first things first, check to make sure the compressor is at least running, ie no belt problems and you should see the clutch engaging on the pulley, and the thing is the way to really be checking is to be feeling some of the lines, certain ones will feel cold certain hot, theres the compressor, evap, a metering device of some kind and theres really no way to just say the a/c is out and something in particular is bad, like there could be frost on a liquid line maybe or is the condenser sweating theres a lot of various conditions
the refridgerant is R134a and dont buy those **** little cans from wal-mart or k-mart or something, actually take it in for a proper evac and recharge unless you know someone with a recovery machine but i really think it needs to head to a reputable shop for further and proper diagnosis.