ac/heater fan sometimes doesn't work (2001 Honda Civic)

I have a 2001 Honda Civic. A few months ago the ac/heater
fan stopped working. Then an hour or so later, it stared
working again. Last week it stopped working for three days.
Then it just started to work again before I got it to
service.

What could cause this? Not a fuse apparently. It almost
behaves like the car computer decides it shouldn't run
for a period of time, then allows it again. But I don't
think the computer can control it? Can it? Other
possibilities I can think of are: loose wire connection,
failing fan motor (but it seems to behave normally and
with no noises when it works).

Any ideas what this could be?

Thanks.
P.S. I have noticed that the rear window defroster stopped
working some months ago (at least). It isn't intermittent as
far as I can tell. The light comes on on the dash button, and
goes out the proper number of minutes later, but to no effect.
I may have hit a wire in the trunk when carrying recycling,
but am not sure if those wires are easily hit in the trunk.
I think this problem is separate from that above, but
mention it for completeness.