A/C Compressor Won't Kick On

There should be a low pressre switch somewhere in your system that would keep the compressor from turning on if there is no refrigerant in the lines. I don't think the vacuum lines have anything to do with the compressor turning on, they are more for control of the dampers/heater valve. The low pressure switch should be mounted on the dryer or in the line from the evaporator to the compressor. At least this is what I am familiar with from older mopars.