I really would like to know more about this person's expertise, if any.
auto and RV ac units CAN exhaust and take in (fresh air exchange) outside air.
BUT, if the damper is closed, the ac unit draws in air from inside the
vehicle/trailer, runs it over the coil and then blows it back out.
NO outside air is pulled in and you certainly do not want to add an outside air
hole to your trailer.!! You do NOT want to be cooling outside mid day desert
air when you should only be cooling the air inside the trailer. Any outside air
that does get in thru leaking vents, etc is acceptable because it keeps you from
getting sick. from eveything from Legionnaire's to CO poisoning.
I would urge you to think about what some of the people - not only on this elist
but any elist - are saying and then apply some common sense. Along with that,
go to your local dealership (Ford is fine) and ask the AC guy about how the AC
works. you will quickly find out that the only fresh air vent you need is the
one the AC unit comes with. further, that inside cooling or the MAX cooling
setting, is only recirculating the air inside the vehicle.
enuff
chas