313

Section 7 A/C System Faults Check & Troubleshooting

I. A/C System Faults Check

Inspection shall be made to isolate the fault area and its cause when the fault of A/C system occurs, and then

specific service could be performed. Inspect the whole system before re-using A/C system after a long term

of storage.

First step is initial inspection by direct "see, listen and touch". Test the system with the leak detector if

necessary.

1. Check the Refrigeration System

Under the normal condition, the low pressure pipeline of the A/C refrigeration system takes on a status of low

temperature and the high pressure pipeline takes on a status of high temperature, see Figure 16. Based on

this rule, you can arrive at the initial judgement about the fault area and its cause by touching the refrigeration

system pipeline and elements to feel the surface temperature with your hand.

1

High pressure area: compressor outlet 

condenser  receiver/drier

 expansion valve

inlet, its temperature change trend is from warm

to hot. If the temperature change is not this trend,

but instead some part is extremely hot (e.g.

condenser surface), it indcates that the part is

faulty and the radiation is not good; if some part is

extremely cold (e.g. receiver/drier) or there is frost

(e.g. at expansion valve inlet), it indicates that the

part is faulty and the pipe may be blocked.

2

Low pressure area: expansion valve outlet 

evaporator 

 compressor inlet, its temperature

change trend is from cool to cold, If the

temperature change is not this trend, it indcates that the part is faulty.

3

Compressor: compressor inlet and outlet high & low side shall have apparent feel of temperature difference,

if there is no temperature difference, it indicates that there is leakage in the system and the refrigerant

has leaked.

2. Check the Leakage Area

1

Observe all connecting areas of the refrigeration system or condenser surface for oil stain, if there is oil

stain, it indicates that the the refrigerant is leaking (refrigerant and freezing oil leak simultaneously,

refrigerant volatilize after leakage and leave the freezing oil remained to be oil stain).

2

Apply the soap water to the connecting area, if soap bubble occurs, it indicates that there is leakage.

3

Check with instrument, the common instrument is halogen leak detector. When using the halogen leak

detector for check, the key is the propane flame color depending on which the judgement is made. When

there is no leakage, the flame color remains unchanged, when there is a little leakage, the flame is

greenish, when there is large leakage, the flame is bluish or purple.

Cool

Cold

Hot

Warm

Expension 

Valve

Compressor

Evaporator 

 Condenser

Gas

Gas

Liquid

Liquid

Low Pressure

High Pressure

Figure 16 A/C System Process

→

→

→

→

314

Have a focus inspection on the following area:

a. Each pipe union joint and valve connection.

b. All hose, especially near the pipe union.

c. Compressor shaft seal, front and rear cover, gasket, oil fill plug.

d. Area on the surface of the condenser and evaporator that is scratched, bruised or damaged.

e. Expansion valve inlet and outlet connection and temperature sensor element and the welding position.

3. Check the Refrigerant

Observing from the sight glass, you may understand the refrigerant status and analyze the possible faults:

4. Check Other Parts

Other parts needed to be checked and their check points:

Conditions observed

Possible problems

Clear, no air bubble, A/C emits cool wind

 Refrigeration system is normal

Clear, no air bubble, A/C emits warm wind

 Refrigerant leaked, there is leakage in the system

Occational air bubble. Expansion valve is frosted  There is water mixed in the refrigeration system

Occational air bubble.

 Insufficient refrigerant or air mixed in the system

Clear, there is oil stripe on the glass

Outlet is not cold, no refrigerant

Foamy and turbid

Excessive freezing oil

Checked Part

Check Points

There shall be no dirt and rust on the radiator that hinder the heat
exchange;
The radiator surface has no damage, fissure and hidden trouble that may
cause refrigerant leakage.

Electromagnetic Clutch

Clutch operation is normal. When switched on, the compressor shall
operate, clutch can not slip.

Compressor Belt

Belt tension of 250N is normal, belt is not broken and damaged.

Wire

The electromagnetic clutch and blower power cable shall be not damaged
and overheated; the connection shall be reliable, and the protective
grommet through the metal plate shall be kept good and without damage.

Hose

Refrigerant hose and condenser pipe shall be secured and shall not be
damaged by approaching the other overheated parts, moving parts and
sharp parts.

Evaporator Condenser

315

II. A/C System Diagnosis and Troubleshooting

Table 1

Abnormal high pressure of the high pressure pipeline

Abnormal low pressure of the high pressure pipeline

Abnormal high pressure of the low pressure pipeline

Abnormal low pressure of the low pressure pipeline

High and low pressure can not be established

Sight glass has air bubble

 Compressor inlet side is frosted

 Compressor noise

 Abnormal heating on the compressor

Evaporator is frosted

Drier filter ices up

A/C does not refrigerate or the cold air is insufficient

×

×

×

×

 Excessive refill of refrigerant

Drain p roper amount of

refrigerant

×

×

×

×

 Too little refill of refrigerant

Rep air the gas leak area, refill

p roper amount of refrigerant

×

×

×

×

 Refrigerant is leaked all

Rep air the gas leak area, refill

p roper amount of refrigerant

×

×

×

×

×

×

There is non-clotted gas in

the sy stem

Loosen receiver and

condenser inlet connector,

discharge the non-clotted gas

×

×

Excessive freezing oil in the

sy stem

Check comp ressor freezing

oil level, adjust it

×

 Excessive high temp erature

of condenser inlet

Perform the check at the

p lace with good ventilation

 There is dust in the

condenser core, air channel

within the condenser is

blocked or suffocated

Use compressed air or water

to flush and remove the dirt

on the condenser

 Condenser fan faulty or

broken

Check the wiring status and

the fan motor, correct or

rep lace it

×

×

 Excessively low temp erature

of condenser inlet

Stop  the operation of the

refrigeration sy stem

×

×

×

Drier blocked

Clean

Air channel in the evap orator

blocked or suffocated

Remove the dirt on the

evap orator

Evap orator fan fault, p oor

blower motor wire connection

Check the wiring status and

the fan motor, correct or

rep lace it

×

×

×

There is dirt in evap orator

core

Use the compressed air to

clean the evaporator core

×

×

×

×

×

×

×

Problem Sy mp tom

Possible Cause

Troubleshooting

×

316

A

bnor

m

al high pr

es

su

re

 of

 the
 high pr

es

su

re

 pipe

line

A

bnor

m

al low

 pr

es

su

re

 of

 the
 high pr

es

su

re

 pipe

line

A

bnor

m

al high pr

es

su

re

 of

 the
 low

 pr

es

su

re

 pipe

line

A

bnor

m

al low

 pr

es

su

re

 of

 the
 low

 pr

es

su

re

 pipe

line

H

igh a
nd low

 pr

es

su

re

 c

an

 not be

 e

sta

blis
he

d

Sight gla

ss

 ha
s a

ir bubble

 Com

pre

ssor inle

t side

 is froste

d

 C

om

pr

es

sor

 nois

e

 A

bnor

m

al he
ating on the

 c

om

pr

es

sor

Eva
por
ator

 is

 f

ro

ste

d

Drie

r filte

r ic
es

 up

A/C d

oe

s n
ot refrig

erate o

r th

e co
ld

 air is in

su

fficien

t

Dirt in the evaporator core, or

poor fit between the

expansion valve sensing unit

and evaporator outlet

Check and correct it

Non-evaporated refrigerant

steam enters into compressor

Service the evaporator and its

components such as fan

expansion valve opening is

excessively big or faulty,

refrigerant supply is

excessive

Adjust the expansion valve,

check the sensing unit and the

evaporator outlet for fitness,

replace it as necessary

×

×

Expansion valve opening is

too small

Adjust expansion valve

×

×

×

×

Expansion valve fault, spinal

corrosion or leakage

Replace expansion valve

×

×

×

The refrigerant pipeline

between the expansion valve

sensing unit and the

expansion valve is damaged or

broken

Check and replace the

expansion valve and pipeline

×

×

Expansion valve blocked by

ice or dirt

Recycle the refrigerant,

remove and clean the

expansion valve, use the

vacuum pump to drain the

water in the system and then

refill the refrigerant

×

 Refrigerant pipeline blocked

Disassemble and check the

part

×

 Compressor solenoid clutch,

bearing and pulley wear

Check and replace concerned

worn parts

×

×

×

×

×

×

 Compressor reed is damaged,

exhaust valve leaks

Check and replace the

compressor

×

 Compressor inlet blocked

Check and clean

×

×

Drive belt loose or broken

Replace or replace it

×

Excessively low temperature

in the vehicle compartments

Adjust the selection switch

×

×

×

×

System pipeline leaks

Check the leak area, refill

proper amount of refrigerant

×

×

×

Problem Symptom

Possible Cause

Troubleshooting

×

×