I am looking at buying a 2003 Silverado HD 4x4 and it has a clicking sound coming from the drivers side dash when the air is on only. It does not do it all o f the time. It sounds like maybe a servo clicking when it is trying to open and close. Has anyone had this problem?

 

I have a 94 and it is doing the same thing. It does it when I turn it on Max A/C.
So I think that it has something to do with switching the air flow from outside air to the recirculation air in the cab. So I dont know if it is a vaccum problem or something electrical. On top of that the blower motor seems to work when it wants to. I dunno either. I just registered on to this site hopefully someone knows about resolving this problem.