air condition and refrigeration detailed.pptx

Simple and detailed refrigeration system

1. Refrigeration & Air conditioning – PART 1 By Malaka Udayanga By Malaka Udayanga

2. Refrigeration vs AC vs ventilation

3. Basic refrigeration cycle

4. Refrigerant behavior Most refrigerant vapors have similar characteristics and properties to steam except that they have a much lower boiling point Critical Temperature….? latent heat , energy absorbed or released by a substance during a change in its physical state (phase) that occurs without changing its temperature. The saturation temperature is just the official name  for the boiling point.

5. Isothermal vs Adiabatic

6. ENTHALPY VS ENTROPY VS HEAT Heat  is always the energy in transit , i.e , the energy which 'crosses' the system boundaries. Whereas  Enthalpy  refers to total  heat   content in a system

7. Vapor compression cycle A-B, Isobaric Heat absorption in the evaporator B-C , Isentropic compression in the compressor (frictionless adiabatic compression in ideal cycle) C-D , Isobaric Heat removal in condenser D-A , Constant enthalpy(Isenthalpic) expansion in expansion valve Heat energy equivalent of work done = Heat energy rejected- heat energy received= Area ABCDA + Area under AD Coefficient of performance = heat energy received/ Heat energy equivalent of work done The coefficient of performance for freon is about 4.7

8. Refrigeration thermodynamic cycles Heat energy received from cold chamber = area under AB. Heat energy rejected in the condenser = area under CD. Heat energy equivalent of work done = heat energy rejected heat energy received = area under CD-area under AB = area of figure ABCDA + area under throttle curve DA.

9. Refrigeration thermodynamic cycles Sub Cooling there is a loss in refrigeration effect due to flash off to vapor when the liquid is being throttled through the expansion valve. Undercooling before the expansion valve reduces flash off after throttle, so lowering quality, and increasing refrigeration effect in the evaporator. Critical Temperature Is that temperature beyond which the gas cannot be liquefied by isothermal compression, i.e. as a gas, no amount of compression will liquefy if the temperature remains above the critical temperature for that substance

10. Desirable Properties of a Refrigerant 1 .Low boiling point (otherwise operation at high vacuum becomes a necessity). 2. Low condensing pressure (to avoid heavy machine and plant scantlings and reduce the leakage risk). 3.High specific enthalpy of vaporization (to reduce the quantity of refrigerant in circulation and lower machine speeds, sizes, etc.). 4.Low specific volume in vapour state (reduces condenser size and increases efficiency). 5.High critical temperature (temperature above which vapour cannot be condensed by isothermal compression). 6.Noncorrosive and non solvent (pure or mixed). 7.Stable under working conditions. 8.Nonflammable and nonexplosive (pure or mixed). 9.No action with oil (the fact that most refrigerants are miscible may be advantageous, i.e. removal of oil films, lowering pour point, etc., provided separators are fitted). 10.Easy leak detection. 11.Non toxic (non poisonous and non irritating). 12.Cheap, easily stored and obtained.

11. Refrigerant Types – IMO Guideline No one refrigerant will have the best of all the properties mentioned in above section. A refrigerant selected for a particular use will have the best mix of properties for that application. Refrigerants that contain chlorine, (known as CFC’s and HCFC’s), if released into the atmosphere, cause damage to the environment. This includes: • depletes the ozone layer, thus allowing harmful ultra violet radiation to enter the earth’s atmosphere; and • Contributes to global warming (greenhouse effect) by trapping the heat being reflecting away from the earth, thus increasing the earth’s temperature. These refrigerants are being gradually being replaced with less harmful refrigerants. MARPOL, Annex VI (Regulation 12 – the use of ozone depletion substances (ODS) in marine applications). New installations containing CFC or Halon are not permitted on ships constructed on or after 19 May 2005, while new installations of HCFC equipment is prohibited after 1 January 2020, both on new and existing ships. Furthermore, it is prohibited to deliberately discharge ODS to the atmosphere; these refrigerants should be collected in a controlled way and be either reused on board or sent to an appropriate facility (IMO, 2017b). The GWP of refrigerants is not constrained by any IMO mandatory requirements, thus there are no restrictions for using HFCs on board ships.

12. Main refrigerant types 1. Chloro-Fluoro-Carbons (CFC)   contains carbon, chlorine, and fluorine atoms; atmosphere lifetime between 60 to 540 years; ozone depleting; Include R11 and R12, ( ie . Freon 11 and Freon 12); and Phased out by 1 st January 1996. 2. Hydro-Chloro-Fluoro-Carbons (HCFC)   contains hydrogen, carbon, chlorine, and fluorine atoms; atmosphere lifetime between 2 to 22 years; comparatively low ozone depleting; includes R22, (Freon 22); and Phased out by 2020.   3. Hydro-Fluoro-Carbons (HFC’s)   contains hydrogen, carbon, and fluorine atoms; not ozone depleting; Includes R-32, R- 125, R134a, R-143a, and R-15 2a 4. Inorganic includes ammonia, water (R718), CO 2 , and air; and Not ozone depleting.

13. Main refrigerant types Under Regulation 12, calls for all ships to maintain a list of equipment containing ozone depleting substances (ODS) and an ODS record book. The regulation covers the recording of ODS use, deliberate and non-deliberate emission of ODS and the disposing of equipment containing ODS from ships. The purpose of this ODS data recording is to keep a record of the condition and quantities of ODS on board a ship and serves as the basis for data collection by the relevant Flag State. Ozone depleting substances that may be found on board ships include but are not limited to: Halon 1211 Halon 1301 Halon 2402 CFC-11 CFC-12 CFC-113 CFC-114 CFC-115     Existing systems and equipment using ODS are permitted to continue in service and may be recharged as necessary. However, the deliberate discharge of ODS to the atmosphere is prohibited. Maintenance, servicing and repair work shall be carried out without releasing any substantial quantity of refrigerant. When servicing or decommissioning systems or equipment containing ODS the gases are to be duly collected in a controlled manner and, if not to be reused onboard, are to be landed to appropriate reception facilities for banking or destruction. Any redundant equipment or material containing ODS is to be landed ashore for appropriate decommissioning or disposal. The latter also applies when a ship is dismantled at the end of its service life. These substances, when removed from ships, must be delivered to reception facilities As per Annex VI , Regulation 12:- Ozone Depleting Substances (ODS)

14. Main refrigerant types Records and documents to be maintained:- a) A list of equipment containing ODS should be maintained. b) If the ship has any rechargeable system containing ODS, then an ODS record book should be maintained. This record book shall be approved by administration. c) Check for gas leaks to be carried out regularly and recorded. d) Entries in ODS record book shall be recorded in terms of mass ( kg) of substance in respect of- • Recharge of equipment • Repair or maintenance • Discharge of ODS to atmosphere either deliberate or non-deliberate • Discharge of ODS to land based facilities • Supply of ODS to ship Every ship must carry recover unit to collect the gas in case of any maintenance

15. Refrigeration system Assume that the rooms are all warm and the compressor is running with all the solenoid valves open supplying refrigerant to the respective expansion valve and evaporator. Should one or two rooms be down to temperature the solenoids close thus reducing the volume of gas returning to the compressor. The suction pressure drops and the compressor unloads. If more rooms shut down then the suction pressure will drop to cut out point and the compressor will stop. When the rooms warm the solenoids open again, refrigerant passes back to the compressor, the suction pressure rises and compressor starts. With more rooms opening, the suction pressure increases and the compressor loads up more cylinders.

16. Thermostatic expansion valve- The purpose of this valve is to efficiently drop the pressure of the refrigerant. It achieves this by passing the liquid through a variable orifice giving a constant enthalpy pressure drop. The refrigerant at lower pressure has a corresponding lower boiling point (saturation temperature). Undercooling in the condenser increases the efficiency of the plant by allowing more heat to be absorbed during the vaporization process. In addition, it also reduces the internal heat absorption process that occurs during the expansion stage which is due to a small degree of flash of f as latent heat (of vaporization) is absorbed from surrounding liquid to reduce the temperature of the bulk liquid to the new corresponding saturation temperature for the reduced pressure.

17. Thermostatic expansion valve The expansion process is controlled by the action of the bellows and push pins acting on the orifice valve plate. The bellows is controlled by a bulb which measures the temperature of the gas at outlet from the evaporator. To ensure no liquid passes through to the compressor, the expansion valve is set so that the gas at outlet from the evaporator has 2 to 3 degrees of superheat. The common TEV works on the assumption that the pressure at the outlet of the evaporator is the same as the pressure at the inlet of the evaporator. Since the pressure at the outlet is lower, then saturation temperature is also lower and the refrigerant tend to vaporize completely; before it gets to the evaporator outlet: thus, the latter part of the evaporator becomes ineffective. To overcome this problem a externally equalized TEV is installed on systems that have large pressure drops across the evaporator A capillary tube runs from just after the superheat sensing bulb, back to the underside of the TEV diaphragm, so that the pressure Of the refrigerant at the inlet to the evaporator does not act on the diaphragm .

18. Back pressure regulator valve This valve is fitted to the higher temperature rooms, vegetable and flour (+5oC) only and not to the Meat and Fish rooms (-20oC). They serve two main purposes. Firstly when all solenoid valves are opened, they act as system balancing diverters , that is they restrict the liquid flow to the rooms which can be kept at the higher temperature and deliver the bulk to the colder rooms. Secondly they serve to limit the pressure drop across the expansion valve by giving a set minimum pressure in the evaporator coil. This in turn limits the temperature of the refrigerant thereby preventing delicate foodstuffs such as vegetables from being damaged by having air at very low temperatures blown over them. Ultimately, they may also be set to provide a safety limit to the room temperature by restricting the pressure to give a corresponding minimum saturation temperature of 0oC.

19. Oil Separator The purpose of the oil separator, situated on the compressor discharge line, is to return oil entrained in the gas, back to the compressor sump. The oil return may be float controlled as shown, electric solenoid controlled on a timer, or uncontrolled with a small bore capillary tube allowing continuous return. With all of these methods a shut off valve is fitted between separator and compressor to allow for maintenance. The oil gas mix enters the separator where it is made to change direction, the heavier oil droplets tend to fall to the bottom.

20. Sight Glass Often of the Bulls eye form. This allows the operator to ensure that it is only liquid, and not a liquid/gas mix going to the expansion valves. On some designs a water indicator is incorporated, this is a coloured ring in contact with the liquid, when water is detected it changes colour , typically from pink to blue. Filter Drier Can be either a compacted solid cartridge or bags of dessicant . The main purpose of this unit is to remove the moisture from the refrigerant. Moisture cause two main problems. Firstly it can freeze to ice in the evaporator and cause blockage. Secondly it can form acids by reaction with the freon refrigerants. This acid attacks the copper in the lines and deposits its in other parts of the system. This can become particularly troublesome when it is deposited on the compressor mechanical seal faces leading to damage and leakage. Fine particles which could possible block the expansion valve are removed. System components

21. Thermostat and Solenoid Valve These two elements form the main temperature control of the cold rooms. The Thermostat is set to the desired temperature and given a 3-to-4-degree differential to prevent cycling. When the temperature in the room reaches the pre-set level the thermostat switch makes, and the room solenoid is energized allowing gas to the refrigerant liquid to the expansion valve. A manual override switch is fitted as well as a relay operated isolating contact which shut the solenoid when the defrost system is in use. Condenser Generally, a water-cooled tube cooler. A safety valve and vent are fitted. The purpose of the vent is to bleed off non- condensibles such as air which can enter the system when the suction pressure is allowed to fall below atmospheric or can be contained within the top up gas. The presence of non- condensibles is generally indicated by a compressor discharge pressure considerably above the saturation pressure of the refrigerant. The coolant flow to the condenser is sometimes temperature regulated to prevent too low a temperature in the condenser which can affect plant efficiency due to the reduction in pressure. Below the condenser, or sometimes as a separate unit, is the reservoir. Its purpose is to allow accurate gauge of the level of refrigerant in the system. In addition to this it also allows a space for the refrigerant liquid when the system is 'pumped down'. This refers to the evacuation of the refrigerant gas to the condenser to allow maintenance on the fridge system without loss. For systems not fitted with a reservoir, a sight glass is sometimes incorporated on the side of the condenser. Care should be given to ensuring that the liquid level is not too high as this reduces the surface area of the cooling pipes available for condensing the liquid and can lead to increased discharge pressures. System components

22. Capacity control or regulation in refrigeration compressors enables the refrigeration plant to run at part loads according to the demand of the refrigerant in the system. Capacity control is obtained when the solenoid valve, fitted in the top cover, closes the access to the two cylinders, positioned under the same top cover. This makes the inlet pressure to the cylinder drop to zero bar. At the same time the compressor capacity is reduced to 50%. However, a little gas will be flowing through the closed solenoid valve, hereby ensuring the necessary cooling and lubrication of the cylinders. This capacity control permits a certain reduction in power consumption. System components Capacity control valve (A) Controlled operation: With the solenoid valve energized, the suction port in the corresponding cylinder head is shut off by means of a servo valve; the pistons of this cylinder row run idle without gas pressure. (B) Normal operation: With the solenoid valve de-energized, the gas ports in the valve plate and cylinder head are open.

23. System components Capacity control valve A spring piston is provided which controls the spreading of high-pressure oil supply into the bore chamber. The spring piston is pressed by the oil supplied through an orifice which pushes the piston and aligns the un-loader holes, providing high-pressure oil to the unloader unit. The un-loader assembly comprises a un-loader piston held by a spring. The un-loader piston is connected to a rotating cam ring having lifting pins attached to the suction valve. The lifting pins always act on the suction valve i.e. un-loading the unit at stop condition. When the bores on control valve align with the unloader bores, oil will pass and press the un-loader piston rotating the cam and releasing the un loader pins from the suction valve

24. At a star-delta start of electric motors it is often considered necessary to limit the compression work of the machine at the starting moment in order to reduce the starting torque of the electric motor. Usually, a solenoid valve is used in a by-pass arrangement which in the starting up phase short circuits the discharge side to the suction side of the compressor. At the same time, a non-return valve must be fitted in the discharge line to the condenser preventing the return flow of discharge gas to the compressor. When the electric motor has reached its max. number of revolutions per minute, a switch takes place from star to delta start. The solenoid valve is closed, and the compressor now works under normal conditions. System components Refrigeration Compressor Starting Unloader

25. It should be noted that for this design the carbon seal and flexible bellows is fixed in way of the mounting plate and the hard running surface is allowed to rotate. This is the opposite of the set up for seals mounted on pumps. The finish of the running surface of the seal is extremely fine. However, in extenuating circumstances i.e. when the surface has been damaged say by the deposit of copper, it is possible to lap the face of the carbon. The method would recommend is metal polish such as brasso , on a true flat surface on which is laid chart paper. The chart paper absorbs the wear particles as they are removed and a reasonable finish is possible. System components Shaft oil seal

26. Safety devices High Pressure Cut Out High pressure can be caused in a refrigeration plant due to various causes like over charge, loss of cooling water, high ambient temperature, air, or other incompressible gases in the system, and obstruction in the discharge line of the compressor For protecting the compressor from high pressure and subsequent failure, a high pressure cut out is provided that take a pressure tapping from the discharge line and when it detects an over pressure, it stops the compressor. The HP cut out is not resettable automatically but has to be reset manually by the operator. This is because the high pressure is a serious fault and the cause must be investigated and corrected before the plant is started again.

27. Safety devices Low Pressure Cut Out To protect the compressor against low pressure in the system and to avoid the ingress of air into the system if a vacuum is generated in the lines a low pressure cut out is provided. Also when the refrigerated compartments are cut off by the solenoids and there is no return gas, the low pressure cut out is activated. When the solenoid of the refrigerated compartments open, the return gas comes in the inlet of the compressor and the suction pressure rises, and then the low pressure switch cuts in the compressor. Unlike the high pressure cut out, the low pressure cut out is self-resettable and does not need to be reset manually

28. Safety devices Oil Pressure Cut Out When the compressor starts, the oil pressure rises to the cut-in point of the switch. The differential switch will open and break the circuit to the heater, and the compressor will operate normally (see Figure 90). If the useful pressure does not rise to the cut-in point within the time limit (60 to 180 seconds), the differential switch contacts will not open and the heater will stay in circuit. This causes a bimetal strip in the timing relay to warp and open the timing contacts, which will break the circuit to the starter coil and stop the compressor. Similarly, if the useful pressure falls below the cut-in point during operation, the differential switch will close and energize the heater. The timing relay will stop the compressor after the time delay characteristic of the switch. Controls are available with 60 and 90 seconds delay, but it must be realized that the time is not variable.

29. The relief safety head, and safety spring is fitted to allow the complete delivery valve assembly to lift in the event of liquid carry over to the compressor. Unloading arrangements are fitted so that the motor driving the compressor is not overloaded by a high initial starting torque and multi cylinder units can be unloaded during periods of low demand Safety devices The relief safety head

30. Compressor types. There are four main types: reciprocating, rotary, centrifugal and screw. Reciprocating compressors are in the majority in marine applications as they are most suited to low specific volume vapors and large pressure differentials, characteristics of all the main refrigerants. Reciprocating Almost all modern machines are motor driven, high speed (up to 30 rev/s) single acting types which have adopted many improvements in line with the automobile industry. Pistons are usually of the trunk type, two or three compression rings and a lower oil seal ring, the suction valve may be in the head of piston or in the cylinder head, the most modern arrangements have the suction and discharge valves in a valve plate in the cylinder head. Compressor bodies are close grained castings of iron or steel. The crankshaft can be eccentric drive.

31. Compressor types. Reciprocating continued.. Provision is made for reducing the capacity of the machine either manually or automatically. Capacity reduction gear lifts and holds open the alloy steel suction valves of a specified number of cylinders, this is operated by oil pressure on a servo piston in the automatic type. This can also provide total or partial un-loading for easier starting. The lubrication should be clear from Fig. Oil is supplied by a rotor type of pump in which the inner rotor has one less tooth than the outer rotor and oil is induced to flow between the two rotors.

32. Compressor types. Rotary Such compressors mainly find application in household and domestic units but modern practice is extending their use to cargo purposes. A variation on the above is a multiblade type whereby the eccentric rotor contains spring loaded blades (or relies on centrifugal force). When any rotary compressor is not in use the oil film between eccentric rotor and cylinder is broken which means pressure equalization and easy starting but requires the fitting of a non return valve in the suction line. To reduce sizes these machines are direct drive from the motor. At the position shown the discharge and suction strokes are half completed, 270°. At 0° discharging at compression stroke, induction at suction stroke. At 90° start of compression and end of suction. At 180" compression taking place and the suction stroke has just started. Thus the leading flank of the rotor acts as the discharger and the lagging flank acts as the inductor.

33. Compressor types. These machines work on a similar principle to the centrifugal pump whereby discharge velocity energy is converted to pressure head. For high pressure differentials, as normally exist, a series of impellers are required on a fast running rotor, each impeller feeding to the next in series to build up pressure. These machines are best suited to low differential pressure, high volume capacity work such as air conditioning. Capacity reduction is affected by directional blades at the rotor inlet port. Efficiency is increased if interstage flash vapor formed during liquid expansion is returned to an appropriate stage of the compressor. Centrifugal

34. Compressor types. Screw These compressors can be visualized as a development of the gear pump. A male rotor with say four lobes on the shaft, meshes with a female rotor of say six lobes on a parallel shaft. Clearance between lobe screws and casing is kept to a minimum with sealing strips and oil film. As the space between two adjacent lobes of the female rotor passes the inlet port at one end of the compressor a volume of gas is drawn in. With rotation, a lobe of the male rotor progressively fills this space so compressing the vapour and, due to the helical screws, forces it axially to the outlet port at the other end. To reduce capacity sliding sleeves around the barrel can be moved axially to bring the outlet port nearer to the inlet port.

35. Compound gauge. A number of pressure gauges and thermometers are used in refrigeration systems. The figure shows a compound gauge. The temperature markings on this gauge show the boiling point (or condensing point) of the refrigerant at each pressure; the gauge cannot measure temperature directly. A water pressure gauge is installed in the circulating water line to the condenser to indicate failure of the circulating water supply. Standard thermometers of appropriate range are provided for the refrigerant system. Operating parameters ranges are differ with the refrigerant properties in use.

36. Troubleshooting of refrigeration system Undercharging of Refrigeration System Indication: • Compressor is running hot and performance of the compressor falls off due to high superheat temperature at the suction side of compressor. • Suction and discharge pressure of the compressor is low. • Large vapor bubbles in the liquid sight glass. • Low gauge readings in the condenser. • Ammeter reading for the compressor motor is lower than normal. • Rise in room temperature which is to be cooled. • Compressor is running for extended period of time. Causes: • Leakage of refrigerant at the shaft seal, flange couplings, valve gland etc. • Expansion valve may be blocked at the strainer. • Partial blockage of refrigerant at the filter or drier or evaporator may cause undercharging. Action: • Identify and rectify the leakage of refrigerant from the system. • Clean the filter and drier. • Charge the system with fresh refrigerant as required.

37. Troubleshooting of refrigeration system Overcharge of Refrigeration System Indication: • The liquid level in the condenser is too high (high condenser gauge reading). This will reduce the available condensing surface, with corresponding increase in the saturation (boiling) temperature and pressure. • High pressure switch of the refrigerant compressor activates and stops the compressor. • The suction and the discharge pressures are high. Possible icing of compressor suction Causes: • It may be due to the reason that excessive refrigerant has been charged in the system. • Air in the system may also cause over charging indication. • It may also be due to the formation of ice on the expansion valve. Action: • Remove the refrigerant from the system. This is done by connecting a recovery cylinder to the liquid line charging valve, starting the compressor, and then operating the charging valve. • Purge the air from the system and maintain effective cooling. • Remove ice from the regulator by using any of the defrosting methods.

38. Troubleshooting of refrigeration system Air in the System Indication: • This may cause the refrigeration compressor to overheat, with high discharge pressure and normal condensing temperature • There are possibilities of small air bubbles in the liquid sight glass of the condenser. • Condensing pressure of the refrigerant in the condenser may be high. • If there is excessive air, it may reduce the cooling capacity of the system, making the compressor to run for long. • It may cause the gauge pointer of the condenser to jump indefinitely. Causes: • During charging, air may enter in to the system. • If Freon-12 is used air may leaks in to the suction line because the working pressure of the Freon-12 refrigerant is less than the atmospheric pressure. Action : • Air in the system can be removed by collecting the system gas in the condenser, leaving the condenser cooling water on and venting out the air from the top of the condenser because air will not be condensed in the condenser but remains on top of the condenser above the liquid refrigerant. • Connect the collecting cylinder to the purging line of the condenser, open the valve, and collect air in the cylinder. • After purging the air from the system don’t forget to shut the purging valve. • Check the level of the refrigerant in the system. If required, charge the system with fresh refrigerant. • Restart the compressor with all safety precautions.

39. Troubleshooting of refrigeration system Air in the System -Purging procedure In the normal operation of the system, measure the liquid refrigerant pressure, temperature at the outlet of the condenser/reservoir Check the corresponding saturation temperature for the recorded pressure of the liquid refrigerant from the P-T chart for the same refrigerant Compare the measured temperature with the determined saturation temperature for any sub-cooling and adjust the flow of the cooling water through the condenser to achieve near saturation condition inside the condenser, Then, With the condenser liquid refrigerant outlet valve closed, circulate cooling water, start the compressor and pump down the liquid to the condenser/reservoir, checking the pressure in the suction line. If this pressure is allowed to drop down below the atmospheric pressure, then there could be chances of air ingress into the system. Circulate the cooling water till the cooling water outlet and the inlet temperatures equal, a check to ensure complete pump down operation. Check the condenser sea water outlet temperature, check the refrigerant pressure corresponding to its temperature from the P-T chart of same refrigerant. Collect air from condenser purging line until the satisfactory readings are obtained. Proper recording of th e operation must be made whereas applicable with present regulation under MARPOL Annex VI.

40. Troubleshooting of refrigeration system Oil in the Refrigeration System Indication: • Temperature is not dropping in the cold rooms as normal, due to fact that oil act as insulation in the evaporator. • It may cause excessive frost on the suction line. • Refrigerant compressor runs for the extended period of time. • Lubricating oil level in the compressor will drop. • Refrigerant level will fall if oil has caused blockage. Causes: • This may happen if the oil separator is not working properly. • Oil may carry over from the compressor and may not come back to the compressor due to blockage in the system. • Defective piston rings or worn out liner of the compressor may cause the oil to carry over along with the refrigerant. • Compressor may take high capacity current during starting. Action: • Check the oil separator for proper functioning. • Check the drier for proper cleaning and if its require cleaning clean it • Evaporator coil should be drained to remove any trace of oil. • If there is oil in the cooling coils, increase the condenser and evaporator temperature differentials and remove excess frost on the suction pipe. • Heat pipes with blow torch.

41. Troubleshooting of refrigeration system Moisture in the System This normally comes with the ingress of air in the system. Moisture may freeze at the expansion valve, giving some of the indication of under charging. It will contribute to the corrosion in the system. It may cause lubrication problems and breakdown of the lubricating oil in the refrigerant compressor. Action: • Renew silica gel in case of minor moisture. • Collect refrigerant and remove all air and moisture by vacuum pump if the amount is huge. Flooding of Refrigerant in the System This is seen as liquid getting back to the suction of the refrigerant compressor. It may be due to a faulty or incorrectly adjusted expansion valve and also due to solenoid valve leakage. It may also result from overcharging of the refrigeration system. Flooding may lead to an iced up evaporator.

42. Troubleshooting of refrigeration system Short cycling: Reasons: - * L.P Cut out is defective. * L.P Cut out setting not correct, too low difficult for Cut In. * Lesser gas flow * Less gas in system. * Drier Choked. * Expansion valve filter choked or Expansion valve Malfunction. * Evaporator Choked. * Compressor valves leaking. Actions : - a. Check L.P. cut out setting, cut out pressure OK. b. Check flow of gas by seeing sight glass, which should show full flow of refrigerant. c. If no full flow- either less gas or drier chocked, change the drier. d. Check level in receiver, if low, then charges gas. e. Expansion valve filter choked, then clean it. f. Expansion valve malfunctioning- Change it. g. Evaporator choked- Blow-thru evaporator with nitrogen.

43. Flocculation :- Th e coalescence of a finely divided precipitate into larger particles. Flocculent .- Existing in the form of cloud-like tufts (or flocs). Cooling of Oils can cause a wax to form and precipitate, eventually forming wax crystals. When in the crystal state the wax is defined as a flocculent, the temperature at which this occurs is called the "Floc Point" The floc point is determined by cooling a sample of refrigerant containing 10% oil, the temperature at which the wax precipitates is the floc point. Wax crystals in a refrigerator would have a detrimental effect on expansion valves and must be avoided. In general, paraffin based oils are not used, the naphtha based type being preferred although almost all oifs now are synthetic. Refrigerator oils are de-waxed to achieve a law pour and floc point. The "As new' behavior of a refrigerator oil can be affected if there were any kind of contamination that influences the oil hence if contamination is suspected then the oil should be changed Flocculation

44. Copper Plating. Under some internal operating conditions of refrigeration systems employing halogenated refrigerants, highly polished metal parts of the compressor develop a deposit of copper. Parts which suffer include cylinder walls, pistons, valves, bearings and even seals. Plating is most common on parts that develop heat, such as frictional surfaces and discharge valves. If allowed to accumulate, the deposit may become thick enough to cause binding of moving parts and compressor failure. The copper may emanate from tubing, motor windings (in sealed rotary compressor systems), or any other part of the system made of or containing the metal. Copper is not used in ammonia systems so that plating is not a problem with these systems, Plating does not occur in sulphur dioxide systems, although copper is present. Halogenated refrigerant systems, such as those with Freons and Methyl Chloride, are affected. The reason for copper plating is not fully understood. Oil does dissolve copper, but tests prove that the solution will remain intact unless other influences, such as moisture, are present to cause precipitation. Copper plating will occur on glass surfaces, so that the theory of precipitation by straight electrostatic displacement appears to be unfounded. Theories involving hydrolysis, salts resulting from acid reaction with copper, ironing out of particles resulting from wear, stray electrical currents causing electroplating, and others have all been considered and disproved. It is well established that systems containing moisture are more susceptible to copper plating than dry systems. The problem is less serious in systems containing high quality oils. The answer to the problem of copper plating, then, appears to be one of maintaining a moisture-free system and using only highly refined oil.

45. De-frosting methods Defrosting is process of removing the ice formed on the surface of evaporator. Frost hampers the heat transfer efficiency of evaporator. When frost is formed, the refrigerant entering the evaporator coils does not evaporate completely and there is danger of evaporated refrigerant flooding back to the compressor, which may cause damage. Hot Water Spray: For this first close the stop valve before the evaporator. Spray the hot water from accommodation with the flexible hose on the evaporator coils until all the frost melts. Water collected in bilges is to be drained before starting the system again. Electrical Heating: Electric heating coils are installed between the evaporator coils. These coils heat the atmosphere around the evaporator and defrost it. On completion of defrosting electric coils are put-off and water is drained from the compartment before starting the system again. Refrigerant Hot Gas: In this method refrigerant hot gas from the compressor is directly passed to the evaporator coils without passing it through the condenser and expansion valve. On completion of defrosting, gas supply is put-off and water is drained from the compartment before starting the system again.