View Single Post
Old 04-16-2011, 09:25 AM
vstech's Avatar
vstech vstech is offline
Join Date: Mar 2006
Location: Mount Holly, NC
Posts: 26,721
Originally Posted by francotirador View Post
Hello: I have a 1990 300SE and I would like to revert the system to R12. It was converted to R134 by the original owner. I read a long thread posted hereon where the original question was essentialy "how do you convert back to R12 from R134?" That question was posed a few times during the thread and it was really not answered.

So, please tell me, how do you convert a system from R134 to R12? The compressor I have is good for both types of refrigerant. I understand a different oil must be used. I know the drier has to be changed and the correct amount of R12 must be introduced into the closed system. I imagine the Schrader valve fittings must also be changed.

However, what I don't know is if there any other fittings, seals, hoses...that must be changed for use with R12?

If you would post the details of the R134 to R12 conversion I, and many others, would greatly appreciate it.

Thank you.

Great question.
several levels of answers can be dependent on what the 134 "conversion" entailed.
first, the Oil in the system. if you do not know what kind was used, it's best to replace the compressor, the expansion valve, and the compressor manifold, with the dryer and flush the remaining coils with oil/refrigerant flush, then add the correct amount of mineral oil to the system, pulling a hard vacuum, then weighing in the correct volume of R12.
this is the BEST method to convert back to 12.
PAG oil is not compatible with R12, Ester is. if you don't know, it's best to assume PAG was used, and do it right. however, since doing it wrong will destroy your compressor, requiring you do do all that stuff, if the wrong oil is used, and will not if Ester is in there, simply evacuating the refrigerant, measuring how much oil came out with it, and replacing that with the same amount of ester oil, then flowing the weighed amount of R12 will put the system back to R12. however you will still have the 134 fittings on the system... if you try to remove them, you can damage the lines (don't ask how I know this) this is why it's needed to replace the compressor manifold.
then lastly the 134 sticker needs to be removed.
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Last edited by vstech; 06-06-2011 at 06:06 PM.
Reply With Quote