can't change direction of airflow

i can't change the direction of airflow. fan works in all setting and temp changes ok. but can't get the airflow to move from vent setting. is there a troubleshooting steps that i can do, besides just replacing part and hopes it will fix it.

Check for a vacuum leak. Usually these vents change locations by using vacuum you may have a leak that is not allowing the direction door to change. I would start with the control switch.

I would like to thank you for your help. I started at the control and worked my way to the engine compartment. Found a broken vacuum line by the just below the the battery. The line tee'ed there one line came from the vacuum pump and the other connected at the fender and the third went around the battery along the top of the fender to the fire wall. I fixed the broken line and everything work fine now. My wife is so happy now.

Thanks again.