2000 Impala vent won't switch from floor

2000 Impala 3.8 Automatic

vent inside won't switch from floor to front or defrost. blower speed control seems to be working fine. Would this be a vacuum problem or is the switching done by an electrical control? If vacuum where would be a good place to start? Do I need to pull the control unit from the dash? Any help is appreciated.

thanks

you need a new blend motor