look for a pressure sensor somewhere on the low side, might be in the accumulator even, it will have 2 wires, unplug it, start the vehicle with the A/C turned on, and jump the 2 wires in the plug, see if the compressor fires up, if yes, make sure you now have a full charge, as you might not have gotten a full charge with the compressor not running, if it runs, and it has a full charge, you need a new low pressure switch