The air ducts in my car aren't blowing when I want them to. I have to fiddle with all the nobs to get it to eventually blow. It is a big hassle when my windows are steaming up and I can't see and I'm trying to drive at the same time. Is this a common problem? What can I do? I've taken it to the garage multiple times and replaced a certain part but it's obviously not worked. What should I do now?