Mine always blows through the floor and defroster at any temperature/setting except for the actual defrost then it only blows through the defrost.
That is why I just figured it is a vacuum line because I know that on almost all cars if that happens it is due to a vacuum line being cracked,broken, etc. On the buick I had there was one line with a hole in it. I cut out the broken part and slipped on a slightly larger rubber line to connect the to and viola all was well.
Only on this motor almost all the vac lines are under the intake and I don't feel ambitious enough right now
