I don't think that r12a has any global-warming potential (GWP) but it does cause ground-level ozone and smog. It would be better to burn it than to release it unburnt.

134a has a GWP of 1500, meaning that one pound of the stuff has the effect of 3/4 ton of CO2. That's why Canada likes you to use r12a or such.

It is clear that hydrocarbons can perform a refrigerant cycle. The problem with products like r12a is that they are blends, whereby several gasses with different properties are blended to achieve performance as similar to the original refrigerant as possible. But the various parts have variously-sized molecules, and the proportions will not stay. Thus, you cannot top off with a blend; you must evacuate and recharge for any service.

It is also clear that an air conditioner system can be designed for any product which can be coerced into a phase change, whether it be a chlorinated or hydrogenated fluorocarbon, a hydrocarbon, or even ammonia. It's been done for all of them, and more.

The reason that you don't want to run hydrocarbons in your AC is simply because it was designed to use another product.

I won't argue about the use, and what the system is meant to use. I have an availability problem... There are specialized shops that deal with R134a, and the last time I was in one of them, I might as well have put a down payment on a new s class...
As far as I'm concerned, baby steps. The first thing to probably try would be to see if I could evacuate the oil in the system and put in weighted charges of oil and refrigerant. Is there a way to evacuate the oil without opening the system??

The only way to evacuate the oil is to open and flush the system.

I recommend a new condenser. They're fairly inexpensive, easy to replace, and about impossible to flush and purge.

Lets mention before we get too far that hydrocarbons used in moving systems are illegal in many states....and that it may be hard to find shops who can and will work on them..
and whatever you use... the EPA has DESIGNATED valves which must match what you have in your system plus decals saying what is inside...

A lot of people are not smart enough to put together the concepts of having basically unprotected flammable gas under pressure at the very front of an automobile and the UNnecessary risks of fire potentially in even just fender bender category accidents...

http://www.epa.gov/ozone/snap/refrigerants/hc-12a.html

People should watch " The Great Waldo Pepper " ....to really understand the concept.

Those designated valves only apply to CFC replacements. If you have an OEM 134a system, you can replace the refrigerant with hydrocarbons without changing fittings.

I'm well aware about the risks of a hydrocarbon in the AC system.... refrigerants are all but impossible to get in other than a 50 pound bottle, and that's a really pita and $$$$.
Last times I checked, just a recharge of the system with R134a was $300+. I'd rather use the duracool and worry about the flash in a collission when that happens...
It takes quite a temp to make a flash of that stuff anyways...
I heard that R134a actually burns at a lower temp anyways... I doubt the A/F mixture would be right in a collission to cause a flare up...

In Canada, the R134a fittings are the correct fittings for hydrocarbon refrigerants...

yes.
after verifying no leaks are present, vent the nitrogen, then attach your vacuum pump, and evacuate the charge, and refill with the correct volume of refrigerant.
I use 30 lb jugs, of refrigerant, so I can charge with the system OFF, the correct volume into an evacuated system.
most DIY types need to use 12 oz cans, and each time the can is opened, air gets into the manifold, and the car, and some of the refrigerant is lost.

to properly recharge a system, a reclaimer is needed, and a charging station, or at least a jug of liquid refrigerant, and a scale...

nitrogen is harvested from the air, so putting it back is ok. (our atmo is around 80% Nitrogen) the 4oz R22 is allowed to be vented by the EPA

Well, I'm still trying to understand exactly what I can do with the 134 fittings. Both high and low side 134 fittings were installed in my car when the R12 to R134 conversion was done. I want to change those fittings back for use with R12. Can I just get new Schrader valve inserts and the correct cap for R12, or is there more to the fittings than that?

Also, I see kits available with all of the green o-rings/seals for conversion to 134 from R12. However, I haven't seen any for reverting to R12 from 134. Does anyone know if and where they're available?

I really want to get this project done as the 134 just isn't cutting it in this South Florida heat.

I've ordered a new compressor, new drier, new expansion valve and new manifold hose. I have an R134/R12 Recovery/Recharge unit and 20 pounds of R12. So, I'm good on that front.

All help is greatly appreciated.

if you ordered new manifold, it should come with new R12 fittings on it! done.
the problem with trying to remove 134 fittings from the R12 fittings that came on our cars is they are lightly brazed onto the steel lines... usually the force needed to remove the adapters will rip the brazing, and you'll need to replace the entire manifold (and change your shorts when the MASSIVE amount of 134 and oil dumps out of the broken lines.

Sorry, this thread is strictly for discussion of proper techniques for use with legal and standard refrigerants.
Duracool discussion is only for the Canada members that cannot obtain 12 or 134... (although they use the 12a refrigerants, which are 134 blends with other chemicals for lower flash points...)
I'll have to move this question to the general discussion section, and let you question it there. sorry.

There are huge great threads in the archives on this...
but in short.... you have to take the fittings apart .. at the orings you would replace anyway... and use some force.. not much is needed... to push some proper solvent through the lines... in the FSM there is a machine which filters and re uses the flush and shows when it must be discarded....
there are ' flush gun's... sorta like paint cans with a way to attach some compressed gas... air from your air compressor is not the best to use as it is seldom really dry....certainly not as dry as Nitrogen or Argon ...
The MB AC FSM even specifies which direction to send the flush through on the lines... without the machine you would want the ends of the lines to be in a bucket to catch the fluid use...and try not to breath them of course... it is not so expansive that you can not use it as a ' one time ' expendable.. for such an important item as a long lasting AC system...

I was doing some reading, and is it possible to replace the TXV in a 95 S320 with a VOV?? Something like this one?? http://www.aircondition.com/vov/
If there is one for this car, where would one buy it??

BTW, I have an air drier on my compressor... I do some painting here and there....