Sorry. I thought it would be understood that the air under discussion is
the condenser air supply, not the evaporator (inside coil that the cool
air comes out of) air.
On an auto A/C the condenser is the coil in front of the radiator (99% of
installations). It draws air from in front of the condenser and exhausts
it out the back through the engine coolant radiator into the engine
compartment.
On a house A/C the condenser is the coil on the outside of the house,
either in the part sticking out the window or in the unit sitting outside
the house. They draw air usually from the sides and blow it through the
condenser out the back of the condenser.
In the portable roll-around units mentioned, the "outside" condenser is
physically inside the house, but it has to have its air ducted outside.
If it does not have both an intake duct and an exhaust duct, only an
exhaust duct, it will draw its condenser air from the already-cooled air
inside the house. This is highly inefficient, far worse than a furnace
that draws only its combustion air from the interior, as the volume of
air drawn from the interior is much greater for an A/C. (All RV furnaces
I know of draw their combustion air from the outside.)
Most of us do not run the vehicle A/C on recirc except when cooling down
on a hot day or when we're about to run through a cloud of dust or smoke.
Even on recirc all auto front A/C units still pull some air from the
outside - it's a safety feature to keep any exhaust gases from being
drawn into the cabin from the rear. This is just the opposite of house
A/C which is normally recirc only, and on "exhaust" diverts only a small
fraction of the indoors air to the outside, which is of course made up by
infiltration (window and door leaks) air.
"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."
This is the evaporator air, not the condenser air, which was what was
under discussion.
Al G.