How can I fix my Heat/AC so it works properly?

It's been almost a year since it was replaced. I didn't mind at first because I was use to driving in the summer without A/C, and we haven't really had very many frigid days in the winter here to warrant extensive use of the heat, but, I would still like to try to get this fixed. Before the transmission was replaced, heat worked fine on all settings of the intensity dial(sorry I don't know the actual name of what I'm trying to describe, but, I just don't know a whole lot about cars), not just 5 like now. A/C never worked and would never come on no matter how much I pressed the button for it originally. Now, it seems like it's stuck on though it's not really blowing out any cold air even when I set the temperature to the coldest setting(more than likely a coolant problem in this case, but, still doesn't really explain why I can't actually shut it off the right way so the light above the switch goes out).