My 1996 MAXIMA Air Conditioner is HOT!!!!!!!?

added freon, worked three days, took it to the dealer, they said compressor, leaks, etc, are o.k. anybody out there who has this car ('96 Nissan Maxima) ever had this problem? if so howd you cure the prob for good. btw, i keep this car in EXCELLENT concition, when brakes need replacing, i take it for reparing, prompt oil changes, i dont mess around on this car because im not paying another car note. i would like some idea for the purpose of preventive maintanence. thanks ya'll.