My only comment is that I have read on this forum that one can bypass the sensor that shuts off the compressor so that you can recharge it yourself.
Don't rely on my comment. Do some research.
Also be aware that sometimes ya need to add lubricant with the freon.
again I am no refrigerant savvy person but if ya have lost alot, you ought to try to make sense of the situation before committing R-12 or whatever you use...but I guess ya already knowd that...
good luck !