My air in general only blows out through my defroster vents. I own a 91 laredo 4 liter. My Heater Gage's are sliders. The blower works fine but I can get air heat or vent air through my heater (feet) or the central and side vents. What do you think what is going on.

 

Blend door stuck/not getting vacuum. Check vacuum line from heater to vacuum reservoir canister behind the front bumper. Most likely broken/disconnected somewhere.
That will get you started.
Search the forum and you'll find this is a common prob. Lots O Info posted 'bout it.

 

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