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  #1  
Old 05-15-2007, 02:15 PM
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'86 420SEL: Converting back to R-12

Hi, my system was converted to R-134 by the PO and performance is not good, but it does cool some so I know it basically works. I know the compressor seal is leaking from the green oil dripping out. If I start repairs, I want good performance when I am finished at least. I need to know what to change to convert it back. I am suspicious that the conversion was not correct; for one thing they installed a low-side R-134 fitting on the high side (egad), so I think probably nothing else was changed. Assuming this, can I flush, then install new lube along with a new compressor, then charge with R-12? Advice is appreciated.

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  #2  
Old 05-15-2007, 04:38 PM
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You will need to fix the compressor seal, then remove the R-134 fittings if possible. Next you will need to flush multiple times in both directions (to ensure complete removal of PAG or ester), dry thoroughly, and put in the correct amount of mineral oil before charging the system. You should replace all o-rings too while you have it apart. The last step before buttoning it up is to replace the receiver/dryer. Converting back to R12 is a big job, but it can be done and will definitely cool much better. I hope to do my converted 380SE sometime this year.
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  #3  
Old 05-15-2007, 05:08 PM
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Ideally, you'll want to get the expansion valve out and replace it..often I find that poor R134a conversions gum up said valve.. Flushing past this valve is questionable @ best.

I assume you'll be pulling the compressor off to get all the old oil etc out.

Jonathan
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Old 05-15-2007, 09:36 PM
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This http://www.hecat-inc.com/flush_gun.htm is really cool, but pricey. If someone gets one, can I borrow it?
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  #5  
Old 05-16-2007, 10:39 AM
david s poole
 
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if you want to make this a/c really perform when you change it back ,remove the condensor and clean off all the black paint so that you have shiny tubes.[mag wheel cleaner works very well spray on leave 5 mins and wash off,dont forget to seal ends from water intrusion]
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  #6  
Old 05-16-2007, 02:06 PM
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Quote:
Originally Posted by david s poole View Post
if you want to make this a/c really perform when you change it back ,remove the condensor and clean off all the black paint so that you have shiny tubes.[mag wheel cleaner works very well spray on leave 5 mins and wash off,dont forget to seal ends from water intrusion]
David, great suggestion which I saw you post in another thread as well. Do you think there'd be any harm in using a spray-on paint stripper, letting it soak for 5 minutes, and then hosing off? Or would it be too agressive on the brazed connections?
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  #7  
Old 05-16-2007, 02:28 PM
15289577
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Just so you know...R-12 is no longer available on the open market. Good luck finding some.

R-134 may not be quite as good as R-12, but it doesn't destroy the environment the same way R-12 does and it's extremely cheap by comparison (mostly because it's still being made). Also, anywhere you can (leagally) buy R-12 from require that you have an A/C service license. Even then it's still $100/lb or more.

There is an R-12 substitute on the market that advertises itself as a form of R-12. Don't be fooled, it's not actually R-12. It does work a slight bit better than R-134, but it's still quite a bit more expensive.
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Old 05-16-2007, 04:12 PM
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R12 is available all the time on Ebay..$25-$30 per pound.

I bought a 15 lb. "keg" for ~ $8/lb.

I missed this by napping.. less than $3/lb.http://www.peachparts.com/shopforum/showthread.php?t=182232&highlight=R12 post #5

You may not find these deals , but it's out there all day, everyday.

Most major refrigerant suppliers have 30 lb. tanks in stock.
Ebay and some auto parts stores have the little cans as well. You do need a 608 or 609 cert., though. $25 online test gets you the cert. for life.
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  #9  
Old 05-16-2007, 04:29 PM
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I normally scour the bay and can get about $10 per can. I have also bought from Napa - they have a ton of it back behind the counter, though it is $35 per can. Just present your 609 and you're good to go.

R12 is not hard to get at all.
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  #10  
Old 05-16-2007, 04:35 PM
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Or you could do the environmentally friendly, correct, cheap, and easy thing and just charge it with the very easily available R134 and suffer the oh-so-slight loss of performance. My car only takes 2 minutes more to cool off than it did before the switch and I definately havn't died of heat exhaustion yet.

I don't like to argue about things quite so dumb, but here's my on-topic advice. Don't bother switching back to R12 if the system works and has already been switched to R134a. It will save you problems and headaches later. Plus, why fix something that isn't broken?
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  #11  
Old 05-16-2007, 04:50 PM
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Quote:
Originally Posted by Randy View Post
I am suspicious that the conversion was not correct; for one thing they installed a low-side R-134 fitting on the high side (egad), so I think probably nothing else was changed.
Your suspician that the conversion was not done correct is probably accurate, but the reason that the low side fitting was attached to the high side is this: mercedes doesn't have different size schrader valves on the low and high sides like all the american cars out there do. If you buy the new fittings from napa or anywhere other than a mercedes dealer, the high side fitting isn't going to fit because the schrader valve is too big. To remedy this, buy the correct adaptor fittings from a mercedes dealer. They ran me $10 each, but they are also of much higher quality than I've found anywhere else with the added bonus that they fit. I checked fastlane for the part and didn't find it...

The other part that should have been changed was the accumulator/drier. Another thing that really could have been done wrong was if the PO mixed the two refrigerants or different kinds of oil. These things could potentially be bad. If suspected, it may be a good reason to do a system flush and/or drain and refill of the compressor oil.
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  #12  
Old 05-16-2007, 05:33 PM
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Originally Posted by 15289577 View Post
...suffer the oh-so-slight loss of performance. My car only takes 2 minutes more to cool off than it did before the switch and I definately havn't died of heat exhaustion yet.
The original poster did not say where he was located, or perhaps I missed it. I see you are from Omaha, NE. Furthermore, you are new here. A tip for you: R134a vs. R12, conversion vs. no conversion vs. converting back to R12 etc. can stir very passionate debate at this forum. Just ask LarryBible! The consensus is that systems designed for R12 will work with R134a, but very poorly depending on where you're located.

I am in Texas, and I will tell you that the vent temps on my R12 car are a full 10 degrees colder than those of my professionally-converted R134a car. They also take about 5 to 10 minutes longer to get there, depending on how hot it is outside. In Omaha, where it may hit 95 degrees, that might not be a big thing, but here in DFW, when it can hit 115 in stop-and-go traffic, you need every degree you can get. If a system was designed for R12, it is going to be very difficult for it to cool as well without that refrigerant in there. Yes, I know expansion valve, P-flow condensor, etc. can be swapped in, but rarely will the performance ever be as good as if you just leave the R12 in there. Not to mention the cost of these parts and all the labor associated with changing them out - all for the price of a couple cans of R12 that can be had for $30.

This guy's situation is a little different, since he is considering converting back. I say go for it, as I eventually plan to convert my own R134a system back to R12.
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  #13  
Old 05-16-2007, 05:37 PM
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I should also point out that with a converted R134a system, the head pressure on the compressor can be nearly double that of the original R12 setup, so your compressor will be put through twice as much wear and tear as if you were to just leave it as R12. So we are talking about way more than an "oh-so-slight" performance loss.
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75 W114 280
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  #14  
Old 05-16-2007, 09:14 PM
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Quote:
Originally Posted by 15289577 View Post
Just so you know...R-12 is no longer available on the open market. Good luck finding some.

R-134 may not be quite as good as R-12, but it doesn't destroy the environment the same way R-12 does and it's extremely cheap by comparison (mostly because it's still being made). Also, anywhere you can (leagally) buy R-12 from require that you have an A/C service license. Even then it's still $100/lb or more.

There is an R-12 substitute on the market that advertises itself as a form of R-12. Don't be fooled, it's not actually R-12. It does work a slight bit better than R-134, but it's still quite a bit more expensive.
The license to buy it is easy to get, and costs very little. There's little reason for someone who owns an old car to not have it.

The stuff certainly does not cost $100/lb. Nowhere close, although the prices is going up by 50 cents a year per pound due to taxes. There isn't really a scarcity of it, since most older cars have been converted or scrapped.

However, if you do have a system that was converted to 134a, it is legal (in many states) to install a hydrocarbon refrigerant (it's not legal to install it in an unconverted system). That is a mix, so small leaks will cause you headaches, but that stuff is very cheap and works well.

The things you're talking about are refrigerant blends, and suffer from the same problems in the presence of leaks. The different constituent gases leak at different rates, and throw the mixture off.
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  #15  
Old 05-17-2007, 11:03 AM
david s poole
 
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GMERCOLEZA,the paint stripper should work ok.use your best judgement as you watch the paint bubble and don't leave it on too long.this mod will bring head pressure down by about 25psi.

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"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
http://www.w108.org/gallery/albums/A...1159.thumb.jpg
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