I'm considering getting an extra portable AC on wheels for the bedroom
(which is upstairs) in case my 20 year old central AC were to suddenly die.
That way, I'd be able to get some sleep at night if I weren't able to
immediately have a new central AC installed or the existing system couldn't
be immediately repaired. Is this a good idea or do you I am crazy to want
to spend a few hundred dollars on something to use as a backup for the
bedroom in case the central AC should fail?

Granted my bedroom has ceiling fan, but I'm afraid that alone won't be
enough, because it will most likely be upper 80s or hotter in the upstairs
bedroom at night should the central AC fail in summer.

When central AC is working normally, as an added benefit, I suppose the
portable may also be useful for purpose of cooling the bedroom at night by a
few degrees without my having to lower the thermostat for the entire house.

I already have a portable AC for the home office (also upstairs), since that
room has a cooling problem. I realize the portables on wheels don't work as
well as window units due to negative pressure, but at night when the outside
temperature is cooler they generally work well. Window units can't be
installed here though.

J.