Troubleshooting for air conditioner to work properly

How to repair the air conditioner in a 2000 Oldsmobile Alero. I have tried the dye and sealer then the 134 freon and I had it working for about 2hours max. But next morning back to same hot air. Why can't I see any leaks and why didn't the sealer stuff do it's part? The gage said it was charged in the blue area like it's said it would be to be a complete charge. I am a women mind you, and I like to think of myself as smart enough that I will listen to reasoning. I don't just normally jump into something with out having some kind of knowledge from someone or some where I trust. I'm afraid this time I have been misinformed. : (
I'm out of 80 bucks and I'm still sweating bullets! Please help me if you can. I don't want to be taken by another Mechanic when he sees another female looking as dumbfounded as I do today.