Need Help Please...

I haven't really had a problem with my car until now. The other day it started to shake when I turned it on, and continues to shake ONLY while the air conditioner is on. When I turn it off, there is a small amount of shaking but not as bad as when it's on. My car makes a loud like fan noise when I drive, and it's never made this before.
We changed the spark plugs and the spark plug wires, but it didn't help at all.
Any ideas?

Well... 1st off, what kind of sentra/200sx and year do you have? 2nd... i'm not a super mechanic... to tell you the truth I can't even change my own plugs or oil in my car, but I have known people to have this problem before and i'm always willing to throw out some ideas. Is your AC less cold than it used to be? If it is or even if it isn't, your AC compressor might be throwing in the towel. Kinda depends on how old your car is and how much you use your AC... or it could just be a faulty compressor. My advice is if you can't find anyone to verify that out of the people you know or any more input from the outside... take it to a shop.

might have a belt or pulley problem involving your AC, when its on it is very noticable, but even with it not on it would still shake some