Kits are available at most auto parts stores. Unless you have the proper tools and skills, I recommend you have this done by a professional. It is illegal to release R12 into the atmosphere. Any R12 left in your system, can be reclaimed. Make sure you receive reimbursement for the R12 they remove. R12 is extremely expensive and valuable. Don't give it away.
If you mix r12 with r134 air conditioning system, it will cause a high pressure in your airconditioning system and eventually damage the compressor and the evaporator. R12 is only for r12 aircon and something with r134, it can't be mix.
It came with R12 but due to the price of R12, I would convert it over to R134a. You need to fix the leak before the conversion.
Why would you want to even consider doing this? R12 is no longer in production and as such it cost almost 4 times as much as R134. But to answer your question, use R12 in a R134 system and you will destroy the compressor as the oil is not compatible with R134 oil.
Its probably an R12, That's an expensive proposition from the point of R12 or conversion to R134. Get professional service, AC is not novice level stuff.
R134a.
Should be R134
R12 Unless it was converted over to R134. There should be a decal if they did the conversion.
R12 134A pre 1996 is r12, after is r134
R134a
r 134
If if it a 1995 or older then it came with R12 installed. 1996 can be R12 or R134. 1997 up, it has R134/R134a. If you suspect it had R12 look for a label somewhere on the A/C unit signifying it has been converted. If you find it has R12 and is leaking and needs repairing, after the leak is repaired, convert it to R134a. R12 is far too expensive to use.
First of all, you don't use R12. Rather, R134 which has the oil included.