Dual climate issue
 

Last year, I kept hearing grinding noise behind or under dash. I'm guessing it's the gear to switch or control the heat or A/C from left/right/center. The noise is gone but now heat or A/C only blows out the right side. Airflow is great on Driver's and Passenger side but Driver's side only blows air, no heat or A/C. What could it be and is it a simple fix? Someone told me I'd have to tear the whole dash apart.

Any advice is greatly appreciated.