99 Grand Prix A/C Problem

I've got a Grand Prix that I use for traveling and it is a 99 and has 120k miles. My A/C and heat only work on the highest blower speed. I m wondering if anyone hasa solution to my problem. I am very mechanically inclined and have a general knowledge of car repair. I also have an idea what the problem is but I don't want to skew any of your opinions. Thank you in advance for your responses. P.S. there is also a clicking noise that the serpantine belt makes and the generator seems to be loose and moving back and forth making the noise while the car is running. Please advise on this as well.