R12 vs R134 questions - PeachParts Mercedes-Benz Forum

bob_98sr5 · #1 10-17-2007, 05:36 PM

Ok, going through about 7 threads leaves me more confused

I read one post that says "if your AC lines are the same size, then you have a R12 compressor". However in another thread, someone said "thats not necesarily true". this leads me to believe that:

1) the mercedes AC compressor is capable of handling both R12 and R134A
2) That some indy shops put in R134A into the AC compressor without changing the lines (when they should have)

So please can someone clear the air for me? Questions:

1) what is the definitive way to tell whether or not my AC compressor is rated to take R12...or is there a mechanical difference between an R12 capable and an R134 only capable AC compressor?
2) Is there an ID plate on the compressor itself? How do you tell? I could not locate any such plate on mine, but then again, there's a lot of grime down there.

Thanks,
bob

rrgrassi · #2 10-17-2007, 05:43 PM

If the car was initially charged w/r12, then the replacement compressor can take r12. R134 operates with higher pressures, so the compressor's mfg needs to state if it can handle r134. Typically, small hoses are the high pressure lines and the large ones are low pressure, but that is not always the case. On the w123, the lines leading to and from the compressor are large, but the small ones leave the condensor, drier and expansion valve. I have not traced the large high side to see where it's diameter is reduced.

bob_98sr5 · #3 10-17-2007, 07:05 PM

rr,

thanks for the explanation. makes sense, though it seems there is no hard/fast rule re hose diameter and its relation to the actual compressor.

im really going to have to look carefully at the compressor itself. gotta get down and dirty tonight. that said, its getting colder here out west, so the motivation is somewhat lessened

FRANKNBENZ · #4 10-17-2007, 07:43 PM

I have 85s with Frigidaire R4 radial compressors so this may not apply.

Guess you are not the original owner. Some things to check for:
+ Data plate on the compressor, then google what you find.
+ The R4 will handle both refrigerants, but as our colleague states, R134a operates at less volume but greater pressure.
+ Flexible part of the lines and O-rings are important. OEM R-12 lines, rings will handle the "fat" R-12 molecules. They will leak the "skinny" R-134a as these molecules will permeate through the material. The reverse is not so, that is, if your system was truly converted to R-134a, the flex lines would have been replaced to various materials whose molecular structure is "tighter" -- able to hold in the R-134a...and, of course, the fatter R-12.

I will be retro fitting such a system on Gray Ghost next spring (cold here too!)

Good luck.

zeke · #5 10-17-2007, 08:24 PM

One of those threads may have been mine.....I have a compressor that says r134a, but the PO (also original) said he had never changed it from r12. To see what the compressor said I got on my back under the car and wiped the label on the compressor (driver's side under the horn). Also there was no sticker indicating a conversion. In fact, he loaned the car out for a bit while he was overseas, and that person did change it out.....Found out when I took it to a mechanic who said he could shoot r12....but the fittings were r134a!

Seems the fittings are the best indicator of what's inside?

jkoebel · #6 10-17-2007, 09:03 PM

Quote:

Originally Posted by FRANKNBENZ

+ Flexible part of the lines and O-rings are important. OEM R-12 lines, rings will handle the "fat" R-12 molecules. They will leak the "skinny" R-134a as these molecules will permeate through the material. The reverse is not so, that is, if your system was truly converted to R-134a, the flex lines would have been replaced to various materials whose molecular structure is "tighter" -- able to hold in the R-134a...and, of course, the fatter R-12.

R-12, dichlorodifluoromethane
R-134a, 1,1,1,2-tetrachloroethane

R-134a is "bigger" by almost double.

That's not to say something about the seals doesn't hold one better than the other, but, if it was R-134a being too small to stay contained, that's probably not the case.

jbaj007 · #7 10-17-2007, 10:14 PM

1.) ANY R4 compressor that you can get your hands on now will handle R134a or R12. Unless you have an original R4 from a 1976 Impala don't worry about it.
2.) Hoses that have been in service with R12 and mineral oil for any length of time will be essentially impervious to R134a. This has been accepted for years now. There can be theoretical discussion about it, that's fine, but in practical use it's a closed subject. Of course NEW hoses should be barrier type.
3.)R134a is a SMALLER molecule than R12.

rfdillon · #8 10-17-2007, 10:30 PM

Have you thought about using Freeze12, a hybrid refrigerant that is a drop in replacement for R12? Much less expensive and works well here in hot and humid Houston, TX.

jbaj007 · #9 10-17-2007, 10:38 PM

Composition of Freeze12 is just R134a plus some R142b to carry the mineral oil.

MSDS info.
Freeze12 ~75-90% R134a
~10-25% R142b

sailor15015 · #10 10-17-2007, 10:57 PM

Try Enviro-Safe Refrigerants.

jkoebel · #11 10-17-2007, 11:11 PM

Hmm.

R134a is smaller than R12.

I find that odd, but stand corrected.

Matt L · #12 10-17-2007, 11:23 PM

Quote:

Originally Posted by sailor15015

Try Enviro-Safe Refrigerants.

Hydrocarbon refrigerants are not legal drop-in replacements for R12 or any other ozone-depleting refrigerant for mobile use.

#13 10-17-2007, 11:50 PM

Just use the R-12 it was designed to use.

tangofox007 · #14 10-18-2007, 12:11 AM

Quote:

Originally Posted by Craig

Just use the R-12 it was designed to use.

That's just too simple and too effective!!!

WD8CDH · #15 10-18-2007, 01:19 PM

Personally, I prefer the hydrocarbon replacements over R-12. Much better for the environment than any other option and possably even more efficient than R-12. It's legal to replace R-134 with a hydrocarbon replacement in most states.