Your freon level may have dropped to the point where there is not enough pressure in the system to set the switch in the on position. You can hot wire the compressor to ee if it works. Just umplug the wire going to the compressor and jump it to the + battery. With engine off, you should hear the clutch click in. You can also try it with engine going, but watch for wires and body parts. If the compressor and clutch works hot wired, there is a good chance you need a can of Freon to set the switch. This is a safety thing so you don't total the cooling system.

dick