72 scamp factory air -Do i have to convert?

Like others have said, have the system checked. They can pressurize the system and pin point the leak if there is one. As for running straight R-12 and paying $50+ a can, there are alternatives. You can use Freeze 12 which is 80% R-134a and 20% HCFC-142b. It's usually under $10 a can and is a great alternative to use in a R-12 system. If you want to run R-134 you should change the style of compressor and condenser. R-134 usually doesn't work well in a system made for R-12 I've found. Ive run a Sanden style rotary compressor and 134 with good results.