You can jump the connections from the low pressure cutoff switch on the reciever/dryer and see if the compressor runs. Just connect for a second to see if it causes the clutch to engage and starts running. If that happens maybe you are just low on freon.

If it is low you might want to add dye and freon and see how long it lasts. If it only lasts a week or two you may have a good size leak that you'll need to locate.