Vacuum line

I trying to resolve a no heat but overheating issue I found a lone vacuum line coming out of the passenger side firewall about directly behind the glove box. It runs up beside the washer reservoir but then it stops. I figure there was a rubber elbow/splicer that connected it to what ever. That's my problem, I can see anywhere or another line that it would be connected to? I've tried to pull up diagrams but haven't found it yet. Anyone have any ideas? And could the actuator that controls the cold air hot air be bad cause it to overheat?