Climate control problem

I am having a strange problem with my 2003 Silverado. When I start the engine, the A/C blows out the front vents and, there is also a noise that sounds like a directional door is repeatedly cycling closed and open. Within a few seconds, the A/C quits blowing out of the front vents and begins blowing out of the vents on top of the dash near the windshield. I am guessing some type of vacuum problem, but I don't know how to trouble shoot this type of problem. Any ideas? I can live with this until the humidity gets too high and water start condensing on the windshield.

I also Have a 2003 Silverado and have the same problem. Glad to know it's not all in my head. If you find out anything let me know would you? And I will do the same.

Thank you for you post Darius6t9. I thought everyone was ignoring me. There is good news - I think we almost have it figured out. My future son-in-law knows a mechanic that understands climate control problems. This guy told me that it was a bad blend door motor. I called my local Chevrolet dealer and ask about a new blend door motor. The parts guy told me that there are three components, one that determines the temp, one that determines the direction out of the dash (Eureka!) and I forget what the other component does. Anyway, he called it a valve. I talked to the mechanic and he seemed to understand. Anyway, I am going to run my truck by the end of this week or the first of the next and let him try to fix it. The part is about $65 dollars from Chevrolet - but I have no idea where it goes or how to get to it (I'm too cheap to buy a good shop manual). I will keep you posted on my progress.

My climate control problem is now fixed. The mechanic was correct. The actuator is not vacuum controlled - it is an electric motor. I purchased a new actuator - the GM part number is 89018374. It cost about $62 from the dealer. I paid the mechanic to install it. It it located under the cover (kick) panel that is below the dash and above and just to the right of the gas pedal. The climate control works great once again!

cool. thanx for the info. now I need to figure out why my A/C runs when I have the recurculation button pushed but not the a/c button and no defrost on.