Recently he had cold morning and I noticed that till the cab warms up around 15-45 min I get like buzzing sound comming above my head. When I put my ear to it looks like some kind fan bearing is bad or something mostly I notice is when I shut the truck down when all is off sound like a fan is slowing down... just wondering if it is easy fix or what is it exactly...or how does it work...thanks for the input no warranty on the truck alost 90k

Might help you.

http://dieselplace.com/forum/showthread.php?t=38250&highlight=climate+control+sensor

thanks I guess I have to see how hard it to change it on my driveway....thanks guys

If I were you I'd try the can of compressed air thing first.....