Check the AC & HVAC fuse first. The compressor fuse too. Then, is it low on refrigerant? Put some 134a in it if it needs some. That's usually the main reason AC doesn't work. It won't come on if it's too low on refrigerant. You can stick the can of refrigerant in a pan of hot water and the refrigerant will leep right into the ac system like a trained pet. Maybe put a can in and see what it does. If it get's kind of cold, put in some more. Ideally you would have a buddy with some AC chops check for refrigerant pressure (using gauges) to see if it's low and go from there till it's full. You can overfill too.
Besides refrigerant, there could be 2 dozen+ other reasons why it's not working. If that's the case you might be better off finding a good refrigeration shop that does a thorough analysis, ...not the lowest price place in town.
