Mitsubishi Lancer (4A9 engine). Manual — part 302

ON-VEHICLE SERVICE

HEATER, AIR CONDITIONER AND VENTILATION

55A-89

DIAGNOSIS BY REFRIGERANT
PRESSURE

M1552023000184

A/C
system
symptom

Measurement circumstance

Cause

Measures

Hig
h
pres
sure

Low
pres
sure

Air
outl
et
tem
pera
ture

Note

Cooler is
not
effective.

Low High High

• Pressure for low

pressure side is high,
and high pressure
side is low.

• When the A/C

operation is stopped,
the pressures of low
pressure side and
high pressure side
immediately become
identical.

• Leakage inside

compressor

• Faulty

compression of
compressor

1. Check according to the

compressor check.
1. When no foreign object

is present to the oil, and
when the colour is light
grey, replace only the
compressor.

2. When foreign objects

are mixed to the oil, and
the colour is black,
replace the compressor
and receiver.

2. Perform the evacuation

sufficiently to remove the
foreign objects and
moisture in the cycle.

3. Fill the new gas to the

specified amount.

High High High

• Low pressure side/

high pressure side
pressure is too high.

• Low pressure side

piping is too hot to
touch.

• Air is mixed to

the refrigerant
cycle.

• Evacuation is

insufficient.

1. Perform the evacuation

sufficiently, and remove
the foreign objects and
moisture in the cycle.

2. Fill the new gas to the

specified amount.

Sufficient
cooling and
insufficient
cooling
occur
periodically.

Fluc
tuati
on

Fluc
tuati
on

Fluc
tuati
on

During the air
conditioner operation,
the low pressure side
pressure alternates
between the negative
pressure and normal.
(also in the high
pressure side, the
abnormal and normal
statuses are alternated).

The moisture in
the refrigerant
cycle becomes
frozen in the
expansion valve,
then the
circulation of
refrigerant is
stopped
temporarily.
Subsequently, the
status recovers to
normal by the
melting of ice.

1. Replace the receiver

(drier).

2. Perform the evacuation

sufficiently, and remove
the moisture in the cycle.

3. Fill the new refrigerant to

the specified amount.

ON-VEHICLE SERVICE

HEATER, AIR CONDITIONER AND VENTILATION

55A-90

Cooler is
sometimes
not
effective.
(works
occasionall
y)

Low Vac

uum

Fluc
tuati
on

• The low pressure

side pressure
indicates the
vacuum, and the high
pressure side
indicates the low
pressure.

• To the piping before

and after the
expansion valve,
frost or dew is
observed.

• The foreign

objects or
moisture inside
the refrigerant
cycle deposits
or
freezes inside
the expansion
valve, and the
refrigerant flow
is disturbed.

• Because of the

expansion
valve operation
failure, the
refrigerant flow
is disturbed.

1. Check the expansion

valve.
1. If foreign objects are

present inside the
expansion valve,
remove them by using
an air gun or others.

2. When no foreign object

is present, the
expansion valve
operation failure is
suspected. Therefore,
replace the expansion
valve.

2. Perform the evacuation

sufficiently, and remove
the foreign objects and
moisture in the cycle.

3. Fill the new refrigerant to

the specified amount.

A/C
system
symptom

Measurement circumstance

Cause

Measures

Hig
h
pres
sure

Low
pres
sure

Air
outl
et
tem
pera
ture

Note

ON-VEHICLE SERVICE

HEATER, AIR CONDITIONER AND VENTILATION

55A-91

Cooling
effectivene
ss is bad.

Low Low Slig

htly
high

• Low pressure side/

high pressure side
pressure is low.

• Outlet air

temperature is high.

• Gas leakage is

present to
somewhere in
the refrigerant
cycle.

• Refrigerant gas

amount is
insufficient.

1. When the pressure gauge

indication is close to zero,
check the leak position,
and then repair the
leakage. Also, when the
value is lower than the
standard pressure, check if
the gas leakage is present,
and repair if necessary.

2. After checking the leak

position, sufficiently
perform the evacuation,
then fill the new gas to the
specified amount.

High High Slig

htly
high

Low pressure side/high
pressure side pressure
is too high.

• Refrigerant

amount is
excessive.

• Condenser

cooling is
insufficient.

1. Clean the condenser fin

(fouling, fin clogging)

2. Check the condenser fan

motor (radiator fan)
operation.

3. When 1 and 2 are normal,

recover all the refrigerant.
Then, perform a sufficient
evacuation again, and fill
the new gas to the
specified amount.

High High High

• Low pressure side/

high pressure side
pressure is too high.

• Frost or dew is

formed to the low
pressure side.

Expansion valve
trouble (valve
opened
excessively)

Replace the expansion valve.

Nor
mal

Nor
mal

Slig
htly
high

-

Because of the
slight difference of
measurement
environment,
secular change of
vehicle, or others,
it is possible that
the outlet
temperature
fluctuation has
occurred.

Check the status for a while,
and if the status does not
improve, recover all the
refrigerant, then fill to the
appropriate amount.

A/C
system
symptom

Measurement circumstance

Cause

Measures

Hig
h
pres
sure

Low
pres
sure

Air
outl
et
tem
pera
ture

Note

ON-VEHICLE SERVICE

HEATER, AIR CONDITIONER AND VENTILATION

55A-92

COMPRESSOR CHECK

Trouble
symptom

Check method/
circumstance

Cause

Measures

Abnormal
noise from
compressor
main body at
A/C operation
(rattling
noise)

• Refrigerant cycle gauge

pressure check
1. Low pressure side/high

pressure side pressure
is high.

2. Pressure hunting

occurs.

Abnormal noise due to
excessive refrigerant
charging

Fill an appropriate amount of
refrigerant.

• Check the refrigerant

cycle gauge pressure.
When the pressure
difference between the
low pressure side and
high pressure side is
small, remove the
compressor oil, and
perform the oil judgment.

Damage to inside the
compressor

AC610320

Compressor oil judgment result:
Between transparent and grey/
No contamination with foreign materials

Measures: Replace only the compressor.

Measures: Replace the compressor and the rece

Compressor oil judgment result:
Between grey and black/
Contaminated with foreign materials

AB

Compressor
malfunction
(belt slip)

Check the compressor
rotation, and if a seizure or
sticking is present, remove
the compressor oil, then
perform a judgment.

SIMPLE INSPECTION OF THE A/C
PRESSURE SENSOR

M1552014700561

1. Assemble a gauge manifold on the high pressure

service valve.

AC609413

A/C pressure sensor

AC

AC507502

MB991658

AB

A/C
pressure
sensor side

Harness side

2. Disconnect the A/C pressure sensor connector

and connect the special tool test harness
(MB991658) as shown.