I have an issue that I've ignored because I thought it was normal, but the more I think about it, the more it doesn't seem right. I have the manual dual climate control air conditioning system in my truck, and when I have it turned off, it still blows a little through the vents while I'm moving. It isn't "conditioned" air...it's just like the vent, and the faster I go, the harder it blows. Is this normal, or is something not closing off all the way??