Heater Won't Blow On The Feet

[livecdtrader]

Good morning. This is my first post. I have a 2006 Pontiac Montana SV6 and we love this vehicle.

Recently, I noticed that the heater blower will not blow down on the feet. The defrost settings work fine. The dash blower vents work fine. However, if I change the setting to anything that involves blowing heat on the feet, I get defrost settings (i.e., the air is blowing out of the defrost vents).

Is there a valve or something that could be sticking? Or a resistor block/relay that requires replacing?

Any ideas would be greatly appreciated.

Thank you!