R502 Substitutes

There are several refrigerants that have been introduced as substitutes for R502, the most popular being R404A and R507. But there are two more which deserve our consideration, as they offer some important advantages.

R408A: All else being equal, the evaporator temperature with this refrigerant won't be quite as low as R404A, but is very close, maybe within 1C.

The high side pressure, however would be about 15psi lower, which means less stress on the compressor. This is something to consider when we are using a compressor designed for lower pressure refrigerants such as R12 or R134A.

But here is the biggest advantage. It works with all oils. This might be ideal for an R12 compressor, which contains mineral oil, as changing to R404A or R507 would require the oil to be thoroughly (90%) changed to POE oil. This can be very difficult.

R402A: This refrigerant is at the other extreme of the R502 substitute group. It can yield slightly lower evaporator temperatures than R507, perhaps 1C or a little more, making it the best of the group for achieving lowest evaporator temperature.

The high side pressure, however will be about 10psi higher than R507, making it the most stressful on the compressor. This might be a problem for a compressor designed for low pressure refrigerants. But for a compressor designed for R22 or R404A it is no problem at all.

This refrigerant also works with all of the oils, but it is recommended that if the compressor contains mineral oil, part of this be replaced with alkyl benzene (AB) oil. This amounts to dumping out whatever you can and replacing with the same amount of AB oil. Much easier than the thorough replacement required for POE oil when switching to R404A or R507.

This makes it an excellent choice for R22 compressors.

Wonder..... how availability/cost would be on these.

The oil situation is a definite plus.

Thanks Gary.

R507 and 404 cost about 220 us and the pricing should stay stable.. These refrigerants are not going to be phased out. The blends using R22 are going to be phased out and in EU are no more already. The prices will go up like r12 did a few years back..R408 is already rising.

Damn, I wish I could have found 404 for that price, the local place wanted 370 so I ordered it online for 280. I should hunt around and find another local (or semi-local) place with better prices.

so , would r408a would be better then R22 if my compresor is built for r134a wich is on lower pressure..?
the oil dont matters much coz its still empty :)

what im worry about is , the guy who sold me the compresor said that "it will blow after a while from the captube pressure" should i be scard ?:P

So I assume that R408a could be used in a prommie instead of R404a, and pretty much have the same results ?

R408A requires MO or AB oil (R402A does too) which the prommie would require an oil change. R404A requires POE which is the same oil used in the prommie (since it's R134A from the factory). This makes switching to R408A (or R402A) in a prommie harder than a switch to R404A or R507 (both use POE). Of course this doesn't apply to R22 compressors or compressors that have been drained of oil. Lube Guide

I did a quick check, in the US R22, R402A, and R408A production stops in 2020 so prices will rise over time to R12 prices as chilly1 stated. Dupont phaseout dates

POE is compatible with all of these refrigerants. No oil change is needed for the prommie.

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Originally posted by Gary Lloyd
POE is compatible with all of these refrigerants. No oil change is needed for the prommie.

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That's what I read on a refrigerant site, yet a different one said otherwise....
Thanks Gary, I'll most likely be doing this 408a mod to my prommie in a month or two :D

I was thinking some of you may find the following thread interesting, as it involves oil separation problems with R408A and AB oil:

http://techmethod.com/forums/viewtopic.php?t=136

Very good oil transport properties is a plus in our applications.

This thread makes me think: ethylene (as every hydrocarbon) also has very good oil transport properties. I hope I won't get into separation problems with that.

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Very good oil transport properties is a plus in our applications.

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Yes and no. It is far better to separate the oil before it goes to the evaporator. But if it gets to the evaporator, we want it to return to the compressor.

The problem we encountered was that the oil refused to separate. Just the opposite of the usual problem, i.e. failure to return. It's a new one on me.

As it turns out, the solution was a mixture of oils to achieve the right balance of properties. Like so many things in refrigeration, it's all about balances and trade-offs.

In any case, it made for an interesting discussion. :D

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Originally posted by Gary Lloyd
[B]Yes and no. It is far better to separate the oil before it goes to the evaporator.

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It sure is, but I won't choose to do so if I won't run into oil problems. I can live with the 1-2% of oil circulating with the refrigerant.

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The problem we encountered was that the oil refused to separate. Just the opposite of the usual problem, i.e. failure to return. It's a new one on me.

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I have read the thread. It still surprises me because I don't see how AB oil can get carried on perfectly by a low speed vapour stream. Oil can dissolve in liquid, yes. But not in vapour, so it must separate. If it doesn't, a strange thing is happening.

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Originally posted by Gary Lloyd
POE is compatible with all of these refrigerants. No oil change is needed for the prommie.

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no

r401a, r401b, r402a, r402b, r403b, r408a, r409a and r409b need A or mixed A/M oil, no POE or M oil. all these refrigerants are drop-in-refrigerants.

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no

r401a, r401b, r402a, r402b, r403b, r408a, r409a and r409b need A or mixed A/M oil, no POE or M oil. all these refrigerants are drop-in-refrigerants.

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While AB or AB/mineral mix is usually recommended, POE is compatible with all of the above.