Retrofitting a R12 A/C system?

So my cousin just bought a 1993 Honda Civic Coupe and like most older Hondas, the AC doesn't work and on top of that it also needs to be retrofitted since it uses the old R12 system. I have some experience working on cars but need a second opinion on this one. I would much rather do the work myself that way I learn in the process as opposed to just paying someone to do it and call it a day. Buying and installing the new fittings is not a problem, the refrigerant is what's got me confused. I know R134A is not compatible with R12 and can cause problems if the system is not evacuated properly. I can have the whole system evacuated for 20 bucks which will solve that problem. Oil is also not a problem opted to go with ester 100 and use the adequate volume for the car. My question is, is it more straight forward/ Convenient to just use R12A or just go with R134A? I'm aware that these refrigerants also have a different mass and exact amounts have to be calculated. If I opt with R12A, would I need to even evacuate any remaining R12 from the system? Now of course I'm assuming that there are no leaks in there and will have to do a test to see if it holds vacuum but if it doesn't that will just be another problem that I have to resolve. Any feedback is appreciated, thanks in advance.

It's illegal to install R-12A in a vehicle. It's highly flammable made with propane and butane. Get in an accident, rupture a line and Ka-Boom.

For a real retrofit you'd also want to flush the system, replace the hoses and all the O rings with newer barrier hoses and R-134a compatible O rings and replace the receiver dryer.

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

I'm not sure what Stpaulguy smokes, You can buy R-12 on Ebay for cars it is a bit more pricey. He is also delusional with some ranting about cars going kaboom. All cars used R-12 up until the early 90's they did not go ka-boom in an accident. Most of the time the new fittings are put on and system is evacuated and the new oil and R134 is put in. If it works it will last for a few years at most. If any work is done on the system all the orings and compressor should be replaced. May not be worth it on a 1993 car unless he wants to keep it forever though.

As Stpaulguy says, R12A (Duracool) is legal to sell but illegal to install, and is extremely dangerous.

R134a conversions are a hit or miss thing - as the video sc0rpio_nytes shows, there's some very bad information coming from very well placed sources. Such a conversion will work for a while before the compressor dies of inadequate lubrication. See the first source for the effect of HFCs entrained in ester oil used in R12 systems on PAG oil.

For a decade or so after R134a was introduced R134a retrofit was the way to go. There was still a lot of life left in most of the systems and servicing with R12 had a very dark future. Today the economics have reversed; there's still enough reclaimed R12 to meet demand at something above $50 per lb, less than you would spend on a proper retrofit. The odds of the car being around long enough to need another major A/C service are pretty long.

First you need to repair the a/c system.
Why doesn't it work?
Did the R-12 leak out?
Is there some other problem.
Having some tools and know refrigeration system knowledge is not enough.
You are asking about 2 very important things.
Repairing the system. (you need knowledge and equipment)
Retrofitting the system. (hopefully the system should work first!) You still need knowledge and equipment. You can't just use some cans of R-134a from the auto parts store. You at minimum need a vacuum pump and a set of a/c gauges.