My son, a mechanic for 30 years, says that Freeze 12 is totally compatible with R12, and works just as good. I still have about 6 lbs. of R12 so haven't tried it yet. I did switch my Jeep from R12 to R134, and as said earlier, it's barely half as good. My son said that if they don't change the compressor oil (which many don't) it will be worse yet. Only remedy is to flush, reservice with the proper oil, and use the corresponding freon.