2012 Chevy Sonic is not switching air vents when I change the designator switch

What is your question?

The fan is blowing hard, but I don't get air especially to the defrost vents when I switch it to defrost mode, etc... The air cabin filter is new and not clogged. Even when I change the air from outside to inside, there's no difference in the amount of air being blown. It seems like it's just locked in one mode which definitely isn't defrost mode since my front window continues to fog up. I'm pretty car savvy and it's not anything I'm doing wrong or not understanding with the different air modes, etc... The air does heat up well, just nothing to certain vents. Bottom line, I can't keep my windows defrosted which isn't good! I'm hearing it could be a air door/gear problem. Thanks for any help.

What makes this problem better or worse?

When it's cold outside, trying to defrost the windows