Explorer a/c vent not blowing

2002 Explorer with 4.0 V6 and manual a/c. My problem is that the a/c blows through the demister and the foot vents but not the dashboard vents. Is this caused by the blend door? Of so, where is it and how do I get to it?

Thanks for any help.

This truck uses vacuum motors to move the vent flaps. The defrost/foot well position is the default if the system leaks vacuum. It gets vacuum from the engine, and uses a check valve to maintain even vacuum. I’m guessing you have a vacuum leak in the system, anywhere from the engine to the control module.