To test the switch, turn the a/c off, unplug the connections to the switch and attach an ohmmeter to the connections on the switch. The ohmmeter should read that the connection is open. Turn the a/c on high and the switch should close after a little bit and the fan should come on. If the switch closes and your fan still is not coming on after you reconnect it, the problem is between the switch and the fan. Unplug the fan motor connection and put 12v dc power to it and the fan should come on. If it doesn't, then most likely the fan motor is bad. If the switch does not close then either the switch is faulty or your refrigerant level is low.
I do not remember if the a/c system has to be emptied in order to replace the switch or not. I don't think so, but perhaps someone else should chime in here.
Either way, if the switch is not closing, you should have the system checked by a qualified technician.