05 Chevy Trailblazer AC?

[Kicker]

I was wondering what would make my air coming out of my vents shut off when it wants too? I have only used the AC so far. I haven't had a chance to try it on the heater. It worked fine for almost the whole year I have had it. It just started this a few days ago. If it doesn't come on when I crank my truck I can hit the dash with my hand and it comes on. Please Help thanks in advance

[jadamgrd]

You mean the fan switch?
Let me ask a silly question... This vehicle ever been under water?
I had this happen on a dodge PU and the plug contacts at the firewall was corroded.
Electrician told me it was common for vehicles that had been submerged. as I had suspected mine had been before I bought it several months earlier