Hey guys I'm new here, I have an 03' FX4 Lariat. 5.4 L .I have a vacuum leak problem making the ac blow out the defrost. I'm going to try changing the o rings on the ATEC . But first can anyone tell me about this black vacuum line not connected to anything . It runs along with a blue and tan line on the left side of the firewall. The blue and Tan are each connected to something that is electric and vacuum controlled . The black one is just hanging there. Does it connect to anything. I searched for an hour and found nothing .I've pulled the battery out and checked behind there and everything is fine. Thanks guys for your help.

 

I'm fixed, it was the o rings in the auto air controller. Thanks to Devilsrighthand aka Mike for posting a rebuild thread. It looks like an extra black line was run against the firewall . Go figure