That gear drive actuator you replaced controls hot to cold blend.
There is a vacuum switch behind the glove box that sends vacuum to separate vacuum doors to control what vent the air comes from.
That black plastic vacuum line that powers the vacuum doors goes through the fire wall between the master cylinder and the strut tower.
This is what the vacuum door controller looks like.
https://www.rockauto.com/en/moreinfo.php?pk=14268801&cc=1021374&pt=7036&jsn=531