HAVC question

I somehow broke one of the stock plastic vacuum lines that goes to the havc and its now completely missing. I want to replace it with a rubber hose but not sure where it went to. I have the tee capped off where it starts near the fuse box but where does it go to? Does it go through the firewall to the blower motor? Want to get this fixed as no matter what setting I'm on whether be the floor/defrost or head, it blows out all locations.