Midea HS-36I User manual

ICE-MAKER
Service Manual
Features
●Auto ice-making technology
●Built-in design
●Low noise operation
●Thick insulation for energy efficiency
●Latest No. 2 micro-biological technology
0

CONTENT
CONTENT
1. Content…………………………………………………….
1
2. Specifications
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.
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..
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. 3
3. Function Schedule
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......
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.
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. 7
4. System Flow Chart
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..
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...
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8
5. Circuit Diagram
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..
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.
…
.
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.
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9
6. Maintenance Service and Trouble Shooting
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.
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... 10
7. Exploded View
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...
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30
8. List of Parts
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..
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.
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31
1

Specifications
Specifications
Models
Net capacity
(L)
HS-36I
28
Color
Black
Power Supply
(V/Hz)
220~/50
Rated Input Power
(W)
/
Power Consumption
(kW.·h/24h)
/
Net Weight
(kg)
30
Gross Weight
(kg)
Unit Dimension
(D*W*H)
(mm)
Packing Dimension
(D*W*H)
(mm)
Container Quantity
40'HQ
(PCS)
33
450*380*629
496*430*650
512
3

Safety precautions
Function Schedule
Function Schedule
●Auto ice-making technology
●Built-in design
●Low noise operation
●
Thick insulation for energy efficiency
●
Latest No. 2 micro-biological technology
7

System Flow Chart
System Flow Chart
1 Schematic diagram of System Flow Chart
2 Brief Description of System Flow Chart
Model UL-ZB28C2 is a direct cooling single-system appliance.
When the appliance is just powered on, the refrigerant flows in the
sequence: 1->2->3->4->5>1
8

C
S M
CL
t
M
Circuit Diagram
Circuit Diagram
1Schematic Circuit Diagram
Brief Description of Control Principle
Model UL-ZB28C2 is a direct cooling single-system Ice-marker . A
mechanical type of all the control is generally adopted. The thermostat
directly controls the start and stop of compressor, and hence the
appliance temperature.
9

Maintenance Service and Trouble Shooting
Maintenance Service and Trouble Shooting
1. No cooling
No cooling
If compressor
can run after it stop to
run five minutes and
give power.
NO
Check and repair according to
the section of "the compessor
doesn't work".
YES
If compressor
can run naturally and
temperature raising
of condenser is
very low
YES
NO
Refrigerant
leak,check and
repair charge
refrigerant again.
Block by ice or dirty
things,change filter and change
refrigerant again.
!
When charging refrigerant,we must
notice to make refrigerant true.
10

Maintenance Service and Trouble Shooting
2 The compressor doesn't stop
Compressor doesn't
stop
Does the appliance
refrgerate?
NO
Check and repair according to
the section of "No cooling".
YES
Is cooling capacity
insufficient.
NO
Check and repair according to
the section of "Cooling capacity
is insuffcient".
YES
1 The thermostat was
set at the coldest position.
2 The ambient temperature is very high or
the appliance is near by heat resource.
3 The door was opened too many
times or there are more
fresh food inside.
NO
Adjust and instruct
consumer how to use.
NO
Check and repair the main
control panel
11

Maintenance Service and Trouble Shooting
3 Cooling capacity is insufficient
Cooling capacity is
insufficient
Is the ambient
YES
temperature low than
16°C
Check the therostat is
correct?
YES
NO
Does the refrigerant
leak siowly?.
Adjust and instruct
consumer how to use.
Repair
12

Maintenance Service and Trouble Shooting
4 Troubleshooting Guide
PROBLEM
POSSIBLE
CAUSE
APPLIANCE
DOES
NOT
OPERATE.
NOT PLUGGED IN.
THE CIRCUIT BREAKER TRIPPED OR A
BLOWN FUSE.
THE APPLIANCE POWER SWITCH IS SET AT
"0FF".
NOT
PRODUCING
ICE,
UNIT
NOT
COLD
ENOUGH
NCE
ARM
IS
SET
TO
THE
OFF
POSITION.
WATER SUPPLY IS TURNED OFF.
WATER LINE IS CRIMPED.
TEMPERATURE CONTROL IS NOT SET
PROPERLY (POSITION 5 OR 6).
COMPRESSOR TURNS ON AND OFF
FREQUENTLY. THE ROOM TEMPERATURE IS HOTTER THAN NORMAL.
THE DOOR IS OPENED TOO OFTEN.
THE DOOR IS NOT CLOSED COMPLETELY.
THE DOOR GASKET DOES NOT SEAL
PROPERLY.
THE APPLIANCE DOES NOT HAVE THE
CORRECT CLEARANCES.
VIBRATIONS.
CHECK
TO
ASSURE
THAT
THE
APPLIANCE
IS
LEVEL.
THE
APPLIANCE
SEEMS
TO
MAKE
TOO
MUCH
NOISE. THE RATTLING NOISE MAY COME FROM THE
FLOW OF THE REFRIGERANT, WHICH IS
NORMAL.
AS EACH CYCLE ENDS, YOU MAY HEAR
GURGLING SOUNDS CAUSED BY THE FLOW
OF REFRIGERANT IN YOUR APPLIANCE.
CONTRACTION AND EXPANSION OF THE
INSIDE WALLS MAY CAUSE POPPING AND
CRACKLING NOISES.
THE
APPLIANCE
IS
NOT
LEVEL.
THE
DOOR
WILL
NOT
CLOSE
PROPERLY.
THE APPLIANCE IS NOT LEVEL.
THE DOOR IS REVERSED AND NOT
PROPERLY INSTALLED.
THE GASKET IS DIRTY.
THE
BUCKET
IS
OUT
OF
POSITION.
ICE CUBES ARE MELTED TOGETHER APPLIANCE DOOR IS OPENED TOO OFTEN.
TEMPERATURE CONTROL IS NOT SET
PROPERLY.

Maintenance Service and Trouble Shooting
5 Normal Phenomena—Not Troubles for Appliances
In a domestic appliance, there is not only a complicated electric control
system, but also a refrigerating system that is difficult to discern whether it
is in a good working condition. Both the systems are related and affect
each other. If a certain part of a appliance works abnormally .Its
refrigerating efficiency will decrease ,operation properties will become
unstable ,or even it cannot be used normally for those serious cases.
Appliances are generally of larger volume ,once troubles appear ,to
send them to a service department is really a tough thing ,if such is the
case ,the user will always be in suspense ,sometimes ,normal phenomena
will be erroneously regarded as troubles .Therefore ,before we deal with
the topics of frequently occurring troubles of appliances and their
remedies ,we should firstly give a brief account of some normal
phenomena which are not troubles .In case any one of such phenomena
occurs ,there is no need to worry about it ,and the user can use it at total
ease .
1).When the compressor of a appliance has just stopped running ,a
rumbling sound can be heard from inside its evaporator .This is a sound
caused by the flowing of refrigerant in the evaporator tubing .Because the
pressure difference is still greater after the compressor has just stopped
running ,the refrigerant will flow for a certain time , therefore ,this sound is a
normal phenomenon.
2).A click sound can often be heard from the appliance .This is a
normal sound produced by the pull-in or release of the armature of a
current deadweight start relay when starting the compressor .The
compressor motor will produce a slight and uniform sound while it is
running .This sound is not easy to be heard in the daytime ,but of course it
can be heard distinctly at night.
3).The compressor consists of an electric motor and a compressing
apparatus .During its normal operation ,the motor's stator core and
windings will rise to a temperature in the range of 100°C~110°C ,and the
temperature of the piston and cylinder of the compressing mechanism can
also reach as above 100°C due to the heat produced when compressing
refrigerant .Most of the heat radiates to the air through the compressor
casing ,therefore ,its casing is generally at a temperature between 85°C ~90°C
,it is very hot ,particularly in summer when the ambient temperature is
higher .All these are normal phenomena .
4).For the direct cooling appliance ,a kind of irregular crack sound can
be often heard when the compressor is running for a certain period of time
or has just stopped its running .This sound is caused by the stress relief
due to expansion and contraction when temperature changes ,and will not
affect the normal application of appliance .
14

Maintenance Service and Trouble Shooting
6 Common Troubles in Appliances and Their Remedies
Causes for troubles occurring in appliances are closely related to the
quality of components and workmanship in assembling by manufacturers
as whether appliances are properly used and maintained .The parameters
generally used to express the working conditions of a appliance include
the temperature inside the appliance ,operation rate ,electric power
consumption ,noise level ,and other functional indexes .If any one of these
parameters is beyond its permissible range ,this indicates that there is a
fault or trouble in the appliance .
During the whole service life of a appliance , the probability of troubles
occurring within a union time is called its failure rate .Making a comparison
between the control circuit system of a appliance and its refrigerating
system ,we can find that the failure rate of the former is higher ,and that of
the thermostat is the highest . In troubleshooting , the first thing you must do
is to determine where the trouble comes from --- the control system or the
refrigerating system .There is general no trouble indicating instrument
mounted on the dome stick appliance ,locations and natures of troubles
should be determined according to their respective
features ,therefore ,experience in servicing is very important to
troubleshooting. Service technicians with rich experience can correctly
locate them and take reasonable remedy measures based on their
comprehensive analysis of trouble characteristics as well as operating
conditions for various kinds of appliances .
Three Essentials for Checkup
1) Look
a) Check the tubing of refrigerating system for cracks and various
welding points for leaks ;if leakage occurs ,an oil stain can be seen
definitely .
b) Check the suction and exhaust pressure values (high pressure and
low pressure) of compressor to see whether they are normal .
c) Check the conditions of frost attached to its evaporator and gas
return tube .It is abnormal if frost has formed on part of the evaporator or
there is no frost attached to it .
d) Pay attention to the speed of temperature drop inside freezer
compartment .It is abnormal if the speed of temperature drop is obviously
slower than the corresponding normal speed .
e) Check the environment to see whether it is suitable for placing a
appliance .
f)
layer .
Check appliance door seal ,case ,table surface and heat insulation
g) Look at the main control board to ascertain if various indication
states are normal.
2) Listen
a) Listen to the noises produced when the compressor is running
15

Maintenance Service and Trouble Shooting
Hums from a fully enclosed aggregate unit is the sound caused by
overload indicating that the motor cannot be started normally ,meanwhile ,a
clattering sound can be heard from inside the start relay ,which is produced
because the start contacts cannot be released normally .A whistling sound
is caused by the high pressure gas flowing out of the crack of the pressure
tube inside the compressor ,and clucks are the sound of striking after the
suspended spring inside the compressor has broken .
During the normal operation of compressor, a slight and uniform hum
sound due to undulation of electric current can be heard generally ,this is a
normal phenomenon .However ,if it sounds like "tong ,tong …",i.e., an
impact sound inside the compressor ,this means that a large quantity of wet
vapour of refrigerant or refrigerating oil has come into the compressor
cylinder ;if it sounds like "dang ,dang…", a striking sound of metal parts
inside the compressor ,this means that some moving parts have loosened
(note to differentiate this sound from those formed during starting or
stopping the compressor).
b) Listen to the sound caused by the flowing of gas in the evaporator
Open the appliance door while the compressor is in operation, incline
your ear and listen attentively the gas flow sound inside the evaporator .If it
sounds like gentle whistling accompanied by a sound similar to water
flowing ,this is the sound produced by the normal circulation of refrigerant
within the evaporator .In case only the gas flowing sound can be heard and
there is no water flowing sound ,this indicates that the refrigerant has
already percolated .If neither the flowing sound nor the gas sounds from
the evaporator can be heard ,this means that the filter or capillary has been
clogged .
3)Touch and Feel
a) Feel the compressor when running ,its temperature should be
generally less than 90°C in the normal state (it may exceed 90°C in case
of running for a longer period of time ).
b) After the compressor has operated normally for 5~10 minutes ,
ouch and feel the condenser ,the temperature of its upper part should be
higher than that of its lower part (or its right part is hotter than its left
part ,depending on the type of condenser coil ),this indicates that the
refrigerant is circulating . If the condenser is not hot ,this means the
leakage of refrigerant .In case the condenser radiates heat for only several
minutes and then cools down ,this means that the filter and capillary have
been clogged .As for the forced air cooling condenser ,hot air will be blown
out of it ; this means that the system is out of order .
c) Feel the filter's temperature .During the normal operation of
refrigerating system ,the temperature on the filter's surface should be a
little higher than the ambient temperature ;if you touch it with your
hand ,you will have a sense of slight heat .In case dew condensation
appears due to the fact that its temperature is obviously lower than the
16

Maintenance Service and Trouble Shooting
ambient temperature ,this means that most meshes of its screen has been
clogged ,resulting in an obstructed flowing of refrigerant ,thus causing a
drop in temperature due to throttling .
d) Feel the temperature of exhaust gas from the refrigerating
system .the exhaust gas should be very hot and this is the normal working
state .For those appliance with enclosed type of compressor refrigerating
system, no frost or dew drop will from on the gas suction
tube ,otherwise ,there is something wrong in the system (Frosting and dew
condensation may appear for a very short time period when just starting the
machine ,this is a normal phenomenon ).
Because a appliance is a combination of several components ,they are
related and have influence on each other In case an abnormal
phenomenon has been found through the above-mentioned checkups ,you
need not to make a hasty conclusion based on only one abnormal
phenomenon .It is advisable to find out two or more abnormal
phenomenon ,or conduct troubleshooting comprehensively with the aid of
instruments or other ways ,because several kinds of troubles may share a
common abnormal phenomenon ,and two or more abnormal phenomena
may occur simultaneously due to a certain trouble .With this method ,you
can reject some suspicious troubles and finally make a correct judgment .
7 Analysis of Troubles and Troubleshooting
A. Poor Refrigerating Effect
The so-called "poor refrigerating effect " refers to the fact that the
appliance can operate and appliance normally ,but the temperature in
the appliance cannot drop to the prescribed value under the stipulated
working conditions .In view of there are many causes for this
phenomenon ,we are going to discuss and analyze it in the following 7
aspects :
1) Leakage of refrigerant
Analysis of Trouble
The leakage of refrigerant in the system will result in an insufficient
refrigerating capacity ,the resulting phenomena are its lower gas suction
pressure and exhaust pressure as well as higher exhaust gas
temperature. The exhaust tube feels rather hot ,and a continuous gas
flowing sound louder than usual can be heard at the outlet of the
capillary ,and no frost or a smaller quantity of loose frost appears on the
evaporator .After shut down ,the balance pressure in the system is usually
lower than the saturation pressure corresponding to the same ambient
temperature .
Remedy
In case there is leakage of refrigerant from the system ,do not hurry to
recharge it with refrigerant ,manage to find out leak points immediately ,and
make a note of from where it leaks ---welding points and parts .After having
them repaired ,recharge refrigerant .
17

Maintenance Service and Trouble Shooting
many joints and sealed surfaces in a
There
are
so
appliance ,accordingly ,quite a lot potential leak points do exist in the
system .In troubleshooting ,pay attention to those parts that are liable to
leak ,check main connection points for oil seepage and tubing for cracks .If
there is no severer leak point ,charge the system with nitrogen and detect
leak points with the commonly adopted method ,repair
them ,evacuate ,charge the system with refrigerant ,and then turn on the
appliance to make a test run .
2) Too much refrigerant charged into the system
Analysis of Trouble
a) In case the amount of refrigerant charged into the system exceeds
its nominal capacity ,the superfluous refrigerant will of course take some
space of the evaporator ,thus reducing its heat-dissipation area and hence
the refrigerating efficiency of the system .The abnormal phenomena
caused by this reason are as follows :the gas suction and exhaust
pressures are generally higher than their respective normal values ,the
temperature of its condenser is higher and the electric current of the
compressor rises ,loose frost forms on the evaporator ,the appliance
temperature drops slowly ,and frost appears on the gas return tube .
b) In case excessive refrigerant has been charged, the liquid
refrigerant that cannot evaporates in the evaporator will return to the
compressor ,and thus a phenomenon of "liquid striking" will occur .The
liquid refrigerant evaporates and effervesces as soon as it flows into the
refrigerating oil at the bottom of compressor .If the condition is
severe ,foams will fill all over inside the compressor housing and be sucked
by the piston ,causing damage to the components of compressor .
Remedy
According to the operating procedures, it is mandatory to turn the
machine off ,and several minutes later ,open the refrigerant charging tube
and et the refrigerant escape from it ,replace the dry filter ,recharge
refrigerant after evacuating ,and then seal the charging port .
3) There is air left in the refrigerating system
Analysis of Trouble
Residual air in the refrigerating system will reduce its refrigerating
efficiency .The prominent phenomena are the increase in its gas suction
and exhaust pressures (however ,the gas exhaust pressure will not exceed
its rated value ),obvious increase in temperature in the segment from the
compressor outlet to the condenser inlet .Because there is air in the
system ,both the gas exhaust pressure and temperature will rise ,and
moreover ,the gas flowing sound is intermittent and obviously louder .
Remedy
After shut down for several minutes ,open the tubing ,evacuate it and
then recharge the system with refrigerant .
4) Low efficiency of compressor
18

Maintenance Service and Trouble Shooting
Analysis of Trouble
Low efficiency of a refrigerating compressor refers to the actual
reduction of gas discharge capacity ,and hence the corresponding
reduction of refrigerating capacity ,under the condition that the refrigerant in
the system is unchanged .This phenomenon occurs mostly when the
compressor has been used for quite a long time ,its moving parts have
worn to a considerable degree ,fit clearance between various parts have
increased and sealing property of its gas valve has deteriorated ,resulting
in an decrease in its actual gas discharge capacity .
Methods of Judgment
Measure the high and low pressures with pressure gauges to see
whether they are normal .If an abnormal sound comes from the compressor
or the temperature of its causing is too high ,Cut the discharge port open
and operate the compressor ,feel it if there is pressure at the discharge port
with your finger (For a normal compressor ,its discharge port is difficult to
be blocked with your finger if you just apply a little effort).
5) Too thick frost layer formed on evaporator
Analysis of Trouble
If a direct cooling appliance is to be used for a prolonged period of
time ,be sure to defrost its evaporator regularly ;if you fail to do so ,the frost
layer on the evaporator tubing will become thicker and thicker .Heat
conduction will be severely affected when the whole tubing is wrapped with
a transparent ice layer ,and finally the temperature in the appliance
cannot drop down to the prescribed range .
Remedy
Turn the appliance off , and make preparations for defrosting ,open the
appliance door to let the air come in ,or use a fan to speed up air flowing
so as to shorten the time needed for defrosting .Never strike the frost layer
with any iron tools or wood stick in order to avoid damage to the evaporator
tubing .
6) Refrigerating oil left in evaporator tubing
Analysis of Trouble
During the process of refrigerating cycles , a little refrigerating oil may
remain in the evaporator tubing ,and after a longer time of operation ,if
there is considerable refrigerating oil left in the evaporator ,the heat
conduction effect will be severely affected ,thus causing a poor refrigerating
effect .
Remedy
It is quite difficult to determine whether this trouble is caused by the
refrigerating oil left in the evaporator tubing ,because this kind of
phenomenon and other several trouble are tends to be confused .Generally
speaking ,you can make a judgment based on the frost formed on the
evaporator .If the frost does not cover the evaporator , and moreover ,it is
loosely formed ,you can make a judgment that the deterioration of
19

Maintenance Service and Trouble Shooting
refrigerating effect is due to the accumulation of refrigerating oil left in the
evaporator tubing in case no other troubles have been found . To clear off
refrigerating oil left in the evaporator ,dismantle the evaporator ,purge it
thoroughly and then dry it .In case it is difficult to dismantle it ,charge
refrigerant from the evaporator inlet to wash it several times ,then purge
and dry it with nitrogen .
7) Flowing obstructed in refrigerating system
Analysis of Trouble
Because the refrigerating system was originally not purged
thoroughly ,some of the filter screen meshes have been clogged by dirt
accumulated in the filter after using it for a certain time of period ,thus
resulting in a decrease in flow rate ,and hence a poorer refrigerating effect .
The abnormal phenomena caused by this kind of slight clogging in the
system are as follows: the gas discharge pressure is lower ,the
temperature of discharged gas drops down ,the position clogged has a
temperature lower than that in normal conditions ,and for a severe
clogging ,even dew condensation as frosting may appear .
Remedy
Purge the tubing , and after replacing the dry filter with a new one or
clearing it thoroughly ,recharge the system with refrigerant and seal the
charging port .
B. No Refrigerating
The phenomenon that the compressor runs normally , but no frost (or
only a little frost ) appears on the evaporator ,and the appliance
temperature does not drop down is called "no refrigerating". There are
many causes for this trouble and it is relatively complicated , too . In
servicing ,special attention to finding direct causes for this
phenomenon .Three main potential causes for this trouble are analyzed
below :
1) All refrigerant in the system has leaked out
Analysis of Trouble
Leak points in the refrigerating system have not been found and
repaired timely ,thus resulting in the total escape of refrigerant .There are
two kinds of leakage :I) slow leakage for instance ,when we want to use a
appliance that has been put out of quite a long time ,we find the leakage
of refrigerant ,or in the course of its operation ,we have found that the
appliance is gradually becoming not so cold and finally no refrigerating
cab be achieved ; ii) fast leakage in that case ,all the refrigerant will
escape swiftly due to abrupt rupture of system tubing .
Symptoms of total leakage of refrigerant are mainly asfollows : the
compressor can be started easily (if there is no damage to the compressor
parts) and its operating current becomes low ,its gas suction pressure is
high and discharge pressure is lower ,the gas discharge tube feels rather
cold ,no sound of gas eruption from the liquid in the evaporator can be
20

Maintenance Service and Trouble Shooting
heard ,and no will gush out of the process tube if you cut it open after
shutdown .
Remedy
Check the whole machine , particularly those locations which are liable
to leak .After leak points have been found ,repair them or replace them with
new parts according to specific circumstances ,then evacuate the system
and finally charge refrigerant.
2) Refrigerating system has been clogged
a) Clogged with Ice
Analysis of Trouble
The dryness treatment for the major parts in the refrigerating system
has been performed improperly, the effect of air purging for the whole
system is not good ,or the water content in the refrigerant is out of
standard ,all these will cause the expansion valve to be clogged with
ice .The symptom for this trouble are as follows :the appliance sometimes
can refrigerate and sometimes cannot :the appliance compartment works
normally at the beginning ,but after working for a certain period of
time ,frosting begins at the clogged position ,evaporation temperature
reaches below 0°C , water will accumulate at the narrow part of the capillary
and clog it gradually ,then frost begins to melt at the evaporator ,no gas
flowing sound can be heard ,and the gas suction pressure assumes a state
of vacuum .Note that these phenomena will appear intermittently ;
sometimes ,the appliance works well ,and sometimes not well .In order to
determine whether it is clogged with ice ,heat the suspicious points with hot
water to make ice melt ,and after a while if a gas flowing sound resulting
from an abrupt gush is heard and the gas suction pressure rises as well ,it
can be confirmed that the trouble is caused by ice clogging .
Remedy
If there is too much moisture in the refrigerating system, it is advisable
to release the refrigerant, purge the tubing with nitrogen, and then charge
the system with the filtered refrigerant. However, the commonly adopted
method is to connect a filter with moisture absorbers (such as silica-gel,
anhydrous calcium chloride) to the refrigerating system so as to filter out
the moisture from the system, then replace the filter, evacuate it again and
finally charge the system with refrigerant.
b) Clogged with dirt in capillary
Analysis of Trouble
The capillary inlet is a place where coarse-grained dirt or refrigerant oil
in the system will tend to settle down and clog it. In case considerable dirt
accumulates there, the whole filter screen may be blocked totally, making
the refrigerant unable to go through. Clogging with dirt exhibits the same
symptoms as that with ice, namely, higher gas suction pressure, lower
temperature of discharged gas, and no gas flowing sound from the
evaporator. The difference between the both is as follows: if the clogging is
21

Maintenance Service and Trouble Shooting
caused by dirt , tapping the suspicious clogged point (generally in the
capillary or the connection joint of the filter) may cause the refrigerant to
flow through partially, resulting in some corresponding change, whereas in
that case if you heat it with a hot towel, no reaction will happen, no flowing
sound can be heard, moreover, there is no periodic change. After rejecting
the possibility of ice clogging, it can be generally considered as the
clogging due to dirt .
Remedy
Dismantle the system, remove the dry filter from it, purge the tubing with
nitrogen, install a new filter, then evacuate it and finally charge it with
refrigerant.
C) Clogging in filter
Analysis of Trouble
Total clogging of a filter is rarely to occur. This trouble is mostly caused
by the paste-like matter formed from the substances filled into the system
or other dust after the appliance has been used for a longer time, or by
the dirt accumulated gradually inside the filter. Sometimes, tapping the filter
nay cause a passage for flowing, Touching it with your hand, you will feel
that it is cooler compared with its temperature in the normal state.
Remedy
The same as described in the capillary clogging with dirt.
3) Troubles of Compressor
a) Breakage of gas suction and discharge valve blocks
Analysis of Trouble
The compressor works by means of the opening and closing of gas
suction valve and discharge valve to suck and discharge the refrigerant. If
the valve block is broken, the refrigerant can not be discharged, and hence
no refrigerating can be achieved.
Method for making judgement
It is quite difficult to differentiate this trouble from others because they
often have similar symptoms. In repairing, firstly, hear attentively if there is
some abnormal sound coming from the compressor (sometimes , the
broken pieces of valve block may strike against the cylinder), and feel the
compressor casing with your hand to ascertain whether it is too hot, this is
also helpful to the troubleshooting; secondly, measure the pressures at the
high and low pressure ports of the compressor with pressure gauges, if the
gas suction valve block is broken, the suction pressure gauge pointer will
swing violently and the suction pressure is very high, whereas when the
gas discharge valve block is broken , the discharge pressure gauge pointer
will swing drastically and the discharge pressure is very high. In the both
cases, stop the compressor at once, and if technique is available, open the
cylinder cover and check up the valve block, repair it, or replace it with a
new one,
C. Sudden stop of Compressor during Its Running
22

Maintenance Service and Trouble Shooting
The cause of sudden stop of a compressor during its running is mostly
that the gas suction pressure and/or discharge pressure exceed their
respective prescribed ranges, thus making a pressure-operated protective
relay shut off the power to the compressor and stop it. In the following we
discuss mainly the reasons for causing excessively high gas discharge
pressure and low suction pressure.
1) Stoppage due to excessively high gas discharge pressure
A) Too much refrigerant charged into the system
Analysis of Trouble
The phenomenon, such as loose frosting and poor refrigerating effect,
may occur if excessive refrigerant has been charged into the system.
Superfluous refrigerant will occupy a certain space of the evaporator, thus
reduce its heat dissipating area, and the phenomenon of "liquid striking"
may occur, too. Meanwhile, dew or frost condensation may occur on the
gas return tube, and the gas discharge pressure will obviously rise, when it
reaches the threshold value, the protective relay will actuate and shut off
the power supply to the compressor.
Remedy
Open the tubing, re-evacuate and then charge the system with a proper
quantity of refrigerant.
b) Air left in the system
Analysis of Trouble
The residual air in the system will circulate together with the refrigerant
in the system. The major symptoms caused by this residual air is higher
gas discharge pressure, higher discharged gas temperature (the gas
discharge tubing is considerably hot when you feel it with your hand), and
poorer refrigerating effect. Furthermore, the gas discharge pressure will
exceed its normal value when the compressor has run for a period not too
long, thus making the protective relay actuate and bring to a stoppage.
Remedy
Check up how the air has been left in the refrigerating system.
Generally, there are two possibilities: one is that the air has been sucked
into the system when repairing due to carelessness, or it has not been
purged out totally when evacuating the system; the other is that there are
leak points at the low pressure end of the refrigerating system. Leak points
appear mostly in those low temperature parts or assemblies, because the
evaporation temperature is lower for such low temperature devices,
especially at the low pressure end, it is easier for the air goes into the
system. Once it has been ascertained that air does exist in the system, you
have to open the tubing, re-evacuate it and then charge it with refrigerant.
2) Stoppage due to electric troubles
a) Thermostat is out of control
Analysis of Trouble
In case the thermostat does not work in its good order or its
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