Vacuum switch problem

[Jlbloom40]

I own a 97 Taurus wagon 3.0 24v . My selector switch for panel floor ac defroster does not seem to work correctly it is stuck on defroster. I pulled the vacuum harness off the switch and could not feel any kind of vacuum. My question is which line is the source because they are color coated and where does it go. Ive looked on here but could not find it maybe not the right key words.Thank you for your help

[Airjer_]

There is a vacuum line that runs through the firewall that supplies vacuum to the switch. The problem is likely under the hood.

Vacuum controlled HVAC default to defrost when there is no vaccuum as a safety feature to keep the windshield clear