While looking at my vacuum lines yesterday to try and see why all my selectors work except defrost I found a port in the engine bay. Towards the bottom of the battery tray a little port come thru the firewall and was blowing cold air while I had the AC on. What is this for, it is suppose to be open or plugged? New to jeep but never noticed something like this on other jeeps. It's about an inch long, rubber port or nipple.