Need help with check valve on hvac
 

I am in the middle of replacing my hvac vacuum lines and i ran into a problem. My vacuum check valve was cracked in half and one of the small nipples is broken off and gone. I have ran a new vac line from the manifold to the new check valve. I see the canister and that plugs into the side nipple on the valve but i dont know where the small other line goes. I believe it goes into the cabin somewhere but where?

Thanks for the help!