On Wednesday, January 31, 2018 at 12:11:44 PM UTC-5, wrote:
On Tue, 30 Jan 2018 10:24:36 -0800 (PST), "Dave, I can't do that"
wrote:

Hi All,

Subject says it all. We have a 110vac, 1/3hp, 2-speed motor on the swamp.

https://www.homedepot.com/p/2-Speed-...2204/100013540

I would like to have variable speed. Are there any kinds of controllers that will do this without changing motors?

The Low speed is not low enough so I a looking to just use the High speed wire to the motor and spread control over the entire rpm range.

I am looking for a low cost thing. Kinda like a ceiling fan control that handles a 1/2hp motor. I say "1/2hp" for a little wiggle room if I have to change motors at some time in the future.

Possible?

Thanks
If your motor has a switched start winding then you cannot run it a
lower speed. The start winding is disconnected from the power when the
motor reaches about 85% of the rated lowest speed. From the link
provided it looks like the motor has a switched start winding. Turn
off the motor while listening to it and if you hear a click and/or a
whirring sound then that is the switching being heard. The motor will
overheat rapidly if run too slow. For two reasons. First, the start
winding is not made to be energized for more than the time it takes to
start the motor. It heats up rapidly. Second, the motor will draw more
current as the voltage drops in an attempt to get back up to speed.
This extra current draw will cause the windings to run very hot until
they let out the magic smoke.
Eric

Third reason: At reduced speed, there will also be reduced airflow over the windings which will contribute to overheating.