When the system gets too low, the low pressure switch make the compressor stop. On the older 850 there is a2 wire switch on the low pressure a/c pipe up by where it goes into or out of the fire wall to the evaporator. disconnect this swithc and jump the switch electrically. Use some thing that has insulation. I used a heavy duty paperclip that I put electrical tape in in the middle and bent it so the two ends could be pushed into the female conection. The compressor should start and you can then add the freon.