My 2003 Blazer's heater only blows air out of the top (face) ducts on the dash board. The only way I can get heat down to my feet, or up to the defroster is to shut the dash ducts off. Even then, only a little bit of air comes through the other ducts, regardless of what I set the fan speed at. It appears the mode change button isn't working, as if being stuck at that one position, even though it rotates through all the positions. It does the same thing in the summer, with the air conditioner. Only air I get is through the dash board ducts.
Thought maybe someone here could explain why, and maybe offer a way to fix it.
Thanks

 

More than likely it is mode door actuator that isn't working. Or possibly the mode door itself is stuck.

 

Thanks,
So, I'll assume my next step is to start taking all the housing apart. Looks relatively accessible. Lots of 1/4" or 5/16" screws.
Hoping for stuck doors.

 

There's a lot of metric in there too.

 

Fixed!! Ended up being one broken vacuum hose and one disconnected hose to the canister on the fender well. Everything works now with .63 cents worth of vacuum hose!
Someone here sent me a note regarding what was going on with their own car, and thought it might help me.
Thank you!!

 

Your lucky day!!

 

Yes, oldchevy, it is! Went the whole damn winter with no heat at my feet and no defrosters. Today it got up to around 50 degrees so I started looking around at the vacuum hoses. Found the short broken one and one just dangling out in space.
Now, if I can find out what's wrong with my 4 wheel drive vacuum issue, I'll be in good shape.