How hard is it to convert back to R12 from R134? - PeachParts Mercedes-Benz Forum

Hatterasguy · #1 04-08-2007, 04:42 PM

The SDL was converted to R134 back in 1994ish by MB of North Haven. I have no idea what they changed, but form the looks of it the hoses are most certainly newer, and the compressor probably isn't original. Since a MB dealer did it they probably changed a lot, dealers always seem to.

My complaint is the currant AC sucks, on hot 100 degree days you have to blast it all the time to get marginal cooling. On cooler days it works fine, its just that we usualy get a couple of weeks of amazingly hot weather every summer and it can just barely keep up. I replaced the AC condensor and they charged it up at my dads work about two years ago. As far as I can tell the system seems to be working fine, it just can't keep up. I replaced the Kilma and push button head unit with rebuilt ones, all the flaps seem to work, it seems to hold temperature etc.

So the shop that does the company vehical's at my dads work probably has their 609 cert and can get and use R12. So how difficult is the conversion back? Do they just need to vent the system and refill it with R12?

300SD81 · #2 04-08-2007, 04:51 PM

SDL = W126, right?

Just did my AC, pretty easy job except for getting the expansion valve off without crowfoot wrenches.. Just disconnect everything, flush, replace the receiver/drier and expansion valve. Since your going from R134a to R12 and not replacing compressor, I think you have to use compressor oil to flush out the compressor. Remove the R134a service fittings and replace the valves or find a R12 can tap with a R134a connector, vacuum, and fill with oil and R12..

nhdoc · #3 04-08-2007, 04:54 PM

Converting back is much like the conversion to R134a, if it was done right. You'd need to replace the receiver-dryer, flush everything out maticulously to make sure all of the PAG oil is gone, replace that with the correct R12 mineral oil, evacuate and recharge. Is it worth it? Maybe. You might also have other issues though. The expansion valve may be clogged or the condensor fins might be clogged. I'd certainly check the condensor and make sure it is completely clean of debris and bugs and that the aux fan is working well and you can check the system by putting a set of gauges on it and seeing what the pressures look like. If the high side looks too high and the low side is too low you may have a restriction somewhere. In my SL it was in the screen at the expansion valve. Replacing the EV cleared it right up. The gauges are the best way to tell if the system is working right before you go changing it back to R12.

I am a huge proponent of keeping R12 systems R12, but once they have already been converted it might be more efficient to see if you can improve it enough to live with rather than undertake the re-conversion back.

#4 04-08-2007, 06:52 PM

I did it the easy way. I had mine converted to R-134 shortly after I bought it and the (original?) compressor seized (I know, I was an idiot). The R-134 performance was always marginal, OK below about 90F while driving, but not good above 90F and/or stopped in traffic. I just waited until the new compressor seized (about 100K miles) and had it restored to R-12. As I recall, I paid the shop around $1000 each time because just about everything had to be replaced anyway. The only real difference was paying the shop $50/pound for the R-12 (but I do get extra points in the "money pit" tread).

brandlj · #5 04-08-2007, 06:52 PM

My 86 300sdl was converted to R134a about three years ago. I live in hot, humid NE Louisiana and my system does just fine with the R134A once I replaced my two vacuum control pods that control the Recirc. function. My car also did not seem to keep up with the heat and humidity and I discovered that the two pods behind the glove box were not closing off the outside air when the recirc button was used. I replaced them and all is well. Also I clean the area between the radiator and condenser every spring to get all the bugs and junk out. Also make sure your auxiliary fan in front of the radiator is coming on when it needs to. That fan really helps in stop and go traffic. On my 89 BMW 535i I actually wired in a switch to bring my high speed fan on all of the time when I am stuck in traffic.
John

Hatterasguy · #6 04-08-2007, 09:03 PM

I replaced the condensor and the radiator a couple of years ago, both are still perfectly clean. All the fans work as they should, all the flaps do their things etc. I went through a lot trouble shooting the climate control system on that car, it works. The guys that charged it were good and the pressures are correct. I'm just used to American cars that will turn the cabin into an ice box on low. Old Mercedes just don't have as robust of an AC system. Its not that it doesn't work, I'm just picky and would like it to work better if possible.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=21B0XKG2A22318ZTYI&year=1987&make=MB&model=300-SDL-001&category=R&part=A%2FC+Receiver+Drier

So it looks like roughly $60 for the drier, which I can install. The shop at my dads work would probably charge me like $100 to flush it and install R12. Thats not including the R12 fittings.

300SD81 · #7 04-08-2007, 09:36 PM

Go to ********az for the drier, i think they have it for $20-something, the R12 fittings are there, you need to remove the R134a fittings screwed on them, and replace the valve cores. Flushing is pretty easy too, you can do that yourself. Don't install the receiver/dryer until immediately before you vac the system and charge

Edit:
Receiver Drier, $25
Expansion Valve, $19
Valve Cores, $1 each (need 2)
Valve Caps, $.50 each

Hatterasguy · #8 04-08-2007, 09:38 PM

Hmm in that case I'll talk to my dad and see if they will do it at his place.

#9 04-08-2007, 09:48 PM

Quote:

Originally Posted by Craig

I did it the easy way. I had mine converted to R-134 shortly after I bought it and the (original?) compressor seized (I know, I was an idiot). The R-134 performance was always marginal, OK below about 90F while driving, but not good above 90F and/or stopped in traffic. I just waited until the new compressor seized (about 100K miles) and had it restored to R-12. As I recall, I paid the shop around $1000 each time because just about everything had to be replaced anyway. The only real difference was paying the shop $50/pound for the R-12 (but I do get extra points in the "money pit" tread).

my god man, why don't you do the work yourself?? all the knowledge is here on the forum and it isn't that difficult to work on these cars. you probably make more money in the time you'd spend fixing it yourself?

Mercury · #10 04-08-2007, 10:03 PM

Most of the work is very easy, although time consuming. Diesel Giant has a write up that will cover you for the cleaning. Have a professional on tap for the evacuating, charging, and such. My local AutoZone loaned me a flush gun, I bought the flushing oil for cheap from them. Make sure that the flush oil is compatible with your new refrigerant (R12). Lots of time and compressed air will get the entire system clean(no more green stuff), just have a new set of o rings, and filter ready. I broke the temp sensor when installing, and had to buy another, got a new pressure sensor while I was at it.

300SD81 · #11 04-08-2007, 10:09 PM

I'm pretty sure brake cleaner is an accepted flush by alot of people... I used methanol in mine because I have a ton sitting around, and it boils very easily under vacuum...

deerefanatic · #12 04-11-2007, 05:36 PM

Not to hijack a thread but, I'm going to hijack a thread!

As you might know I'm moving my drivetrain to a new car body... My current car was converted to R134A by the PO. It does appear that the hoses have been replaced, and the correct R134A service ports are on the car, not screw-ins, looks like soldiered on as part of the hose assemblies..... The car doesn't leak or at least not much as I haven't touched the A/C system since I bought it in '05 and it still cools just as well as it did then (which isn't very well at all! )

I want to convert back to R-12 as I don't want to sink money into upgraded condensors and I also want the lower drag on the motor. But, I have no idea how this conversion was done.... I don't really know what freon is in the car, what oil is in it, what shape the compressor's in........ frankly, I don't know anything...... "Supposedly" it was a "proffessional" job...... But you know how much stock you can put in the PO...

What's the general advice? I've thought of using Freeze12, but I am holding off just because of the contamination factor on the equipment....

Of course, I could also always mix some Propane and isoButane in a 79%/21% mix and use that! ..... LOL........