Heater stuck on defrost?

So I have a 96 Tacoma that is giving me some trouble in the HVAC system. The heat only comes out of the defrost vents. A/c works just fine on whatever setting- floor all the way to defrost.

I have manual controls, I can hear the mixers move, what do you think is going on?

The heat blows plenty hot, just only to defrost. It’s been like this for a couple years, at least it’s defrost but I’d like to fix it all the same

 

Sounds like a blend door actuator. I don't have access to the service manual right now but you might want to get your hands on one and see if there's a diagram that might shine some light on it.