Chevrolet Repair: Heat Air Flow To The Floor, chevy blazer, vacuum problem

Question
I own a 1999 Chevy Blazer 4 door, when it comes to my AC/Heat, I have three controls/knobs on my dash, one for the fan, second for the temp, and the third control controls the AC/Heat, front windsheild defrost vent, dash vents and the floor vent. I had the 3rd control replaced about two years ago from the dealer where I bought the vehichle, because it constantly blew out hot air even when off, during the summer.

Now My problem is, everything works fine except the heat will not go to the floor vent, even when you put it on that selection it usually blows out the dash. Is this a control problem, or a relay problem OR is it a vacume hose problem? I have been told all of those from different people. And the repair manual I have is very vague. Thanks.

Answer
Hello Anna,
The only relay I know of is the blower motor relay, and the a/c compressor relay. Neither would have anything to do with air flow.
I think it is a vacuum problem, and could be the controller, a hose cracked or off, or the vacuum actuator itself, or something could be blocking the door from shifting, like a pencil dropped down the defroster vent, etc.
Run the engine for a minute or so, then shut it off, and listen closely as you select different air delivery options. If you hear a steady vacuum hiss, track it down.

Van