According to Squanklin :
I have a window AC unit in an upstairs bedroom that is not putting out
as much cold air as it once did.

Normally the unit runs all day and night, set at a specific temperature
(77 degrees, currently); and the compressor kicks in as needed to
maintain that temp. Because the air flow seems a bit lighter and not
as cool, I wonder if something might be wrong with the unit, or if
perhaps it has 'frozen' and needs to thaw. It's about three stories
up, so I can't get a good look at it from the outside, but I see no
evidence of ice or dripping.

In case this is the problem, I have turned it off for the day.

If the unit has frozen, it won't be visible from the outside.

If the unit has frozen, ice will probably be visible on the
coils/fins on the front of the unit once you pull off the front panel
and look underneath the foam filter. The foam filter may be frozen to
the fins, so, be careful not to tear it.

If you don't see any evidence of dripping (presuming high humidity),
you may have a much more serious problem with it. But rule out
plugged filters (soak/wring/hang dry the foam filter)/freezing up first.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.