I have this old 1/3 HP AC Motor attached to a furnace fan that I want to control the speed of. I want to slow it down. I have done a lot of research, but I am not an electronics engineer so I get lost by the terminology and I'm not sure what I have and what I need.

It looks to be a single speed motor from what I can tell, with no built in way to make it run slower. Is this motor brushed or brushless?

Can I control with one of these options?

  1. https://www.amazon.com/Electronic-Controller-Variable-Adjuster-Hydroponics/dp/B07T9BLJ7L
  2. (Harbor Freight version of #1) https://www.harborfreight.com/power-tools/routers-cutout-tools-lathes/router-cutout-bits/speed-controllers/router-variable-speed-control-dial-59386.html
  3. https://www.amazon.com/KB-Electronics-8811007-Variable-K177-1006/dp/B000F9FCQS/
  4. https://www.amazon.com/Controller-Voltage-Regulator-Attemperation-Thermoregulation/dp/B0894LG58M

I see VFD come up often as a recommendation, but my searches turn up expensive options!

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2 Answers 2


I would consider using a different motor. That motor has to come to a minimum speed where the centripetal switch switches out the start winding. If that does not happen it will eventually fry only the motor if you are lucky. This eliminates just about any external VFD (Variable Frequency Drive) option however if it has a pulley you can change that.

  • Good point about too-slow speed setting not letting the centrifugal spin out! Mar 5 at 23:28
  • Good suggestion on the pulley, that option came to mind. I want to make a woodshop air filter and use this furnace fan (connected to the motor) to pull air thru filters. It just seems like its running too fast. Could change the motor pulley to be even smaller.
    – Airn5475
    Mar 6 at 17:29

Based on a web-search "westinghouse "316P759" motor" this appears to be a split-phase AC induction motor with centrifugal-switch starting winding. https://en.wikipedia.org/wiki/Induction_motor

This motor has no brushes in it. It is one speed, no built-in way to reduce speed. It is reversible, per the label instructions.

VFDs appear to be the modern method for speed control for induction motors.

  • Good point! Editing to remove "brushless" reference. Mar 6 at 13:31

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