I think that there are a lot of: scare tactics, mis-information, and uninformed techs running around.

There are all sorts of alternatives to R-12, each with their own drawbacks. I'm a bit rusty, and this is all from memory.. but please correct me if I'm blatantly wrong anywhere.

First there's R12. Sure, it's around but it's expensive because we can't make any more or import it from elsewhere. It's nice because it's not a blend so you can top it off easily, and it's compatible with a stable lubricant (mineral oil). It's not flammable per se but it is (supposedly) damaging to the ozone layer and it can become a nasty nerve agent under the right conditions.

Then there's R134a. It's not damaging to the ozone layer, but IIRC it does contribute to smog. R134a has higher operating pressures, is more prone to leaking (smaller molecule), and is not compatible with the nice stable mineral oils used with R12. Instead, you've got two or three basic types of lubricants that you can use (but they are incompatible with each other and I believe in some cases mineral oil as well). One or both types are hygroscopic (like brake fluid) and this creates some nasty problems with moisture remaining in the AC system (and IIRC, R134a also forms corrosive acids when exposed to moisture). The reason that R134a requires a different lubricant is because it simple will not mix with mineral oil. R134a will not form nasty byproducts when introduced to mineral oil (unlike say introducing R12 to some of these alternative lubes or water to R134a).

Then there are the flammable hydrocarbon blends (like Duracool). Sometimes they're as simple as just putting propane (Hank Hill eat your heart out) in the system. Sometimes they're blends including other common hydrocarbons such as butane. They're illegal in 15 states, and I believe otherwise they're legal to use as R134a substutites but not R12 systems. Whether or not the flammability is a risk you want to take is something you should think about. Keep in mind that the various pressurized lubricants used in an A/C system are also flammable.

Then there's the non flammable hydrocarbon blends. Basically the same as above, but certified as safe by the EPA because of additional components that deal with the flammability issue.

Then there's R22. R22 is found in many products such as HotSpot. R22 is terrific, and regarded as safe by the EPA. However R22 is incompatible with the existing hoses and seals. You are required by the EPA to install barrier type hoses with blends containing R22. You'll also need to go thru and make sure your seals are compatible with R22.

Then there's R401c. Judging by what I've read it uses a lubricant that's not hygroscopic, has a sizeable installed base, and it's not flammable.

I found some interesting discussions here:
http://yarchive.net/ac/politics.html
http://www.rezine.net/Alternative refrigerant.htm
http://www.aircondition.com/wwwboard/alternative/current/7678.html

You can download some EPA certification prep material here (it's nice because towards the end it's got a table listing the various alternative refrigerants:
http://www.escoinst.com/Section609.htm

The big problem with these blends is that (rightfully so) the EPA regs require all sorts of separate equipment with incompatible fittings to hold the various refrigerants. It's much easier for a shop to standardize on two (R12 and R134a) than to purchase all sorts of equipment for the large variety of alternatives. You see many shops not want to deal with such systems not because the alternative refrigerants are bad, rather they want to avoid the cost of purchasing and maintaining extra equipment.

So, if I ever get around to fixing the AC on either of my cars, I'm not going to go with R134a. However, I would be upset with the shop if they told you they were going to install R12 and did not. If you can find an honest shop that will deal with the blend, don't worry about it. I believe Freeze12 is indeed more or less compatible with both mineral oil and the existing seals in your AC system.

- alex

'85 244 Turbo