R12 W/I freezer
Got a call on an older W/I freezer (R12 )that had recentley been converted to hotshot by another company. I guess its something I never thought about before until I checked out the LPC settings. Why would anybody have ever wanted to design a pumpdwn system on a freezer using R12? LPC cutout has to pump down into a vacuum and evap operates below atmospheric as well, especially after being converted to hotshot! (-20*F =5.7 psi "hg with 414b) Im sure theres alot of that out there (R12 pumpdown freezers) but why make life hard on the comp and have it operating in the vacuum? The case in question has an old K body cope and seems to have operated like that for years so... If one where to change oil and TXV and use say 404 would not the condenser then be undersized due to the higher operating pressure?
Last edited by dave1234; 06-07-2010 at 09:41 AM.
now i am just thinking out loud here
couldn't you just use less refrigerant and make it work
no because you need a full column of liquid
ya, after some previous discussions
initially i would think with the 404a your capacity would change bigtime
you need to stay with something close to the r-12 like 134a unless you want to redesign the thing
surely a better answer will follow this one
Of all the available interim replacement refrigerants to use in place of R12 for low temperature applications, R401B (MP-66) is the best one. It's still not as good as the original R12, but it will perform noticeably better than R414B (Hotshot) or any of the others.
You can't change to a higher pressure refrigerant like R404A because the existing R12 compressor's displacement is too big. R404A requires only about 2/3 the displacement to achieve the same capacity.
For example, a 1 hp KAL2-0100 will do about 3500 Btuh @ -10ºF/110ºF with R12. It's displacement is 313.0 cubic feet per hour (CFH). A 1 hp KAJ3-0100 will do the same 3500 Btuh at those conditions on R502 with a displacement of only 218.0 CFH.
If you were to try to use R502 (or R404A, which has similar performance) the R12 compressor would be attempt to pump at a rate of over 5000 Btuh and require a 1.5 hp, which would overload its 1 hp motor. If you replace the R12 compressor the proper displacement compressor, the existing condenser would OK.
Understood on the compressor part- but what about the low operating pressures in a freezer app for R12 and having to have the cut out in a vac for pumpdown? Wheres the advantage there over 502 (in terms of original design) when its obviously not good to run a compressor in a vacuum? Dont see too much 401B round here. Isnt it terribley expensive vs MP39?
From the compressor's point of view, it really doesn't care about the vacuum because it really doesn't see a vacuum. At 0 psig the compressor only sees 14.7 psia. That KAL2-0100 I mentioned was originally rated by Copeland for low temp R12 operation all the way down to -40ºF evap temps.
Of course, running in a vacuum poses potential system problems especially if there are low side leaks which would draw in air and moisture. That's really the main reason we don't like to run below 0 psig.
Guess actually starting a compressor in a vacuum is much much worse then pulling it into vacuum. i know R12 predates 502 so what was the advantage of 502 for low temp apps way back when?
I suppose most of all, R502 got you away from running below atmospheric pressure. After that, it allowed for a smaller displacement compressors and piping sizes to do the same job. Then I believe it was generally a bit more efficient...especially at very low temperatures.
Originally Posted by dave1234
I remember back in the 1950's, my father dealt primarily with R12 systems as it covered the gamut of applications...high, medium and low temperature.
But even then he had three tanks on the truck, because there were still a number of pre-R12 systems still running on either SO2 or Methyl Chloride...many of which eventually got retrofitted to R12.
Actually, R502's predecessor for low temp work was R22, which saw a rebirth for low temp about 20 years ago. R22 had the same advantages to those I mentioned for R502 but it's main problem was, and still is,its inherently high discharge temperatures.
A while back there was a thread in which you were evaluating 437A (MO49Plus). I don't have any experience with it, but from what I've read, it seems ideal.
Originally Posted by icemeister
Do you have any new experience/info to share regarding 437A?
Ice I remember the post. I remember you saying it wasn't available in the US at that time. Good to hear you've finally got some at last.
I've had to use it more often now as my R12 stock is almost depleted, well not more often because I don't do much these days. But I've had no problem with it as drop in. Can't say I've noticed it perishing seals or "O" rings though. I tend to check things like that when I've pumped down or decanted, to see if they're OK or not.
Used it in freezers as well with no complaints, I've just noticed that the compressor runs for a bit longer than when it had R12 in it, it still maintains a steady -18 deg C. But the customers are happy as it is a cheap solution, and buys them a bit more time for when the system completely dies.
One customer rung on a hot day and said he noticed the sight glass had bubbles in it. When I got there the system checked out OK and there were no leaks or low charge, the only thing I culd think of is the condensor coil had been changed sometime before. I just thought maybe its not the right one and not quite quite big enough to cope with very hot days or abnormal loads.
It turned out that a new member of staff who worked there had the door of the walkin freezer open to try double it up as an airconditioner. Never no bubbles problem reported after that.
50 & 60 hz but 100's worse
Ice answered your question in post #5 but I would like to add
R-12 was CHEEP period. It covered the entire field including A/C. Operating or starting near a vacuum was common.
I've worked on old Ice Cream WI's for Harry M. Stevens, 6” calk insulation belt drive compressor. When this box went down you would fix it and let it run for a day or two or until ice would form on the outside walls. (That’s how much moisture had saturated the insulation over time, the ice was your insulation) In the 80’s this box was 30 years old and still pumping away. No one cared about energy costs or the environment. R-12 was cheep and that’s what you used. R-502 cost more and slowly came into fashion. (Convert are you kidding this unit is older then you.)
Today is different, Energy costs are rising and manufactures build the cheapest operating unit and don’t care if it lasts. Get past the warranty period.
Ice, Myself, and several others on this site were used to working on equipment 20 & 30 years young. Not any more. I don’t know if were going forward or backwards.
MO49 Plus has been "available" to us here in the States for a couple of years now, but unfortunately it is quite slow in becoming "readily available". Nobody is stocking it...at least where I'm located.
Originally Posted by chilliwilly
Thanks for the input on you experience with it, Martyn. I knew you had MO49 (R413A) for quite some time, but didn't realize until today while doing some searching about, that you folks have been switched to MO49 Plus (R437A) as well:
Does this come as news to you too? I can no longer find any reference to R413A on the DuPont UK website. Hmmm?
As for the leaking seals, if you have been converting directly from R12 to MO49 then you should have no problem. The seal troubles exist because of the R22 component of most interim replacement refrigerant like R409A, R401A, etc. The R22 tends to swell the elastomeric seals. When you remove the R22 the seal then shrinks....and you've got a leak.
I haven't had any R12 stock for nearly 15 years.
Wasn't R12 the chosen refrigerant for domestic refrigerators for decades? Given their design (evap in freezer only), I suspect they all would've run in a vacuum as well. Nowadays I wig out if a see a system doing that.
As a side note, I've come across entirely too many converted systems where you don't know what's in them, so I've had to figure it out through investigation...OR just pull it, charge it up and LABEL IT prominently for the next guy.
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