95 blazer

One day the air stopped flowing through the front vents, it is now stuck on the floor and window vent. I have checked and replaced the heater controls and vac line from the back and still no air flow. Any ideas? Stuck vacuum actuator?

Thanks for your help!

 

My Blazer did something very similar a couple of days ago. The dash vents and the dash with defrost vents work OK. When I put the control on the floor vents or the floor with defrost vents, it only blows air out of the defrost vents.
The windshield is defrosted, but the feet do get cold this time of year in Vermont.

Anyone have any ideas?