2000 Mountaineer - No air coming out front vents

[slb2014]

Our front air vents on our 2000 Mountaineer have stopped blowing any air (cold or hot) recently. The a/c and heat themselves work fine, and the fan still blows air out in all vents except the front facing vents. The air is still cold, but it now only blows out the front windshield defrost vents and the back seat vent.

It is very strange, and only recently started doing this. I am hoping that someone here has either had this same problem, or has heard of it. I have no idea why it would suddenly stop working, or even how to begin to fix it.

Thanks in advance!