DIAGNOSIS

INTRODUCTION TO HEATER, AIR CONDITIONING AND VENTILATION DIAGNOSIS

M1552012200269

Air is drawn into the heater assembly from either the 
outside, or from the inside of the passenger cabin if 
DEFROST, maximum cooling or RECIRCULATION 
are selected. The air is then forced through the evap-
orator where heat is removed, cooling and de-humid-
ifying the air. Depending on the temperature 
selected, a portion of this air is then forced through 
the heater core to achieve the selected discharge 
temperature.

If the system does not cool properly, look for a prob-
lem with the refrigerant, blower or air distribution sys-
tems. If the system does not heat properly, look for a 
problem with the coolant, blower or air distribution 
systems fuses, circuit breaker and relays should be 
checked

HEATER, AIR CONDITIONING AND VENTILATION DIAGNOSTIC TROUBLESHOOTING 
STRATEGY

M1552009600289

Use these steps to troubleshoot heater and air condi-
tioning concerns. These diagnostic step are 
designed to systematically check the systems and 
components. Follow these steps carefully, and you 
will be sure that you have exhausted most of the pos-
sible ways to find a heater, air conditioning and venti-
lation fault.

1. Gather information from the customer.
2. Verify that the condition described by the 

customer exists.

3. Find the malfunction by following the Symptom 

Chart.

4. Verify that the malfunction is eliminated and the 

system works properly.

Ignition switch (IG2)

ON

Remarks 
(1) A/C compressor relay is de-energized 
when any one switch, sensor or control 
unit shown on the left turns off (HI). 
(2) *: Automatic compressor controller 
and PCM judges from input signals from 
the sensors.

Blower switch

ON

Air conditioning switch or micro switch

ON

Air thermo sensor

*

Outside air temperature sensor

*

Engine coolant temperature sensor

*

Dual pressure switch 

Low-pressure side 223 kPa 
(32.4 psi) or higher

ON

High-pressure side 2,550 
kPa (369.9 psi) or below

ON

A/C compressor relay driving transistor (within automatic 
compressor controller and engine control module)

ON

MANUAL A/C DIAGNOSIS

TSB Revision

HEATER, AIR CONDITIONING AND VENTILATION

55A-6

SYMPTOM CHART

M1552009900354

NOTE: For symptoms marked with an asterisk the 
condenser fan might not operate when there is an air 
conditioning low load from the air conditioning con-
denser control, so remove the battery terminal (

−

) 

and then check the symptoms 5 minutes after initial 
start control reconnection.

SYMPTOM PROCEDURES

INSPECTION PROCEDURE 1: When the Ignition Switch is "ON," the A/C does not Operate.

DIAGNOSIS

STEP 1. Check for refrigerant leaks.
Q: Is the refrigerant leaking?

YES : Repair the leak. Then go to Step 10.
NO :  Go to Step 2.

STEP 2. Check for excessive refrigerant.
Q: Is the refrigerant in good condition?

YES : Go to Step 3.
NO :  Use the refrigerant recovery station to remove all of 

the refrigerant, and then calculate the amount of the 
refrigerant and charge it. Then go to Step 10.

SYMPTOM

INSPECTION 
PROCEDURE

REFERENCE 
PAGE

When the ignition switch is "ON," the A/C does not operate.

1

P.55A-6

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.

2

P.55A-10

When the A/C is operating, temperature inside the passenger 
compartment does not decrease (cool air is not emitted).

3

P.55A-10

Blower fan and motor does not turn.

4

P.55A-12

Blower fan and motor does not stop turning.

5

P.55A-14

When the A/C is operating condenser fan does not turn.*

6

P.55A-16

Inside/Outside Air changeover is not possible.

7

P.55A-17