Once upon a time I was member of the Merdcedes Benz Club of America. During that time, I recieved information on how to convert from 12 to 134. If I still had access to this procedure I would send it to you. My recollection as to the most significant issue with conversion is refrigerant oil compatibility. Depending upon who you believe, there is now an oil which is compatible with both refrigerants. As for me, I had 2 cans of 12 squirrelled away. When that runs out, I will have to convert.