Training FAQ
 

1.ODS phase-out on the global scale

Q1 Will larger systems continue to run on CFC?

All new machines, large or small will be filled with CFC substitutes only with effect from 01/01/2003. R12 or CFCs will not be used on any appliance or machine manufactured after 01/01/2003.

Machines existing before this date and fitted with CFCs can continue to run on CFCs. However the problem that these units will face in due course will be the shortage and non availability of CFCs and therefore they will have either to retrofit the appliances/machines to CFC substitutes or recover and recycle the CFC used so that it is available whenever they need CFCs. Many large users might resort to banking of CFCs for future use.

Q2 Are there any alternative to HC and R-134a?

Blends using R22, HFC152a & HCFC124 were used as substitutes for R12 (particularly for Retrofitting), the advantage being that instead of POE oils, a synthetic oil like Alkyl Benzene which is less hygroscopic was used, in the United States. However as these blends have also to be imported into India , it has been more or less established that HFC134a or HC blends would be the only replacements for R12.

3. RAC technical issues related to CFC phase out

Q1 What is the difference between Molecular sieve and Silica gel drier?

The non crystalline silica gel does not have as much water adsorbing capability as the Molecular sieve at the temperatures encountered in refrigeration. Also that Silica gel adsorbs some of the lubricating oil and refrigerant also in addition to the water molecules because of larger pore sizes as compared to Molecular sieve which have smaller pores and adsorb only water molecules. Further as compared to molecular sieves, silica gel has less strength and can shatter when contacted by liquid water and when subjected to repeated freeze thaw cycles. This leads to capillary chokes. Apart from the above reasons, the weight of silica gel to be used to reduce a R12 system's moisture level will have to be about over 5 to 6 times the weight of the molecular sieve needed for the same purpose.

Q2 Why silica gel is not recommended for R134a?

In fact silica gel is not recommended even for R12 on account of the reasons mentioned above. In the early days before molecular sieves were developed, silica gel was used and continues to be used in servicing but not by any reputed Appliance OEM even for R12.

Q3 What is the specification of XH-7/XH-9 other than that of molecular sieve?

XH7 & XH9 indicate the type of molecular sieves made by UOP (US manufacturer) that use the brand name MOLSIV and the desiccants are designated by them as MOLSIV 4A- XH 7, MOLSIV 4A- XH9, MOLSIV 4A- XH5, MOLSIV 4A-XH6. The prefix 4A is used by most molecular sieve manufacturers and indicates that the size of the pores in the molecular sieve is 4 Angstrom or 0.4 nm (nano meters). The suffix XH 5 etc are the designations given by UOP to the molecular sieves developed by them. The higher the numbers following XH indicates a newer development and is also indicative of higher hydrated attrition strength (particularly XH7 & XH9) needed for 134a.
Other specifications applicable to most desiccants also apply to molecular sieves; these being, Water capacity, Bead size (usually 1/16" for mol sieves and 1/8" for activated alumina and silica gel), crush strength, attrition strength both dry and hydrated.

Q4 If both XH7 & XH9 are suitable for 134a what is the difference between the two?

XH7 was first developed for 134a for Auto AC systems after it was found that the existing XH5 used in R12 systems reacted chemically with 134a, apart from lower hydrated attrition strength. It was found to be ok for both auto AC and stationary systems as well as with R12. However it is not recommended for R22 systems. XH9 was subsequently developed as a more versatile product suitable for all 134a, R12, R22, HFCs 125,143a & 152a.

Q5 What is the specification of XH5 used in R12 & HC systems?

Specifications are covered under Question-3 above. XH5 can be used in R12 & HC systems. However it is not recommended for R22. Infact for R22, both XH5 & XH7 are unsuitable and either 4A XH6 or 4A XH9 are to be used.

Q6 What is the structural difference in the filter drier used in CFC and HFC appliance?

XH5 can be used for R12 & HC systems; XH7 and XH9 are used for R134a systems. These are molecular sieves, higher the number following XH indicates a newer development and is also indicative of higher hydrated attrition strength. For a given quantity of molecular sieve XH7 or XH9 will have more surface area than XH5 to adsorb water.

Q7 Can we use drier with silica gel as desiccant for R134a Systems?

Because of absorption capacity of silica gel, acid formation takes place. The POE oil used in R134a systems is sensitive to this. Hence it is not recommended to use silica gel in R134a systems.

Q8 Can we use XH-7 on XH-9 dehydrator for HC blend?

Use of XH7 or XH9 for HCs would be OK. However XH5 which is used for R12 is good enough for HCs. XH7 was specially developed for 134a as XH5 was found to be:
a) Chemically incompatible with 134a
b) Did not have adequate moisture absorption capacity
c) Did not have adequate bead crush strength
d) Inadequate resistance to attrition caused due to refrigerant flow.

XH9 was developed for use with HFC152a and its blends but was also found suitable for a variety of refrigerants like R22, R134a etc.

Both XH7 & XH9 can be used with R12 and HCs also but it is clearly a case of “Overkill” since XH5 that is used with R12 can be very well used.

b. Hydrocarbon Refrigerants

Q1 Why CFC domestic refrigerators of 375 grams charge and above of R12 should not be retrofitted with HC blends?

The LFL is 35grams/cu m for HC refrigerant. Assuming a factor of safety of 4, this figure is further reduced to 8 grams/cu m of given space. In a typical room in an Indian home, of 3 X 3 X 2.5 m as shown in the example in the manual, the maximum permissible HC present can be 8 X 3 X 3 X 2.5 = 180 grams of HCs. A refrigerant charge of about 450 grams R12 translates into 180 grams of equivalent HC blend charge. However this will hold good if the entire HC charge of 180 grams were to be uniformly dispersed in the room. This never happens in practice as HC is heavier and stratifies in the room, leading to the possibility of reaching the LFL level at some strata. To be still safer therefore and considering the possibility of even smaller rooms, the upper limit has been kept at 375 grams of CFC for Domestic refrigerators.

Q2 Can we use HC blend in Air conditioners of capacity less than I TR capacity?

Theoretically, using a HC blend is like using R12 in an AC. Apart from the fact that the capacity will reduce by over 40%, if the system to be retrofitted is a R22 system, the electricals in the system will have to be made exproof or sealed, as in the case of refrigerators and the capillary will also have to be changed. The main problem again will be the charge which will exceed the limit mentioned in the previous question. Even a 0.75 TR AC has a charge of about 600 to 700 grams R22 and the equivalent HC charge will be in excess of the limits mentioned in the previous question. It is therefore not recommended.

Q3 If HC blend is overcharged how to correct it to the actual charge?

HC blend has to be accurately charged using weigh scales. In the event of an accidental overcharge, it is very difficult to bring the charge back to the desired figure by purging and checking the back pressure. Further, purging of HC is dangerous and not desirable. The performance of a system using HCs is highly sensitive to the charge and therefore the only other alternative is to vent the entire charge to the outside (well ventilated place) using the recommended method and recharging the unit again accurately.

Q4 In case of short winding in a refrigerator charged with HC, is there a danger of fire?

For any substance to catch fire we need fuel, source of ignition and oxygen. In the case of short winding in a refrigerator charged with HC, fuel and source of ignition is present but oxygen is absent, hence there is no danger of fire. It is dangerous when there is a leak in the system with a source of ignition around.

Q5 Can HC blend be replaced with CFC-12?

Yes. But when we are aware of the damages that the CFC can cause and the global community is doing so much to phase out CFC, is it right on our part to re-convert an eco- friendly refrigerator to something that will harm our atmosphere?

Q6 Why don’t we recover HC?

HC Blend can be recovered but need to have a separate recovery and recycling unit. Further it should be colleted in a separate recovery cylinder assigned for it also while recovering HC Blend (mixture of R290 and R600a of each 50%) in the initial we may get only one gas because of “zeotropic” nature of this Blend.

HC Blend doesn’t have ODP and negligible GWP, hence letting the gas into open air don’t make any difference in environmental view point. All in all quantity present in domestic appliances is very low and is not economical to recover.

Q7 How do we charge HC blend by pressure method?

Without any clue, charging by reading the back pressure (suction side) must be done of course. The back pressure of R600a is much lower compared with the other gases. At 10°C R12/ R134a/ HC mix is appx. 1.2 bar g, R600a below 0 bar g (in vacuum). Thus performance must be optimised by charging.

Else charge little quantity and switch on the system and observe for formation/feel of frost in the evaporator. If not, again charge little quantity and like wise till formation of frost in the evaporator. However it is time consuming process.

Q8 For HC Blend, R 290 and R 600a mixing is locally possible?

Yes it is possible, but need to take precautions (because of flammable nature of these gases), very precise and unwavering measurements while performing the same.

If though possible, it doesn’t mean that this is legal. For cleaning and mixing of gases the enterprise doing so must have a license. Mixing directly into a refrigeration system is not practical.

Q9 Whether HC Blend can be used for retrofitting in place of R134a?

Yes, it can be used; the capillary may need some correction and electrical components will have to be changed to the non sparking type. It may be also worthwhile changing from POE oil (which is highly hygroscopic and creates problems in 134a systems) to Mineral oil. This would mean removing the oil from the compressor and flushing the system of all POE oil and then refilling with Mineral oil. There is a possibility that the Motor of the compressor may get overloaded with retrofit (just as it does when R12 is filled in a 134a system) and will depend on the rating of the original motor.

Q10 If HC blend is charged excess, can we remove it in liquid stage from double mouth drier?

HC Blends are Zeotropes and have a fairly pronounced temperature glide. That is why the blend should be charged as a liquid. For the same reason, any leak in the system, particularly at a site where the gas is part liquid and part vapour (like the evaporator) can cause the gas left inside the system to change its composition. Now, the situation of charging excess gas will arise only if the gas has not been charged by weight or if gas higher in weight than the recommended quantity has been charged through pure oversight or negligence. Whilst the former method of charging by traditional methods other than weight is not recommended for HCs (because of the very low weight of the charge and the extent to which performance gets affected even due to a small deviation in the recommended charge) the latter cannot be condoned and therefore on both these grounds this question itself should not be encouraged or entertained.

On purely hypothetical grounds, yes, the charge weight can be reduced by withdrawing the gas as a liquid from those sites where the gas exists as a liquid. But the question here is how will one know how much weight has been pulled out and how much is left behind in the system? One partial answer to this is that the gas that has been withdrawn can be recovered into a pre weighed empty cylinder. But this too will not enable us to know how much weight of the charge is left behind in the system and could result in an under or overcharge resulting in poor performance. It can therefore be seen that this question cannot be entertained on any grounds as analysed above and can be perceived as one having the same mindset and approach that he still has for R12.

Q11 HC blend– What is the flammability?

To get ignited, the concentration of HC blend in air has to be between the Lower and Upper flammability level. For HC the lower flammability level is 2% and Upper flammability level is 10%. Both the values are on Volume basis.

App. gram value of HC for a 2% concentration by volume is 40 gram of HC per m3 of air, for a 10% concentration it is 200 grams per m3 of air; pressure 1 bar.

Q12 Can HC be used in deep freezers?

Yes it can be used however for safety reasons it is not advisable to use it for appliances where the HC charge will be more than 150 grams.

Q13 By charging refrigerant as liquid will the compressor be damaged?

Yes! No liquid may enter the compressor on the suction side!
There are two things which assist the evaporation of the liquid into a vapour, these being the Polyamide Capillary hose (or even Copper capillary used by Godrej) provided by Refco between the HC can and the manifold and secondly the presence of deep vacuum in the system that convert the liquid into a vapour. Apart from this the throttling at the valves for controlled entry of the refrigerant into the system also assists this.

The danger of liquid entering the compressor is the possibility of the valve reeds breaking or the connecting rod getting bent or even damage to the valve plate.

Q14 If compressor winding in a HC blend charged system is short will there is an explosion in the compressor?

Three components are needed simultaneously for causing fire i.e. Oxygen, an ignition source with sufficient energy and right concentration of HC gas. Since there would not be any chances for air to intrude into compressor, chances of fire are unlikely.

Q15 With HC if there is a system leak will there be fire?

If a leak takes place in the evaporator of a refrigerator then it can be seen that there is every possibility of a hazard as the three essentials for a fire i.e. gas (due to leakage), air (exists inside the refrigerator) and a spark (from thermostat contacts, floor switch and lamp holder) are all available. That is why these components are replaced by sealed or non explosive components. Like wise leaks near the compressor can create an explosive situation if there are sparking components like relays and overloads which have to be replaced by PTCs and sealed OLPs.

Q16 Does frostbite happens with HC refrigerant like R12 and R22 refrigerants?

The gases which are being used as refrigerants have a very low boiling point will cause frostbite when fallen on skin and the same case with HC refrigerant as well.

Q17 Why do we charge HC blend slowly?

Since the refrigerant is charged into the process tube of the compressor, any liquid present must be evaporated before it enters the compressor, otherwise it may lead to compressor failure. Hence it is advised to charge the HC blend slowly.

Q18 Is it possible to replace R-600a compressor with R-134a/HC compressor?

It is possible to replace but has to take care of capillary, filter driers, quantity of charge required, Oil to be changed (but generally comes with the compressor) etc.

c.HFC Refrigerants

Q1 Can we charge R12 in a 134a system? What will be the consequence?

Apart from violating the Ozone Rules, the following technical problems can also arise:
a) Cross contamination of R12 and 134a can lead to an unpredictable performance.
b) Capillary for 134a systems is usually about 40% to 60% longer than those for R12 for the same bore of capillary. This will affect performance.
c) Compressor motor can get overloaded and burn out.

Q2 Can we charge 134a (being a single fluid) observing the back pressure?

Theoretically yes, if the back pressures that are to be obtained for various evaporator temperatures at different ambient temperatures, are available from the OEM. Here again, when charging is done in the field, ambient temperatures are never constant (unlike the temperature controlled test room of an OEM) and a certain inaccuracy is inherent. Considering however, that in India, such information from OEMs is not available and also considering the inherent inaccuracy in the method, this is not recommended and the best practice is to use a charging still or even better a weigh scale. Please remember that compared to R12, 134a is more charge sensitive.

Q3 How to check the pumping of a 134a Compressor?

The best thing is to enquire the compressor manufacturer or OEM the way this can be tested. In India, KCL, Tecumseh and Godrej have their own recommendations. One universal method that can be adopted, subject to Compressor manufacturers agreeing, is to use a Compressor tester, which comprises of a Receiver like vessel with a relief valve and pressure gauge at one end and a hose with a quick coupler at the other end. The compressor has to be connected to Nitrogen through a syringe to avoid moisture. The syringe needle has to penetrate the rubber plug on the suction tube stub. The discharge tube stub is then connected to the quick coupler mentioned above. Nitrogen pressure should not exceed 0.5 to 1 barg. After all the connections are made the compressor has to build its own pressure of 16 bar. After the compressor is switched off, a pressure of 12 to 14 bar must be held for 60 seconds. The loss of pressure should not exceed 2 bar in 60 seconds.

Q4 Why is the Capillary length of R134a more than one using R12?

Capillary length for a particular bore is dependent on the condensing and evaporating pressures and the mass flow and the transportation properties of the refrigerants. In this case the condensing pressure for 134a is about 10 to 15% higher than that for R12 whilst the evaporating pressures are lower than that for R12. The mass flow of 134a is lower than that for R12 while properties like viscosity etc are different. All these reasons lead to the capillary length for 134a being higher than that for R12.

Q5 What is the viscosity of POE oil?

POE oils have viscosities close to that of mineral oils that they have replaced for HFC refrigerants. They are graded according to ISO standards Viscosity grades. For refrigerators the Viscosity for R12 is VG 32 which is similar for POEs. However, POEs with a little lower viscosity VG22 is also used. Ultimately, you should use the oil recommended by the Compressor manufacturer and not any other oil as compressor manufacturers have done a lot of studies and application engineering work jointly with the oil manufacturers in arriving at the grade of oil most suitable for HFC refrigerants for their compressors.

Q6 How long can POE oil be kept exposed during servicing?

As short a time as possible, not exceeding 5 minutes preferably. A method that could be tried is to use a hand pump that has an adaptor that fits the can of the oil and from which a measured quantity of oil can be pumped into the compressor. This will prevent exposure of the oil to the atmosphere.

Q7 What should be the charge weight of 134a against a specific charge weight of R12?

It should be approx 90% of the charge weight of R12.

Q8 If the evaporator is found leaking in a 134a system, how do we service it?

If the evaporator of a refrigerator is damaged and if it an aluminum evaporator , it would be better to replace the evaporator and also the compressor, as a low side leak would have definitely allowed a lot of outside air and humidity to enter the system and contaminate it.

Q9 During HFC charging we are using weight as the measure for charging and perfectly agree that this is better than using suction pressure or temperature as the basis for charging. However, if the discharge pressure (pumping) of the compressor is less that adequate, can we still get the appropriate refrigeration effect by using weight as charging measure?

Charging by weight is the correct procedure as long as the weight is the one that is recommended by the appliance manufacturer. The manufacturer arrived at the correct weight by carefully optimising the charge to the appliance’s components. You just can’t put any approximate weight that you like. If after charging according to the manufacturer’s specifications (normally the weight is recorded on the nameplate of the appliance), it is found that the discharge pressure is little lower than what you normally get by other approximate methods and if you still get the expected cooling of the appliance, then there is nothing wrong. In case no proper cooling takes place, the discharge pressure is considerable lower than expected, the other components in the system are ok, then the compressor must be repaired or replaced. There is no cure to it with playing of the charge. This is of course subject to the condition that the technician has kept the size of evaporator, condenser and capillary and also compressor identical to the one supplied by the manufacturer.

Q10 Can anti-choke be used in systems with HFC-134a?

No. The POE – 134a combination is not tolerant to contaminants and there will be sludge formation in the capillary and other parts of the system leading to system failure.

Q11 When 134a is charged in to a system where mineral oil is used as compressor lubricant, it works. How come?

As long as there is enough lubricating oil in the compressor it will keep working. Since mineral oil is not miscible with 134a refrigerant, any oil that will get pumped in to the evaporator cannot get back to the compressor and will lead to compressor failure in the long run.

Q12 Under what circumstances can a flammable mixture of HFC134a could get formed in a workshop?

The condition at which HFC 134a could become flammable is as follows:
60% HFC in the air at 0.4 bar gauge pressure and at a temperature of 177° C. The chance for all these parameters to match at a time is unlikely. This can probably happen if there is a fire due to other reasons in a workshop (temperatures can reach or exceed 177°C) and 134a gas has leaked extensively in the workshop. At ambient temperatures, all concentrations of 134a in air are non-flammable at pressures below 15psig i.e. 2 Barg, according to DuPont’s literature on 134a.

Q13 What is the chemical name for HFC 134a?

Chemical name: 1,1,1,2-tetrafluoroethane
Chemical formula: CH2FCF3

Q14 How is oil affected by moisture?

Oil, particularly POE oils used with HFC refrigerants is highly hygroscopic and dissolves a large amount of water. This water reacts with the POE oil to form Polyol and Acid which are the original building blocks for making POE oil. The acid in turn starts corrosion of the system components. The moisture also forms sludge with the oil which causes partial/full choking of the capillary.

Q15 If there are leaks in R-134a – refrigeration system does the compressor need to be replaced?

The practice followed by Whirlpool, is to replace the compressor itself if it happens to be a leak on the low side. However if it is a leak elsewhere, the compressor is not replaced. This makes sense as a leak on the low side can draw in outside humid air in big quantities and contaminate the POE oil badly.

Q16 Will R-134a be replaced eventually?

As far as the Montreal Protocol goes 134a has zero ODP and therefore well accepted as a CFC replacement and hence no question of a phase out. As far as the Kyoto Protocol (KP) goes, HFCs is one of the basket of six gases identified for controlled emission. The KP also does not talk of a phase out but of emission control because of the relatively high GWP of HFCs.. individual countries (particularly in Europe) have taken their own decisions to minimise the use of HFCs to reduce the risk of Global warming. The US (which has still not ratified the KP) is still betting on HFCs by tightening the emissions and improving the energy efficiency of HFC using machines. As of now, therefore, with the world’s big power blocs thinking in opposite directions, there does not seem to be any immediate threat of a phase out of HFCs.

Q17 How to recharge oil in R-134a system?

The oil should not be exposed to the atmosphere and the best way of charging oil is by fitting a hand operated pump directly on the mouth of the oil can and connecting its outlet through a hose to the compressor’s process tube whereby everything is a closed circuit without exposure to the atmosphere. Alternatively, after evacuation and leak testing, the oil from the sealed tin can be drawn in by the vacuum into the compressor.

Q18 Skin condenser – how to add 10% to it?

As we recommend while retrofitting with 134a a bigger condenser is required to keep the discharge pressure down. At the same time we also say that we do not recommend a retrofit with 134a.

Q19 Can we retrofit a CFC appliance with R-134a by changing the oil alone?

We have to ensure that the percentage of mineral oil left behind should be only 1% (at least 5%) by weight. This is done by emptying the mineral oil from the compressor, filling POE oil and then running the system on R12 for at least 48 hours. After that the percentage of mineral oil is measured using a Refractometer and if it is found higher than 5% the process is repeated again and again till the percentage is brought down to at least 5% or better still 1%. It has been found that it is necessary to run the system at least three times like this i.e. totally for 6 to 7 days to reduce the residual mineral oil to this level. All this is time consuming, labour intensive and also does not guarantee safe working with 134a later. So, even small hermetic appliances were never retrofitted with 134a. They were either replaced or continued to operate with CFCs on recovered CFCs.

Q20 How to test the pumping effectiveness of R-134a compressor?

Connect the Nitrogen cylinder to the process tube of hermetic compressor using a two stage pressure regulator. The discharge side of the compressor to be connected to the receiver or a condenser coil having appropriate capacity. The other end of the receiver/condenser coil to a pressure gauge which can read 0 to 300 PSIG.

Check for leaks at all joints using soap solution and then supply Nitrogen gas at a constant pressure of 20 PSIG in the process tube of the compressor. Start the compressor and run for few seconds to build a head pressure of value as specified in the table below. On attaining the specified discharge pressure stop the compressor and check for drop in pressure for a period of one minute and verify whether it falls with in the specified limit in the table. If the pressure drop exceeds the specified limit, the compressor has a pumping defect, otherwise the compressor is OK.

Group Leak rate per MIN (PSIG) Head pressure (PSIG)
AE 30 125
AJ-CAJ 30 125
AH/CR 6 40/45 150
AG 60 200

Q21 How a chocked R-134a system will be checked through suction side?

A partial chock will result in a very low suction pressure (even a deep vacuum) and higher than normal discharge pressure.

Q22 Is it required to change expansion valve and other components for CFC 12 system while retrofit with R-134a?

In thermal evacuation systems, the expansion valve has to be changed or reset to adjust to the higher pressure ratio. Other components like filter drier, compressor oil, capillary length etc also have to be changed.

Q23 Capillary size design of R-134a system while retrofitting R12 system?

The capillary tube is usually 10-20 % longer for R-134a systems.

d. Recovery & Recycling

Q1 Can we use a common Recovery machine for both CFC & HFC systems?

A common recovery machine can be used, if every time, a change in refrigerant handling is encountered, the machine is evacuated and all traces of the earlier handled refrigerant is removed. A vacuum of at least 1000 microns is needed for this. However, as such disciplined procedures are seldom practiced in the field, it is safer to use separate Recovery machines for each of the refrigerants. Separate Recovery cylinders are to be used for each refrigerant. It should be remembered that R12 & 134a form a high pressure azeotrope in all proportions and a contamination exceeding 2 to 3% is bad.

Q2 Any simple test to identify the acidity in lubricants?

The simplest test is to use a litmus paper that turns from blue to red. This only tells you of the presence of acid but not whether it is at an acceptable level or not. A better test is the use of 'Acidity Test Kits' which are not made in India but available through Total Line of Carrier Aircon. This is made by Sporlan of the USA and comprises of 3 bottles: A small bottle with a colourless liquid for Mineral oils, another small bottle with a colourless liquid for POE oils and one large bottle with a orange coloured solution. The procedure is that the colourless liquid from one of the small bottles (depending on which oil is being tested) is poured into the big bottle containing the orange coloured solution. This will turn the colour orange to Purple. Add the sample oil to the large bottle and shake 15 times. Observe the colour after this:
• If it is still purple, it is ok and not acidic.
• If the colour turns Orange, it is somewhat acidic and not very satisfactory. For POE, it indicates 0.17 to 0.23 TAN.
• If the colour turns yellow, it is unsatisfactory and to be rejected. For POE, it means a TAN>0.23

For low temperature hermetic applications like refrigerators TAN lower than 0.17 is preferable. However refrigerant (oil) that indicates Orange colour can be used for Auto AC. TAN stands for 'Total Acid Number' and indicates the weight of KOH (Potassium Hydroxide) in mg required to neutralise a gram of liquid containing the acid.

The price of such a kit (for a one time use) is approx Rs 500.

Q3 What could be done with the recovered and stored CFC?

This is a difficult to answer at this stage as there are no rules or regulations existing in the country. Yes recovered refrigerant can be reused, preferably in the same system from which it was recovered as long there is no Motor burnout. However if facilities are available to do a quick moisture or acid test of the refrigerant, the refrigerant can be used after recycling depending on the results of the test. Even here, it is better if the recovered refrigerant is used in the same system from which it was recovered, in the absence of any rules or regulations. The problem is the non availability and high costs of recycling machines. However NCCoPP is working towards formulating country guidelines for Recovery and recycling, proposals are under way.

Q4 : What to do with the recovered refrigerant? (Category 4)

Recovered refrigerant when not contaminated or only marginal can be used in the system again after repair. (With a compressor burn out, refrigerants are heavily contaminated.) Of course, best is to recycle all refrigerant before reuse. But this is an economic question as multi pass recycling machines are not cheap and thus only economical if sufficient refrigerant can be recycled over time. For this a group of technicians from the same locality could join together and purchase one machine and start recycling. Refrigerant recycling and reuse can only be done if refrigerants are not mixed! Hence keep separate cylinders for each and every recovered refrigerant. In the future the Govt. might start some recycling centres at some selected cities or towns and technicians will be able to make use of the same.

Q5 How will have to keep recovered refrigerant?

CFCs and HFCs are recovered in a recovery cylinder using a recovery machine. It is also recommended that the cylinder be labelled with the following information:
• Name of the refrigerant stored inside
• Weight
For further details please refer HIDECOR MSE Handout.

e. Servicing Practices

Q1 Using Nitrogen at 10bar makes the oil in the condenser and evaporator to come out?

Flushing need be done at 5 bar only.

Q2 How do you read microns in the Refco Vacuum Gauge?

The Refco Vacuum gauge is calibrated in Milli bars or mb and the smallest or lowest reading that can be read is 10 mille bars which is about 7600 microns. For reading in microns below this, it is necessary to use a gauge that can read lower than this i.e. Pirani or Thermo couple gauges.

Q3 Trichloroethylene also contains Chlorine and is recommended for cleaning. Will it not also contribute to the Ozone layer damage?

The chlorine in Trichloroethylene does not rise to the stratosphere and contribute to ozone damage. It is not as stable as CFCs and the chlorine in it gets separated and lost in the lower atmosphere. It is therefore not listed amongst the ODS in the Montreal Protocol that needs to be phased out.

Q4 What is the correct measure of Vacuum, is it the level of vacuum or the time the Vacuum pump is kept running?

The level of Vacuum, as measured in microns of Hg in a Vacuum gauge (that is of the Pirani or Thermocouple type) is the right measure of Vacuum. The recommended is at least 200 microns (100 microns desirable) Hg for 134a and 500 microns Hg at least for R12. After achieving this level of Vacuum, the Vacuum pump should be isolated with the valve and stopped and the Vacuum holding capacity of the system should be checked. If the pressure rises slowly and then stabilises at a higher level of microns, it means that there is some moisture still remaining and the Vacuum pump should be restarted and reconnected and run again for about 10 minutes and the rise in pressure checked again and this process should be repeated till the rise in pressure is as low as possible, suggesting that almost all the water vapour has been removed. After this has been achieved, the Vacuum pump should be run for another 5 to 10 minutes before proceeding to the next step of charging refrigerant.

Q5 Evacuation needed for HFC is to be as low as 100 Microns. Is such low levels needed for HCs also?

HCs can be evacuated to the same levels as CFCs i.e. at least 500 Microns. Moisture can be as detrimental in an HC system as in a R12 system. Further the solubility of HCs in oil as well as the solubility of moisture in HCs is higher than in the case of CFCs. Therefore it is better to evacuate HC systems to at least 500 microns and for HFC system is at least 200 microns.

Q6 The ideal clearances between tubes, for brazing, for good capillary action has been mentioned as 0.05mm to 0.200mm. What should be the depth of insertion?

The depth of insertion gets automatically determined when a correct swaging tool is used to swage the end of a tube which is to be brazed to another of the same size. It is usually kept equivalent to the OD of the tube. It is possible to also braze a smaller tube of 1/4" to a bigger tube of 3/8" tube without any swaging. However the clearance between the tubes becomes much higher than the permissible 0.200 mm and here the insertion has to be longer (about 0.75 to 1 inch) and a brazing rod with 15% Ag and 5% P has to be used even for Cu to Cu brazing. However when brazing a 3/16" Cu tube to a 1/4" Cu tube it will be necessary to swage the end of the 1/4" tube, as otherwise, the clearance between the tubes becomes too small (0.025mm).

Q7 What is the purpose of using flux? What is it made of?

Oxidised metal surfaces cannot be brazed and thus need cleaning beforehand. This cleaning action is performed by the Flux. Flux reacts chemically with the metal oxides and dissolves them and prevents oxides from reforming. Flux becomes fluid at brazing temperatures and adheres to the base metal. Flux is then displaced by the molten filler in the brazing process. Flux is required when brazing ferrous metals with filler rods not containing Phosphorous.
Fluxes are formulated from many chemicals e.g. acid, Borates, Fluorides, Fluoborates, Deoxidizes, water & wetting agents and are available in the form of powder, paste and liquid.

Q8 What is the minimum required level of Ag content in Brazing rods?

Cu to Cu brazing does not need Ag though the presence of 2% Ag helps a lot. However 15% Ag rods is recommended even for Cu to Cu brazing where the clearances between the tubes is high , as explained under Question no 6 above. For Cu to steel or brass, at least 35% Ag is needed, Infact, 45% Ag would be the best.

Q9 Whether it was possible to use Dry Ice (solid CO2) in a cold trap to eliminate the moisture that was being removed from the system?

Yes, this can be done, as it will help in reducing the load on the Vacuum Pump. An article on how to use the Cold trap with Dry Ice is attached.

Q10 Availability of portable Nitrogen and Oxygen cylinders?

At present only Godrej have succeeded in developing sources for small Nitrogen and Oxygen cylinders in Mumbai. It has to be seen whether the suppliers have an all India (or at least in HIDECOR focus areas) distribution network and a study will have to be done on this.

Q11 Cost of sealed electrical components when retrofitting to HCs?

Sealed door switch - Rs. 07.25/-
Sealed lamp holder – Rs. 10.60/-
Sealed OLP for HC compressor – Rs. 32.00/-
PTCR for HC compressor – Rs. 35.00/-
Sealed thermostat – Rs. 95.00/-
Note that all the mentioned costs may vary from place to place

Q12 How do you know what gas is inside a system if the label on the refrigerator is missing?

Keep the refrigerator in a well-ventilated area. Connect a piercing valve to the process tube of the refrigerator compressor and at the outlet of the piercing valve connect a long capillary. Open the piercing valve slowly and allow small quantity of refrigerant to come out on to a match/ cigarette lighter flame.

R134a when burned, the colour of the flame does not change.

R12 when burned, the outer lining of the flame gets a greenish tint.

HC (R290/R600a) burns by itself.

HC (R600a) burns by itself. But pressure in the systems is much lower (at 30 °C appx. 2.5 bar gage) than with the other gases (at 30 °C appx. 6.5 bar gage). Hence a pressure test will indicate immediately whether it is R600a or another gas. But no R600a is on the market in India at present.

Such tests should be done very carefully trough a capillary and in open air. Burning of R134a and R12 produce toxic gases. HC is flammable.
Question is harder to answer when no gas is in the system anymore. The label on the compressor might tell, sometimes this is also engraved in housing. The age of a refrigerator is also a telltale. Also, the name of the fridge may tell. If the name indicates environmental friendly then it is R134a or HC. There might be an indication of the manufacturer and type of the fridge and the easiest way to find out is thus to call the service line of the manufacturer. If the fridge is so old that they donot know anymore, then it is R12 anyway. All fridges before 1996 are most probably R12. Maybe there is a manual still with the owner? The filter dryer used might also indicate (type XH7 & XH9 used for R134a, type XH5 used for R12 & HC systems and XH6 or XH9 used for R22)

Charging: Without any clue, charging by reading the back pressure (suction side) must be done of course. The backpressure of R600a is much lower compared with the other gases. At -10 °C R12/ R134a/ HC mix is appx. 1.2 bar g, R600a below 0 bar g (in vacuum). Thus performance must be optimised by charging.

Q13 Why do compressors pump oil? / How does the system get choked with oil?

In any system when a compressor is working, certain amount of lubricating oil is always pumped out of the compressor along with the refrigerant, however this returns to the compressor along with the refrigerant because of its miscibility with the refrigerant. In the evaporator, oil viscosity is high due to the low temperatures there. If the refrigerant mass flow gets reduced due to partial capillary choke or partial gas leak the refrigerant velocity will not be adequate to carry the oil with it back to the compressor. This results in system oil choke.

Q14 What is the harm in using locally re-winded compressor with R 134a?

It is not recommended mainly because the insulating material used by the local re-winders may not be compatible with R134a and POE oil used in R134a system.

Q15 How system heating is affected for getting vacuum?

Firstly heating the system is not recommended. This may damage electrical components, quality/sensitivity of oil may get affected and later this may lead to system failure.

Q16 What is the effect of using anti-moist in a system?

Anti-moist is a contaminant. The POE – 134a combination is not tolerant to contaminants and there will be sludge formation in the capillary and other parts of the system leading to system failure. The same effect could be expected in other refrigeration systems; hence it is not advisable to use anti-moist.

Q17 How can oil be identified in a compressor with unknown refrigerant?

Without tests to be done in a laboratory this is difficult. Hence for a technician first find out what has was/is in the system. This issue is covered earlier on. If it is observed to be HFC refrigerant for sure the oil in the compressor must be POE oil, else if it is CFC then the oil should be mineral oil. Apart from the above if it is HC Blend then the oil could be either POE or mineral oil, but most likely the later.

Q18 Importance of vacuum in microns

Micron is the smallest unit for pressure measurement. For example 1 mm of Hg is equal to 1000 microns (1000 times smaller) , while evacuating the domestic refrigeration system pressure may come down to around 500 microns Hg. Hence for accurate measurement it is necessary to measure the pressure (vacuum) in microns.


Q19 Why oil is not coming out of compressor during deep vacuum?

The compressor oil has certain density and boiling point. The vacuum levels (down to 200 microns) reached normally is well above the vapour pressure of oil in the compressor. Hence oil will not evaporate. Also the refrigerant In and Outlet of compressor side are well above the oil level- hence there is no chance/possibility of sucking out the oil from compressor.

Q20 Why dry nitrogen should be used?

Nitrogen is an inert gas and therefore will not react with the compressor oil as Oxygen (which is present in air) would. The dry Nitrogen would have a purity of 99.997% and a dew point of at least -40°C. Therefore the Compressor oil is unaffected and the moisture present in the system will get absorbed by the dry Nitrogen.

Q21 Can halide torch be used to check leaks of HC and HFC?

The answer is NO.
a) HFC refrigerants decompose to form toxic products when heated.
b) As HC gases are flammable, Halide torches are not recommended for leak detection. Since the gas in the system is not under safety conditions/a controlled burning.

Q22 What are the standing pressures of HFC 134a and HC Blend?

At 30 °C
HFC 134a: 98.26 psig
HC blend: 82.37 psig

Q23 Do the PTC replay work on all capacity compressors?

HIDECOR recommends PTCs in place of relays to prevent sparking when using HCs. PTC relay does work with all capacity compressors and is recommended for systems using HC Blend. Larger capacity compressors (which use more than 150g of HC Blend in domestic appliances, the same for 250 g in commercial appliances) are not recommended for using HC Blend and the same valid for PTC relay.

Positive Temperature Coefficient (PTC) relays are solid state devices which are to be used in systems handling flammable refrigerants like HC blends. This option will make the compressor safe to work with HC refrigerant.

Q24 Chlorine – what is the atomic weight?

The Atomic weight of chlorine is 35.5.

Q25 Bar-kg conversion – pressure?

1 bar = 1.0197 kg / sq.cm.

Q26 Why use 2% silver rod when brazing?

The addition of Silver firstly reduces the temperature at which the alloy starts melting. The Solidus will be at 643°C against 710°C where there is no Silver at all. This means less heat and therefore less heating of the system components. Secondly the melting range increases from 643°C to 788°C as against 710°C to 794°C where there is no Silver.

The advantage here is that the flow of the melting alloy is slower than what it is when there is no Silver. This helps in filling gaps by working on the molten alloy than depending purely on capillary action. This helps when soft annealed copper tubes are used as in the case of small appliances like refrigerators and freezers using hermetic compressors as the clearances of the brazing joints are never uniform. On the other hand, the use of Alloys without Silver results in a fast flow of the molten alloy over a narrower temperature range and the filling of the joints is dependent entirely on capillary action for which the clearances have to be correct and uniform. Therefore a better joint is possible with 2% Silver rods. As the silver content increases and reaches 15%, the melting range increases and the flow rate becomes even slower and this would be good for filling uneven clearances and creating fillets. All what has been stated above is for copper to copper brazing and all the alloy rods referred above contain Phosporus from 7 to 5% which acts like a flux.

Q27 What is 100% vacuum?

A perfect vacuum is a condition that does not exist. High-vacuum coating chambers pump down from an atmospheric pressure of 760 Torr to a pressure of 1 x 10-5 Torr. This means that for every 100,000,000 molecules of air in the chamber before pump down, only about 1 remains after. However for Refrigeration purposes it is normally not possible to reach a system vacuum lower than 250 microns or 0.025 mm i.e. 0.025 torr.

Q28 Will oil boil at deep vacuum?

Mineral oils boil at approximately 250 microns, after pump for days only boil out a teaspoonful or less.

Q29 Will R-134a / HC affect the material used as Evaporator i.e. Aluminium?

The material used in the manufacture of Evaporator i.e. aluminium can suit to HFCs and HCs. This situation would be critical when moisture enters in R-134a system, which results in acid formation and eventually eat away the Aluminium. Hence it is recommended to evacuate the system properly.

Critical with R-134a is acid formation if moisture enters system and acid can eat away AL then. Hence one more good reason to evacuate properly.

Q30 How to clear the brazing flux in the compressor discharge line?

Need to reopen the joint and replace with new discharge line/cut off previously brazed portion. If there is no passage block inside, then presumed to be everything is OK.

Q31 How do we differentiate between R12 and R22?

R12 gas will indicate a standing pressure of 93.93 PSI R22 gas will indicate a standing pressure of 180 PSI at 30°C in a cylinder.

Q32 Why a single stage vacuum pump is not enough to draw a vacuum of 500 microns?

Single stage vacuum pumps can’t draw low vacuum on account of inherent oil contamination and lower compression ratios.

Q33 What is the substitute gas for R22?

R417A is one of the replacement for R22 as it has zero ODP and suitable for new equipment and as a drop-in replacement for existing systems. Some other refrigerants under consideration are R-407C (drop in substitute), R410-A (changing compressor as pressures are higher) and R-290 (Pure Propane).

Source: The Comfort Environment Group Limited, Comfort Works, Newchapel Road,
Lingfield, Surrey RH7 6LE (UK).

Q34 What is PTC replay?

Positive Temperature Coefficient (PTC) relays are solid state devices which are to be used in systems handling flammable refrigerants like HC blends. This option will make the compressor safe to work with HC refrigerant.

Q35 Which chemical is to be used for cleaning?

For cleaning we can use trichloro ethylene, don’t use CTC as it is ODP substance and is controlled under Montréal protocol. However after cleaning the trichloro ethylene should be completely evaporated.

Q36 Which are the oils used in vacuum pump?

The oils with very low vapour pressure and will have no degassing effect.

3. Ozone Depletion and environmental impact

Q1 Why do Green house gases allow light (heat) rays/waves in one direction only from the earth to the sun?

The solar radiation coming from the sun and passing through the green house gases have shorter wave length whereas the thermal radiation reflected from the Earth's surface has longer wave lengths. The greenhouse gases trap the reflected radiation only.

Q2 What is the mean (average) temperature of the Earth?

The mean temperature was about 15°C. But the doubling of the CO2 levels in the atmosphere in the last 100 years is expected to raise temperatures by 1.5 to 5° C this century. This can be compared with a rise of 0.4°C in the entire 20th century. A one percent rise in surface temperatures could cause major disruptions in weather patterns, flash floods and unexpected droughts.

Q3 Why trichloroethylene does not effect the Ozone Layer?

Trichloroethylene degrade within 6-8 days is regarded as low troposphere ozone creators as well as insignificant (<0.5%) contributors to acid rain formation. The ODP (stratospheric Ozone Depletion Potential) is negligible and they are not regulated under Montreal Protocol.


 

 



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