'96 vent control problem

I have a '96 S-10 with a 4 cylinder engine. The problem is the vent control.
The air can be directed to come out of the lower vents, floor heating, or the defrost vents, but no air will come out of the dash vents. Is this a common problem that can be fixed easily, or are we talking taking the dash apart ?
Anybody else have this problem and what have you don'e about it ?

Mine uses vacuum lines to diaframs that move dorrs redirecting air.

Check all vac lines under hood and under behind dash. Easy to remove panels of lower dash area.

Probably the diafram for vent redirection is broken or door is jammed.

I was thinking about that. I don't think the door is jammed, it will direct the air to all other parts, I will have to start checking the vacuum line for that particular position.