If you do the charge Flush the system first. there is a flush made for it. Pull a vacum on the system, see if it holds. Then just get a charge kit. 2 big cans of 134A should be enough. Get a nice hot day and charge slowly, when it starts to condensate( drip out of the passenger compartment coil)you will feel cold air out of the vents. Your done. I'm useing a 72 celica system a lot of retro fitting. I'm running the compressor on a 12VDC motor, not the engine. It is a lot of work and a real challange to make every thing fit. Good luck. Most R12 systems will convert.