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  #1  
Old 07-09-2003, 02:33 PM
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Join Date: Sep 2001
Location: Queens, NYC
Posts: 158
'88 420SEL A/C R12 vs. R134

My '88 420SEL (60K miles) was converted to R134 freon by the previous owner. Last summer, the A/C was weak (almost non-existent in 100 degree weather) - this year it's even worse. It occaisionally blows cold at highway speeds if its less than 70 degrees out. I'm guessing there may be a leak, however it is my intention to convert the system back to R12 freon, which one can purchase for about $20/lb on ebay these days. Although many shops recommend using R134, I'm tired of sweating in the summer and would prefer to spend the extra money to do the job right (using the refrigerant that system was designed for).

So far, I've learned that the filter/drier and expansion valve must be changed and the entire system should be flushed or cleaned out to remove any traces of R134 oil. Does the compressor need to be replaced, or removed for cleaning? Can anyone give me some insight on exactly what should be done in order to ensure my efforts are succuessful?
Thanks.
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2003 S500 Black/Charcoal
1990 560SEL 61k Arctic White/Grey

SOLD:
1988 420SEL Black/Palomino Sold @ 85k
1987 420SEL Midnight Blue/Grey
1986 420SEL Diamond Blue/Grey
1983 380SEL Champagne/Palomino
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  #2  
Old 07-09-2003, 02:45 PM
it leaks, its german
 
Join Date: Mar 2002
Location: raleigh nc
Posts: 1,111
First off make sure the duo valve is not leaking. Then install a 134 expansion valve and dryer, make sure the compressor is not weak and charge the system by output temp, not weight. Also make sure there are no leaking elements and the car has the dual aux fan set up.

Then make your desision on going back to 12. I think if you get the system right it'll cool great.



Joe
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  #3  
Old 07-09-2003, 03:41 PM
LarryBible
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When reverse converting, you do indeed need to totally flush the oil out of the system and replace it with mineral oil. Flush everything in the system with solvent except the compessor. Flush it a few times with mineral oil.

Then replace your expansion valve and r/d then evacuate and charge. Going back to R12 will be a worthwhile step.

Good luck,
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  #4  
Old 07-09-2003, 05:50 PM
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Join Date: Sep 2001
Location: Queens, NYC
Posts: 158
Thanks for the advice.

I spoke to my mechanic and he insists that removing the compressor is overkill. He wants to clean out the system through use of compressed nitrogen. No mention of flushing with solvent.

Additionally, he said that polyolester (sp?) oil is compatible with both R134 and R12, thus no need for concern.

I can't talk him into flushing it as you suggested, Larry.

Now what? Find another mechanic?

I'd just do it myself if I had all of the equipment, since no one else wants to follow directions...
__________________
2003 S500 Black/Charcoal
1990 560SEL 61k Arctic White/Grey

SOLD:
1988 420SEL Black/Palomino Sold @ 85k
1987 420SEL Midnight Blue/Grey
1986 420SEL Diamond Blue/Grey
1983 380SEL Champagne/Palomino
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  #5  
Old 07-10-2003, 08:44 AM
LarryBible
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There is a myth that Ester oil is compatible with 12. I would agree that a TINY AMOUNT of ester staying behind would not hurt, so maybe it is compatible in that way, but don't use Ester solely in an R12 system. Flushing with dry nitrogen will NOT remove the oil. It could be that you could flush the compressor with mineral oil without removing it, but then how will you empty the compressor so that you can measure in the right volume of oil. This is important, too much oil could lock up the compressor and too little will wear it out.

I can't tell you whether you should find another tech, but I sure don't like what I'm hearing.

Good luck,
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