Refrigeration and Air Conditioning Principles

8/13/2019 Refrigeration and Air Conditioning Principles

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Refrigeration and AirRefrigeration and Air

Conditioning PrinciplesConditioning Principles

Presented By : Mark Crook


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A i r Con d i t i o n i n g p r i n c i p l es a n d p r a c t i c e

I n t r o d u c t i o n

Air conditioning in this country is normally associated with providing a cool situation during any hot spells. In its true sense, asthe name implies, air conditioning deals with total air quality and not

just cooling. A complete system will therefore consist of:

H eating elements

In far too many cases, instead of having integrated system, 'centralheating' are installed separately for use during cold conditions.

F resh air supply

This means relatively odour and dust free air containing replacementoxygen for that use by normal respiration. A poorly designed systemrelies on opening door and windows, whereas there should be aducted supply which can have a continuous and controlled expulsionand intake provision.


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H umidity Control

This important aspect will be discussed at lengthlater.

It is virtually impossible to meet exactly theindividual and personal requirements of everyoneworking in and/or visiting a particular area.Although very important, far too much emphasis is

placed on simply maintaining an acceptabletemperature.


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Basic Science

Nature of matter

One definition of an atom that is sufficient for the needs ofunderstanding refrigeration is:-

"The smallest particle of a substance that has all of thecharacteristics and properties of that substance. "

Thus one atom of hydrogen has the distinctive and unique propertiesof that gas and it is different from say an atom of oxygen.


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All matter consists of an arrangement of atoms. Some arrangements(called molecules) are combinations of different atoms and this cancreate a whole range of substances that have properties that are totally

different from those of the individual atoms that form thearrangement. For example two atoms of the gas hydrogen whencombined with form a stable molecule of a liquid-WATER.

One very important range of chemicals is based -upon combinationsof carbon, hydrogen, fluoride and chlorine that form the structure ofmany different types of refrigerants. They are often referred to asHALOCARBONS - because of the ring like structure (halo) ofvarious atoms of the chemicals mentioned above, that can be grouped

around a carbon atom. Nowadays they tend to be classified as CFC's -which stands for Carbon Fluoride Chlorine, which is rather moredescriptive.


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Water can be varied from its normal liquid state into a solidor a vapour. The vapour will then behave in a similarfashion to a gas - but it will have a very different behaviour

pattern from the two gases that have combined to form thewater vapour. These variations can be brought about bychanging the pressure and/or the temperatures of theice/water/steam. By lowering the temperature it is possibleto obtain the solid form of ice and conversely the gaseousform, known as steam, is produced by raising thetemperature. These changes are easily reversible and areknown as physical changes.


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Temperature

Temperature has an important effect on determining the particular properties of a substance, so it is necessary tounderstand more about its nature.

For all practical purpose the particles that formsubstances are never stationary.

Even if a solid object is stationary the particles that formthe material are constantly in motion. WITHIN THECONFINES OF THE SHAPE OF THE OBJECT , or in thecase of fluids (liquids and gases) WITHIN THECONFINES OF THEIR CONTAINING VESSEL .


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Fahrenheit Scale

Although the Fahrenheit system is used less frequently in modern

technology, it is based upon the same idea of using points to set up atemperature scale. Interestingly the scientists of the day appreciatedthat there were temperature below the freezing point of water and sothe lowest temperature though to be

Be possible was set at O oF and the 'fixed' freezing point set 32'F

above this. This was imaginative but rather a long way out. Laterresearch showed that the real 'bottom of the scale' is actually minus456'F.

It was also decided subdivide the range between boiling and freezinginto 180 divisions because there are more numbers which divideexactly into 180 than there are into 100. This gives more scope formarking out temperature scales and greater 'whole number' accuracyof specification. Thus the boiling point for water is 212 oF.


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Evaporation and boiling of liquids

The 'energy' of a body or substance, that is its ability to do work, can be in many forms. Except for chemical energy (which can bedisregarded for a study of refrigeration) these forms are frequentlyinterchangeable but the TOTAL energy of a body or substance willremain the same unless some is added or removed by external effects.

The movement of particles within a liquid (i.e. the temperature) willcontribute to the energy of the liquid, this is its HEAT energy. TheTOTAL energy will be a sum of heat energy plus that due to pressure,

position and the velocity of the liquid when it is flowing.


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PRESSURE

M easur ement and Uni ts

Pressure is defined as being - Force applied divided by the AREA overwhich it acts.

i.e. Pounds per square inch - kilograms per square centimetre etc.

The S I unit of force is the Newton (N) (approximately equivalent to

of a pound), and the basic unit of area is the SQUARE METRE.So the basic S I unit of pressure is given as N/M 2.

One N/M 2 is also known as a PASCAL (Pa). The actual value of 1 Pais very small:-

10 000 Pa (also called 1 bar) is approximately 1 atmosphere (about14.7 psi) thus it is more practical gauges in kilopascals (kPa) i.e. unitsof 1000 Pa.


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For pressure below atmospheric, i.e. those in the vacuum range, theunits can be

Inches of mercury ("Hg) 30Hg0Hg

Millimeters of Hg (also called Torrs)

Microns (1 micron = 1000 th of a millimetre)(not very practical - rarely used)


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If mass of gas (i.e. a definite number of molecules) is held in acontainer that can have its volume varied. For example inside acylinder with a moveable piston, then as the volume is decreased, thenumber of molecules striking the smaller wall area will increase theforce, and therefore the gas pressure.

This is expressed by Boyles Law - "At a constant temperature(Isothermal) the pressure exerted by a fixed mass of gas will be

inversely proportional to the volume". In other words if the volume ishalved the pressure will double.

Note:- the value of the constant will vary for different gases

for the relationship to be true the temperature must notchange


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GAUGE MARKING

In order to avoid the necessity of looking up the chart each time,many pressure gauges are already calibrated with a temperaturescale to correspond with the refrigerant pressure.

This is exactly the same information in the charts, it is simply presented in this way to make the readings more convenient.

In this example the scale shows that at 38 oF the pressure shouldread 35 p.s.i. for Refrigerant R12.

Note that a separate scale is provided for Refrigerant R22.

GAUGE PRESSURE AND ABSOLU'I'E PRESSURE

When reading the charts, note that some information is in gauge pressure, and some is in absolute pressure. Always check whichtype of gauge you are using to make sure that you are reading thecorrect chart.


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Temperature and volume

If the velocity of the particles striking the surface of the container isincreased the force on the walls increases - and so therefore will be

pressure, but particle velocities increase with temperature. If howeverthe volume of the container can be increased so that the pressure doesnot vary the relationship is defined by Charles Law.

"If the pressure of a given mass of gas is kept constant then the

volume of the gas will proportional to the temperature of the gas" -which is only a way of saying that to maintain a constant pressure of agas trapped inside a container, whose volume can be changed, if thevolume is increased then the temperature must also be increased.

The relationship can be expressed mathematically as:


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The temperature values used must be in absolute units (K)

Both of these relationships can be combined together to form thegeneral gas equation

Note that both P and T must be used in Absolute units

These laws are useful in explaining situations where the total energyof a mass of gas is kept constant. If work is done on or by the gasthen extra energy is added or taken away - and this changes the

relationships. For example the action of moving the piston of a cycle pump accelerates the trapped air, and the corresponding increase intemperature is easily detected at the outlet point.


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Relationship between pressure and temperature.

There is a constant relationship between the temperature ofa particular refrigerant gas and the pressure that exists indifferent sections of a system. Notice that this relationshipwill vary for different refrigerants. Charts are available, as

shown later, which give the relevant pressures andcorresponding temperatures. These are needed in order tohelp with fault diagnosis tests e.g. estimating the quantityof refrigerant within a system .


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Heat

We refer to something that is at a high temperature as being HOT,having a lost of HEAT etc. These generally used terms are not

precise enough for scientific study and in fact can be quitemisleading!

At some time or other 1 am sure that many of you have had particlesat a temperature of about 1300 oC come into contact with your skin -

and you have not been at all bothered!What am referring to? - the simple spark from a grinding wheel or

similar

Why wasn't it damaging? - Although the temperature was very

high the quantity of heat, which it what actually does the damage,was very small.

Heat energy (to give it its full title) is a combination of temperatureand MASS


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Thus the principle under which a refrigeration process takes place is:-

? Have a liquid (refrigerant) at a high pressure and atemperature above its boiling point.

?Reduce the pressure, thus allowing the liquid to boil by taking in heat from the surrounds .

The basic components of a complete refrigeration system are

designed not only to allow heat to be absorbed but, equally important,to recover the refrigerant vapour and convert it back into a high pressure liquid so that the cycle can be repeated.


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L atent H eat

The word LATENT means 'hidden'. In other words the heat that isabsorbed or given up with no effect on temperature. Thus the heatneeded to change a liquid into a vapour is known as the latent heatof vapor isation, and the heat given out on when the vapour isreformed into the liquid state is the latent heat of condensation.Different substances have different latent heat values and theeffectiveness of a refrigerant is largely based upon this property.Water has a very high value but its rise as a refrigerant is obviouslyvery limited. (It can be used in come air conditioning units, wheresystem temperatures need not be within the 'freezing' range).


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Heat Transfer

This is of fundamental importance to the efficient operation of a

refrigerating system. The overall purpose of refrigeration is totransfer heat from one area (the cold zone) and distribute it intoanother zone where it can be efficiently dispersed.

There are three ways in which heat is transferred

Conduction - the transfer of molecular movement through amaterial.

A material that readily allows this to happen is therefore known as agood thermal conductor. Thermal insulators, which are also anessential materials used in refrigeration systems. limit this transferof molecular movement. It is rather like comparing the effect of asnooker ball striking a cluster of static balls with an identical setupusing sponge balls.


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Convention - this effect is confined to fluids, either

liquids or gases. Variations in temperature of the substancecan cause localised expansion (or contraction). If a sectionof fluid is heated it will expand, become less dense than thesurrounding fluid and so it will rise - only to be replaced bycooler, denser fluid flowing into the space that has beenevacuated. Air that is in contact with a warm surface willrise and be replaced by colder air that is drawn into the areaat a low level. This 'air cooling' action (of the source ofheat) is also critical to the efficient operation of many types

of refrigeration unit. In order to improve this heatdistribution process it is often necessary to assist in theremoval of warm air by the use of fans.


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Radiation

Both conduction and convection need to have an interaction between particles. Radiant heat is in the form of energy waves

that can pass quite readily through some substances (or indeedthrough a vacuum) without significantly changing thetemperature of the medium through which it passes. Most of theheat from a glowing electrical element is of a radiant form andwhen the 'waves' come into contact with a surface the particlesof the surface will set into motion - the temperature rises. Themost effective type on the surface for distributing and absorbingradiant heat will be matt black. Shiny and bright white surfacewill reflect some of the heat in a similar way to the reflection of

light by a mirror. Note that so called domestic 'radiators' shouldtherefore be black, or at least dark coloured, and in fact theyshould more appropriately be called 'convectionators'.


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Conduction of heat is probably the most relevant form of transferwithin the basic refrigeration system, but when designing an air conditioning unit the other forms must be carefully considered.

There are three factors that affect the transfer of heat of conduction

1.The nature of the material through which heat must pass

2.The surface area and thickness of the component orstructure

3.The temperature difference between the two surfaces ofthe material.

The behaviour of different materials under different conditions isestablished by experiments, and tables of coefficients of thermalconductivity can be produced.


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Humidity

The human body has its own refrigeration system, which keeps itcool by using exactly the same evaporative principles as describedabove. The body exudes small and usually imperceptible qualities offluid (perspiration) through the skin. This fluid needs heat to changeit into a vapour - and it takes it from the body. This vapour needs to

be absorbed by the surrounding air, which is why an air current helpsto cool by replacing the moisture-laden air by a fresh, and driersupply.

Humidity is a measure of the quantity of moisture, which is held insuspense by the atmosphere. If the humidity is high (i.e. highmoisture content) then the ability of the air to absorb more moistureis restricted and we can feel uncomfortable. If the humidity is lowthen the body can often support quite high temperatures without

being unduly distressed.


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Thus humidity is an essential factor in determining the comfort of personnel.

Humidity will depend upon both the pressure and temperature of theair. It is measured as a percentage of the maximum amount ofmoisture that can be held under the conditions that exist at any

particular time. Hence its more accurate description is RelativeHumidity.

100% is total saturation and extremely uncomfortable, tropical rainforest conditions. Totally dry air, 0%, would be equally unbearableas the drying process would be so rapid that the essential fluids inthe eyes and nose would dry out faster than they could be replaced.

A good air conditioning system therefore is one where the airtemperature is maintained at a reasonably acceptable level and thehumidity level somewhere between 40% and 60%.


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It a volume of air has its temperature reduced (by passingit over cold coils) then the quality of moisture that can beheld is also reduced, the excess water vapour willcondense out of the air (e.g. the water on a window pane in

cold weather).

If this is then passed into a habitable area it will be able toabsorb moisture again as it warms up, that is its relativehumidity will be lowered.

The basic Refrigeration Cycle


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The basic Refrigeration Cycle

? (All descriptions will be related to the equipment and controlsused with medium or large size refrigerating and air conditioning

plant).

1 The 'high side' will contain high pressure liquid at a point 'list before the expansion valve.

2 The expansion valve controls the rate, at which refrigerant flowsinto the evaporator, which will be at low pressure (the start of the'low side').

3 Due to the drop in pressure the liquid refrigerant will start tovaporise and in so doing will absorb heat from the surrounds. Whenthe expansion valve settings match the demand of the system, ALL

of the liquid should vaporise. The vapour will usually leave theevaporator at a temperature slightly above the boiling pointassociated with the pressure in the evaporator. i.e. It will be slightlySUPERHEATED.


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4 The low-pressure vapour will be drawn from the evaporator by thecompressor through accumulator. The purpose of this is to trap anyliquid, which may not have been vaporised.

5 The compressor (usually driven by an electric motor) will pump thegas to a high pressure. In doing so the temperature of the vapour willrise considerably.

6 The compressor outlet is the start of the 'high side'. It connects to thecondenser where the latent heat of condensation is removed. The bulkof the refrigerant will leave the condenser as a high pressure liquid andit is then piped to the expansion valve - and the cycle recommences.


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THE BASIC COMPONENTS OF A CIRCUIT


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THE BASIC COMPONENTS OF A CIRCUIT

Compressor

Used to convert low pressure refrigerant in vapour form into a high

pressure gas and to circulate the refrigerantEvaporator

The coldest part of the system. Constructed from tubes or passages,which will be fitted inside a refrigerator of freezer to remove heat from

the contents. In air conditioning units the air being cooled will passover these tubes or coils.

Condenser

The tubes or matrix which are fitted outside of the cabinet of a fridge

or freezer which release heat into the surrounding atmosphere. Thecondenser can dissipate the heat by simple convection or is fanassisted. Large -units may have water cooled condenser systems.

Capillary


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p y

A very thin tubes which causes a restriction in the system between thehigh and low-pressure sides. Capillaries are only used on domestic orsmall, fixed capacity, units.

Expansion Valve

The valve that is used on larger industrial plant in place of the capillary.It serves the same purpose i.e. it controls the pressure in the evaporator.Unlike the fixed dimensions of the capillary, the degree of opening ofthe expansion valve can be adjusted either manually or automatically tomeet varying demands on the system.

Dryer

A container full of a material which will absorb any moisture whichmay have got into the refrigerant. This is essential as the water wouldfreeze and could cause a total blockage to the refrigerant flow. Aseparate dryer should be used in the charging line to treat 'new'refrigerant.


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Accumulator

A large capacity section of tube, container or even a small tank. Its

purpose is to collect any refrigerant liquid which did not completelyevaporate in the evaporator. Any liquid entering the compressor couldcause serious damage. A feed line from the compressor outlet is oftenused to warm the accumulator and so vaporise any liquid refrigerant.

Suction Line

The pipe from the evaporator to the compressor. Also called the 'lowside' line.

Discharge Line

The line from the compressor to the condenser. Often called the 'highside' line.

All air conditioning systems must have four basic elements


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All air conditioning systems must have four basic elements

1. COMPRESSOR

2. CONDENSOR

3. EXPANSION VALVE

4. EVAPORATOR

From the compressor, high-pressure gas is sent to the condenser,wherethe heat is dissipated and condensed to a liquid. The high-pressureliquid flows on to the expansion valve, where it is metered and it's

pressure is reduced. It then evaporates to gas. The cycle is thenrepeated, starting at the compressor.


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COMPRESSOR


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COMPRESSOR

The purpose of the compressor is to circulate the refrigerant in thesystem under pressure, thus concentrating the heat it contains. At the

compressor the low-pressure gas is changed to high-pressure gas.This pressure build-up can only be accomplished by having arestriction in the high-pressure side of the system. This is a smallvalve located in the expansion valve. The metered orifice will servethe purpose for our basic system.

The compressor has reed valves to control the entrance and exit ofrefrigerant gas during the pumping operation. These must seat firmly.For instance, an improperly seated intake reed valve can result in gasleaking back into the low side during the compression stroke, thusraising the low side pressure and impairing the cooling effect.Likewise, badly seated discharge reed valve can allow condensing orhead pressure to drop as it leaks past the valve, lowering theefficiency of the compressor.


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Some independent air conditioning manufacturers still use servicevalves having shut-off valve built in. However, many factory airconditioning systems now use only Shrader valves. The gauge hoses

are still connected to the Shrader valve fitting, in which a valve isincorporated to hold in the refrigerant when a test hose is notconnected to it.

Two service valves are located near the compressor as an aid inservicing the system. One services the high side, and one is used forthe low side. A fitting is provided on each for attaching the test gaugehoses for testing the system. The smaller discharge hose routed to thecondenser, while the low side comes from the evaporator, and is

larger than the discharge hose quickly identifies the high side servicevalve.


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'I'he service points on the typical compressor are as follows:


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I he service points on the typical compressor are as follows:

Replaceable carbon-type seal on compressor shaft.

Gasket at opposite, or oil pump, end of unit,

Serviceable reed valves and head gasket.

Any other internal failure usually requires the replacement

of the compressor.However, some compressors are completely serviceable.

The compressor is normally belt-driven from the enginecrankshaft. Most manufacturers use a magnetic-type clutchwhich provides a means of stopping the pumping of thecompressor when refrigeration is not desired.

COMPRESSOR RELIEF VALVE


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Some compressors have a relief valve for regulating pressure. If thesystem discharge pressure exceeds rated pressure, the valve willopen automatically and stay open until the pressure drops. Thevalve will then close automatically. If the relief valve opens, some oilmay be ejected through the valve. Correct any condition that wouldcause this valve to open.

SUPERHEAT SHUTOFF SWITCH

A superheat shutoff switch stops the compressor when acombination of compressor suction pressure and the compressortemperature is too high. This prevents possible damage to thecompressor from lack of refrigerant oil. The switch is mounted in therear head of the compressor. It senses refrigerant pressure in thelow side of the compressor. The superheat shutoff switch is a

mechanical switch sensitive to both temperature and pressure. Anelectrical contact, welded to the diaphragm contacts the terminalwhenever there is low refrigeration pressure or high temperature inthe compressor inlet. This stops the compressor as explained next.


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The purpose of the condenser is to receive the high-pressure gas


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from the compressor and convert this gas to a liquid . It does it byheat transfer, or the principle that heat will always move from awarmer to a cooler substance. Air passing over the condenser coilscarries off the heat and the gas condenses. The condenser often lookslike an engine radiator.

As the compressor subjects the gas to increased Pressure, the heatintensity of the refrigerant is actually concentrated into a smaller

area, thus raising the temperature of the refrigerant higher than theambient temperature of the air passing over the condenser coils.Clogged condenser fins will result in poor condensing action anddecrease efficiency. A factor often overlooked is flooding of thecondenser coils with refrigerant oil Flooding results from adding toomuch oil to the system. 0il flooding is characterised by poorcondensing action, resulting in increased head pressure, and a high

pressure on the low side. This combination always results in poorcooling from the evaporator.

EVAPORATOR


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The evaporator works the opposite of the condenser, for here refrigerantliquid is converted to gas, absorbing heat from the air in thecompartment. When the liquid refrigerant reaches the evaporator its

pressure has been reduced, dissipating its heat content and making muchcooler than the fan air and reach its low boiling point rapidly. Therefrigerant then vaporises, absorbing the maximum amount of heat Thisheat is then carried by the refrigerant from the evaporator as a low sideof the compressor, where the whole refrigeration cycle is repeated.

The evaporator removes heat from the area that is to be cooled. Thedesired temperature of cooling of the area will determine if refrigerationor air conditioning is desired. For example, food preservation generally

requires low refrigeration temperatures, ranging from 40 oF (4 oC) to below O oF (o18'C).


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A higher temperature is required for humancomfort. A larger area is cooled, which requires that

large volumes of air be passed through theevaporator coil for heat exchange. A blower

becomes a necessary part of the evaporator in theair conditioning system. The blower fans must notonly draw heat-laden air into the evaporator, butmust also force this air over the evaporator fins andcoils - where it surrenders its heat to the refrigerant- and then forces the cooled air out of theevaporator into the space being cooled.

PROBLEMS OF FLOODED STARVED EVAPORATOR


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COILS.

Changing the state of the refrigerant in the evaporator coilsis as important as the air flow over the coils. Liquidrefrigerant supplied to the coils by the expansion valveexpands to a vapour as it absorbs heat from the air. Someliquid refrigerant must be supplied throughout the total

length of the evaporator coils for full capacity.A starved evaporator coil is a condition in which not

enough refrigerant has been supplied through the total coillength. Therefore, expansion of the refrigerant has not

occurred through the whole coil length, resulting in poorcoil operation and too-low heat exchange.

A flooded evaporator is the opposite of the starved coil.


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Too much refrigerant is passed through the evaporatorcoils, resulting in unexpanded liquid passing into the

suction line and into the compressor. Liquid refrigerant inthe compressor can result in damage to the reed valves and

pistons. A flooded evaporator will contain too manyrefrigerants for efficient heat absorption in the evaporatorcoil. The result is lack of evaporator cooling.

Gauge pressure readings on the low side of the systemreadily indicate either condition.

A starved coil is shown by too-low a reading on the

compound gauge plus a too-quick frost formation on thefins. Also, too little air is emitted from the evaporator.

A flooded coil is indicated by too high a pressure on the


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A flooded coil is indicated by too high a pressure on thecompound gauge and excessive sweating of the evaporatorcoils and suction hose. This is accompanied by littlecooling from the evaporator.

The basic system we have discussed will work okay under

constant loads or until the unit ices up because of too muchhumidity. The cooling rate of the evaporator can becontrolled to a great extent by varying the speed of the fan.However, adding other features will aid in operation of thesystem. Lets look at several of the extra controls, startingwith the receiver-dryer (dehydrator).

USE OF SCREENS IN THE SYSTEM


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At any time a refrigeration system is opened for service, foreignmatter can enter in the form of dirt and moisture. These are callednoncondensibles and have a deteriorating effect on Refrigerant - 12 orany other refrigerant. Moisture mixed with refrigerant causeshydrolizing action, which results in interior corrosion of all metal

parts. This corrosion will in time, sluff off into the system in small particles which can stop the flow of refrigerant through the smallorifice in the expansion valve.

Screens are installed throughout the system to filter and hold theseforeign particles from circulating in the system. A filter screen isalways located in the receiver-drier. Should any of these screenscollect foreign particles until they can no longer pass refrigerant,refrigerant flow will stop at this point.

REMEMBER: FROST WILL FORM AT THE POINT OFBLOCKAGE OF THE REFRIGERANT.

WHAT HAPPENS WHEN REFRIGERANT IS


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WHAT HAPPENS WHEN REFRIGERANT ISBLOCKED

A restriction or stoppage of refrigerant flow will cause thefollowing:

1. Normal or low head pressure with low suction pressure.

2. Excessive coolness or frosting of the dehydrator,expansion valve, and compressor service valve.

3. Little or no cooling from the evaporator.


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OPERATION


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When the system is operating properly, the lines should be at thefollowing general temperatures to the touch:

Suction Line - Cool

Discharge Line - Hot

Liquid Line - Warm

Hot Gas Bypass Line - Warm to hot (when bypassingrefrigerant)

DIAGNOSIS


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Restrictions or kinks in the refrigerant lines may beindicated as follows:

Suction line - low suction pr essur e at the compressor,low discharge pressure. L ittl e or no cooling.

Discharge line - compressor relief valve opens.

Liquid line - low discharge pressur e, low suctionpressure, no cooling.

Hot gas bypass - low suction pressure, possibleevaporator icing.


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The Refrigerants most commonly used in domestic, commercial andindustrial systems are the following:


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R11 Employed with centrifugal compressors for air conditioning systems,as a secondary Refrigerant and also as a solvent.

R12 Until recently the most widely used for high, medium and lowtemperature Applications.

R13 Used for ultra-low temperature applications

R22 Used in commercial and industrial low temperature systems and insome domestic Appliances.

R113 Used mainly in comfort air conditioning systems with centrifugalcompressors

R500 Azeotropic mixture of R12 (73.8%) and R152 (26.2%) - substitutionfor RI 2 Can increase compressor capacity

R502 Azeotropic mixture of R22 (48.8%) and RI 15 (51.2%) - developed forlow Temperature applications to replace R22.

R717 Ammonia has higher refrigerating effect per unit capacity than anyother refrigerant - Used in large industrial systems

The installation or service engineer should be able to identify


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refrigerants by the cylinder base colour and associated label colour, or by the cylinder base colour and the colours of the bands located

around the top of the cylinder. The cylinder colour codes for therefrigerants listed above are given in table below..

H ANDL I NG REF RI GERANTS


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Refrigerants must be handled with care to avoid danger.

Do not discharge refrigerant into the atmosphere. Suitable recoveryand recycling equipment must be used.

Liquid refrigerant, if allowed to strike the eye, can cause blindness.If allowed to strike the body can cause frostbite.

If a refrigerant container is heated, or contacts a heating element, the pressure inside can build up and explode the container.

If refrigerant is allowed to contact an open flame or heated metal, a poisonous gas will be created. Inhaling this gas can cause you to become violently ill. Remember - refrigerant can he dangerous. Itshould only be handled by a trained service technician.


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COMPOUND GAUGE (LOW SIDE)

The compound gauge derives its name from its function. It will register


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p g g g both pressure or vacuum. All air conditioning systems can, under certainconditions, drop from a pressure into a vacuum on the low side. It is

necessary that a gauge be used that will show either pressure (psi and kPa)or inches of mercury vacuum (Hg.).

The vacuum side of the gauge must be calibrated to show 0 to 30 inches (0to 762mm) Hg. The pressure side of the gauge must be calibrated toregister accurately firom 0 pressure to a minimum of 60 psi (414 kPa). The

maximum reading of the pressure should not exceed 160 psi (1 103 kPa).Practically all readings of the low side of the system will be less than 60 psi(414 kPa) with the system in operation.

The scale reading preferred by the individual serviceman is left to his ownchoice. To accurately convert pressures to temperatures in the system, the

gauge should be calibrated to a low enough scale that it will not be difficultto obtain an accurate reading. The higher the pressure scale, the moredifficult it becomes to get an accurate pressure temperature conversion.

HIGH PRESSURE GAUGE (HIGH SIDE)


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The high pressure gauge is used to determine pressures in the highside of the system. The gauge is calibrated to register accurately

from zero pressure to a minimum of 300 psi (207OkPA0). A fewsystems operate under high head pressure during normal operationconditions. This is why the high pressure gauge should have areading of at least 600 psi (4140 kPa).

GAUGE MANIFOLD

The gauge manifold mounts the high and low side gauges andconnects the gauges into the high and low sides of the system bymeans of test hoses. The gauges connect to the upper part of themanifold through holes drilled and tapped into a 1/8 - inch pipethread. Test hose connectors below the gauges on the lower side ofthe manifold direct from the refrigerant through the manifold to thegauges to obtain pressure readings.

By opening and closing the hand valves on the manifold,f


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the following jobs can be done:

1) Recovering excess refrigeration from the system2) Bleeding air from the hoses

3) Recovering refrigerant before service work

4) Removing air and moisture during pump-down5) Filling system with refrigerant

IMPORTANT: Do not release refrigerants to the atmosphere.Use a suitable recovery system.


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LEAK DETECTORS

Several types of leak detectors are available to the serviceman:


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1. Coloured Dye Additive

2. Liquid Detergent - Type Detector

3. Electronic Leak Detector

4. Propane Torch Detector

A COLOURED DYE ADDITIVE is available which is addedto the refrigerant. Operation of the system will showcolouration at the point of leakage. A very slight leakrequiring several weeks or even months to bleed off enoughrefrigerant to effect the system cooling can often be locatedusing this additive when other methods of leak detection fail.

A LIQUID DETERGENT -TYPE DETECTOR may be used aroundconnections and any external point that might be the source of leak forthe Refrigerant- 12 Escaping refrigerant will cause the liquid to bubble


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the Refrigerant 12. Escaping refrigerant will cause the liquid to bubble,indicating a leak. Any parts that are not accessible, such as coils in the

condenser and the evaporator, cannot readily be coated with this liquid tocheck for leaks.

The ELECTRONIC LEAK DETECTOR is a sensitive leak detector.Most electronic detectors can detect an equivalent of 1/2oz. per year.However, the initial cost of this type of detector has been a deterrent toindividuals and small shops doing a minimum of air conditioningservice. This instrument is electronic and must be handled with care togive accurate results. When cared for properly, the electronic detectorwill locate leaks quickly and accurately that are almost impossible tolocate with other types of detectors.

The PROPANE TORCH LEAK DETECTOR is the most


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The PROPANE TORCH LEAK DETECTOR is the mostfamiliar and has received the most widespread use

because of its case of handling, availability of propane indisposable tanks, and low initial cost. In operation, the

blue flame changes colour to yellow or vivid purplish bluewhen Refrigerant- 12 is picked up by the sniffer tubeoutside the system.

! CAUTION: The propane torch leak detector must only beused in well ventilated areas. When Refrigerant 12 passesover an open flame, it gives off phosgene gas, which is verytoxic. Do not breathe fumes given off by the detector.


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VI SUAL I NSPECTI ON OF SYSTEM

Visually inspect the following:


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Visually inspect the following:

1. COMPRESSOR DRIVE BELTS TIGHT; NOT WORN ORFRAYED; AND ALIGNED WITH PULLEYS . The compressor

belt is subjected to a heavy load during operation. This is especiallytrue when the head pressures build up in excess of 200 psi(138OkPa) in hot weather operation. The belt must be in excellentcondition to withstand the strain of heavy loads. If the pulleys are

not properly aligned, extreme wear to the belt and pulleys will result.Too tight a belt tension will result in strain to the bearings of unitsoperated by the compressor belt. Too loose a belt tension will resultin belt slippage and poor performance. A belt tension gaugeeliminates guess work in tightening the compressor belt. If a belt

tension gauge is not available, tighten until there is 318 to 1/2 inch(10-13mm) deflection between any two pulleys that are farthestapart.

2. COMPRESSOR BRACKETS AND BRACES TIGHT ANDNOT CRACKED OR BROKEN . Mounting bolts work loose, and


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brackets often break under the vibrations and strain of operation.Failure to inspect and repair any damage at these points can result inearly system failure.

3. HOSES OR COPPER LINES NOT CHAFING ORLEAKING . Grommets and rubber pads that were originallyinstalled to protect the hoses from contact with metal parts maydeteriorate or loosen. Exposing the hose or line to constant rubbingand chafing can cause deterioration and allow the refrigerant toescape. To prevent damage, install some type of protective material.

4. CONDENSER CLEAN AND PROPERLY MOUNTED .Insects and dirt clog the condenser and radiator and stop air

movement. Any blocking of full air flow over the condenser andradiator coils must be corrected to allow proper condensing action ofthe system.

5. EVAPORATOR CLEAN . The evaporator condenses moisturewhich in turn traps dust and lint on the side where the air enters.Th bl f b ff i l h h


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The blower or fan can be effective only when the evaporator passages are clear. Dust and lint should be removed.

6. COMPRESSOR OIL LEVEL CORRECT . Most compressorsdo not have a provision to check the oil level without disconnectingthe compressor from the system. Make an oil check only with thesystem discharged. Do not overfill the system with oil as floodingof the condenser and evaporator will result.

7. AIR DUCTS AND LOUVRES OPERATING SMOOTHLY .Operate all mechanisms to check for free operation without bindingand sticking.

8. BLOWER MOTOR OPERATING SATISFACTORILY .Operate blower motor at all speeds. If motor is noisy or fails atsome speeds, repair it.

9. AIR FILTERS CLEAN . Many systems use a fresh air andi l i fil l h i b f i i h


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recirculating filter to clean the air before it goes into the evaporatorcoil. The filters must be removed and cleaned,- as a clogged filterwill seriously affect evaporator air flow.

10. VISABLE LEAKS . A small oily spot usually indicates arefrigerant leak, as oil is carried out with the escaping refrigerant.

11. LEAK TEST THE SYSTEM . A leak test will tell whether an

oily spot indicates a leak. This test can only be performed onsystems that are operative. A unit that has lost its refrigerant must

be partially charged before this test can be performed.

MOISTURE IN SYSTEM

Any air conditioning system should be dry as it is possible to


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Any air conditioning system should be dry as it is possible tomaintain it. The refrigerant has had virtually all the moisture

removed from it during manufacture. Any moisture introduced intothe system must come from outside sources such as a break in a lineor from improper sealing of connections when a unit is removed forservice.

Refrigerator- 12 will absorb moisture readily when exposed to it.. Tokeep the system as moisture-free as possible, all systems use adehydrator containing a desiccant which can absorb great quantitiesof moisture. However, each can only absorb a predetermined amount,and when the saturation point has been reached, the effectiveness islost.


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Documents

Refrigeration and Air Conditioning Principles