Charlie Self wrote:

It may only be the capacitor. My knees are acting up, so I hate
climbing the pull-down to check the thing out again, but I guess
tomorrow evening, when it cools down, is a good time. I've got to drop
a jointer at a freight company tomorrow a.m. early, get that off my
back (3 to go!). There may be some fun with the capacitor, as the
furnace is at least 20 years old. Worked when I got it 5 years ago.
With the gear I have now, the best way to check the capacitor is to
get the numbers, buy a new one and try it. I did locate my small
multi-meter a couple days ago, right on the beam running down the
center of the attic, next to the furnace.

Damn, Charlie, you ARE THE MAN! A dedicated multi-meter, just for your
furnace! Wow!g


Anyway, what I get now is a humming noise, which tends to remind me of
a motor with a bad capacitor, but it's been a lot of years since I
fiddled with them, so what do I know. No motor shop here, but maybe one
in Roanoke or L'burg. I do have a nearly new motor out of an old oil
furnace. Wonder if that will fit?

Possible that the problem is the centrifugal starting switch. I have an
intermittent problem with one on a heavy-duty paper shredder at the
office. In my case, I was able to rule out the capacitor (after using
your method, of courseg) by turning the motor by hand a half turn and
then applying power to it. It turned right over. Give your squirrel
cage or fan a spin and then apply power and see what happens.

A shot of electrical contact cleaner and/or blast of compressed air
aimed at the switch may be all you need. If that gets it going again
fine. If it only works to be a temporary cure at least you know you're
not looking at a great expense. A motor repair shop should be able to
take care of relatively cheaply. Of course you still get to work on it
up in that attic. Sucks to be youg

Good Luck.