I owe an apology here. I mixed up some threads and thought that it was in this thread that it was suggested that R12 be MIXED.
I get in too big of a hurry sometimes.
I would like to comment on flushing. There is no need for the use of flushing agents unless there has been a compressor failure, or you are converting to a different refrigerant or oil type.
I'm now having to think about a/c stuff, which I'm not accustomed to this time of year.
What you need to do, sms, is put a set of gauges on the system and measure static pressure. If the static pressure is below about 82 pounds, then it is indeed empty of refrigerant and you can proceed toward looking for a major leak and see if the compressor turns free and makes pressure.
If the static pressure is 82 or thereabouts, then it has some refrigerant remaining and you may be looking at a fuse or control problem of some sort. In this case you can still have a bad compressor, but keep in mind that the failure of the compressor is more often a shaft seal leak, than a failed compressor itself.
There is no need to short anything to charge the system if it is just low on refrigerant. The static refrigerant charge will bring the pressure up so that the low pressure protection switch is actuated so you can finish charging with the system running.
The only need to jump the low pressure switch is to see if the compressor clutch will indeed engage. You should do this before turning the compressor by hand to ensure that it is free.
Best of luck,