Look under the hood. If your car had R134 fitted by a previous owner, it has a sticker. If it still has the R-12 it came with, you cannot buy refills anywhere, they are no longer available, it is illegal to manufacture R-12, and only a licenced a/c fitter can refill your system with recycled freon, after he ensures there are no leaks. It is probably cheaper to go to the shop and have your system fitted for use with R134. It is not a job for the driveway, as the old refrigerant has to be reclaimed in a proper manner.