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.

Anyone else have any tips?

Thanks!