Well found this post on another forum:
May invest $25 in a Harbor Freight scope!!

08-14-2022, 12:08 PM #
11 kenandterry
Kanadian Kamper
Join Date: Sep 2010
Location: Southern Ontario
Posts: 6,726
Got it fixed!
Sorry to everyone……I forgot I’d posted this trouble.
To summarize, in discussions with a Ford service expert (for a minimal fee) it was determined that in order to really gain access to the entire dashboard air plenum, you have to remove the steering wheel, gear selector column cover and piece by piece, the entire dash unit from door to door and windshield to floor.
I was not about to tackle this in the middle of camping season.
With the help of an endoscope camera, numerous extendable coat hangers and such, then using an air compressor nozzle, along with an industrial shop vac, I cleared a whole lot of pink insulation and dirt that were clogging my side of the plenum…..thanks to some critter….squirrel, chipmunk, or whatever.
I spent several days at it, until virtually nothing more would exit the vents anywhere.
Good powerful air ventilation, with or without air conditioning.
Done, and so glad it works as designed. My next project, try to figure how to block future critter activity.
__________________

Ken and Terry
2018 Sunseeker 2430S-CD, nicely modified and carried by a 2017 Ford E450 Sport
Former Georgetown 330TS owner for 10 years with more mods than I can count