I've got a 92 bonneville with the original a/c system and i'm wondering the cheapest way to get it working again, This has got to be the hottest weather i have ever seen and its torture with no a/c.

Unless you've got a set of gauges and are willing to flush the system, you'll have to pay a mechanic to convert it to R-134A

if i wanted to do it myself what would the process be and what would i need.

Local auto shop sell'* kit'* to convert the system. I paid like $50 for the kit. I has no real gauges to check the system. You will have pay someone to get the r-12 In most area it illegal to just dump in air. Which the reason it usallay best to get done professional. I lucky(sort of) out my car the r-12 had all leaked out. Just for fyi the non lucky part is that my a/c compressor worked for month then I hard some ugly nosies from it(had the hood open at the time) that was it. If compressor is bad the can cost lot on my 92 it is $500 for new. I am going to go the junk yard and pick when up for $70. They siad they would give me 30 day warranty. I hope this helps.

Sorry at my local auto shop the said they would sell my professional set for $70 or 130 I can't remerber ,but they would also lot rent to which is free If buy the parts from them.

What year did they stop using r12 and start using r134a?

I think between like 93-95 the transition from r-12 to r-134a occured.

95. Some 94s got R134a as well, but it was mandated that all cars had to be on 134a starting in 95 model year.

X2 95 is the mandate year