My girlfriend has a 91 Silverado that has a problem getting air to the vents. If you remove the inside of the glovebox, there is a hose or box that is to the right of what I believe is the underdash vent. It broke a long time ago and was sealed with duct tape. I want to replace this part but don't know what is called. It appears to connect two parts - the underdash vent (I believe) and not sure what is on the other side.

I know the description is vague but I am at work at the moment and unable to give a better description.