Air in my face

I've read more than a few posts about people who get no air to their feet, but it's all coming out of their defroster. My problem is that I have almost all the air on my manual HVAC system coming out of the dash no matter what the setting is. I can set the HVAC to full defrost; I still get most of it in the face. And there's almost nothing going to the feet as well in the corresponding settings. Even if I shut down all the dash vents, the air still gets forced out around them. If the system (on a 2001 Jimmy SLE 4-dr, if that's significant) defaults to defrost with a lack of vacuum, as some posts on all-defroster problems have suggested, my problem appears to be something different. Or is it? There's also (from other posts) the question of a cheap plastic actuator that forces open the floor vent; but that wouldn't cause the air to skip the defroster in favor of the dash vents, would it? Would love to hear suggestions, especially since I get no suggestions from AllData; thanks to all.

I've read more than a few posts about people who get no air to their feet, but it's all coming out of their defroster. My problem is that I have almost all the air on my manual HVAC system coming out of the dash no matter what the setting is. I can set the HVAC to full defrost; I still get most of it in the face. And there's almost nothing going to the feet as well in the corresponding settings. Even if I shut down all the dash vents, the air still gets forced out around them. If the system (on a 2001 Jimmy SLE 4-dr, if that's significant) defaults to defrost with a lack of vacuum, as some posts on all-defroster problems have suggested, my problem appears to be something different. Or is it? There's also (from other posts) the question of a cheap plastic actuator that forces open the floor vent; but that wouldn't cause the air to skip the defroster in favor of the dash vents, would it? Would love to hear suggestions, especially since I get no suggestions from AllData; thanks to all.

Usually cased by low or no engine vacuum to heater controls.
Check for good full engine vacuum to heater controls.
Check vacuum tank if it has one and all plastic and rubber lines from engine intake to heater controls.

Is it auto AC controls or manual?

As I said in the original post, manual controls. Will check around the vacuum lines, thank you. That brings up something: I don't think I've ever heard the usual vacuum noises when I change the position of the control. I'm sensing a pattern.

The vacuum-operated diaphragm that operates the divertor door probably has a leak. If all you hear is a hissing sound when you try to change the mode, then this is probably what has happened. It takes some doing to get to it, but fortunately the dash can be loosened and pivoted back towards the seats to gain access to it. I think the part cost me about $20 from the dealer. Hope this helps!