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Hey All
It is a known fact that you cannot place a HFC refrigerant into a cfc hermetic compressor system without Crystalising the mineral oil.
So why is it that the chemical composition for the R12 drop in replacement R413a is composed of 88% of R134a.
Wouldn't this cause the original mineral oil to crystalise?
Neil
Hi Neil,
I don't know the technical answer to your'e question but all i can say is it works !!!.
In fact i have seen a lot of old r12 freezers running ok on R134a. At the end of the day these units are that old that even if you only get 2 years work out of them before the compressor pops and the leak is easy to do then why not try it.
Have to admit though nine times out of ten i would condemn the whole thing if it is on r12 and it's not a quick repair. that would rise to 10/10 if the compressor needed replacement
Regards
Raymond
Maybe the R600a that helps to carry the oil.
Just something i read over at Xtremesystems, that HCs helps carry oil or something like that :).
you should be able to convert r12 to r134a it is the same as a car you need to buy a retrofit kit witch contains a can or 2 of oil propelled by r134a, a can or 3 or 4 of r134a and the connector nipples to change the 1/4 nipples to the quick connect like used in air tools.
Not heard about the oil crystalising.
The mineral oil doesn't chemically bond with R134a. It will get washed along with liquid refrigerant into the evaporator, then when the gas evaporates it will log there. That's why drop in's have a HC (typically about 2%) which bring the oil back.
Cheers,
Andy.
There's your problem.Quote:
Originally Posted by neil sailes
Believing old wive's tales like that.
It is about 2 things.
Miscibility of oil in refrigerant. As has already been mentioned, mineral oil isn't miscible in HFC refrigerants. In a properly designed piping system, this might now be a problem, but if the piping isn't exactly right for oil return, you are going to know it.
The other problem with older systems is wax. Mineral oil tends to hold wax better. Being a synthetic, POE oil will not hold the wax.
This is probably where the crystallization idea started from.
With a newer system and more highly refined mineral oils, I doubt that you would see a wax problem at all.
I lot of what happens depends on the system. In small close coupled systems, the flow of refrigerant may have enough "brute force" to physically move the oil around the system, even if it is a non-miscible pair like 134a/MO. For other systems, with more difficult oil return, it is probably best to select a product that has a small amount of hydrocarbon in it to enable the mineral oil to move out of the cold evaporator. Otherwise a change of oil will be needed to allow adequate oil return.
Even with that "small amount" of HC, which normally is around a 3% of the volume, the oil return is not ensured. It will depend on the design of the system, in many cases, you don't have any oil return, and here some chaps have argued that already.
Best is to change the MO directly, either rinsing or flushing(recirculating a miscible refrigerant with MO, R22, i.e.)
Regards,
Nando.
I have been using 401a or mp39 as a drop in replacement for r12 for years never had one problem
Quote:
Originally Posted by huskerdu
Those gases used to replace R12 were really "drop in" products, as they were miscible with MO. The problem comes with the new "drop ins" which are not really "that drop in", as they are almost HFC's. So, an oil change should be recomended in many cases.
Regards,
Nando.
MP39 and other service blend refrigerants (HP80, 81) all contained a signifcant percentage of R-22. Due to the good solubility of 22 in MO or AB type lubricants, oil return was not so much of a concern. But as these R22 products are also being phased out, switching to HFC and/or HFC/HC blends one needs to closely look at individual systems to determine best course of action for oil changes.