I have this same problem. I noticed the a/c would be running and then the air would get warm and i would look down and see that the a/c had turned off. I would jiggle the nob and the a/c would turn back on. I let go of the nob and back off, depending on where that nob sat depended on if the a/c was on or off. I actually did what "Starship" posted here, before i knew anything about it. and guess what, it worked for me. Now i have noticed if the contacts start to get dirty again the nob starts to act up again. but it is simple for me to clean again.
I have had to clean it twice since i started driving that car, oh in about three years of having that car.
