Ac trouble on a 1998 explorer

[Ralph28]

I checked the vacuum lines one line was burnt from the manifold . but I can't locate where the line goes . the 2 that goes to the reservoir under the wheel well is in good condition . What is the third line it's grey and black .

 

[david4451]

On my Sport Trac that line goes to heater control valve on the engine underneath the alternator.