The 5 hp electrical motor that drives the pump for my SPA will not start on low speed. When turned on it hums. I hit the Jet switch and the pump/motor comes on at high speed. I can then hit the Jet switch again and the pump/motor will run on low speed. When the set temperature is reached, the pump/motor shuts off. When the temperature drops, the pump/motor tries to turn on but only hums.

I have replaced the start capacitor and still have the same problem.
Where can I get an explanation of what mechanisims are involved that might be preventing the motor from starting at low speed?

Flickit

...solved the motor problem, repost your question in one of the electrical forums.

labman

Likely somewhere there is a good explanation on the net. Unless you are much better than me at selecting search criteria, you may never find it. I have found some motors have a centrifugal operated switch in them that shifts out of start mode once they are going. If they fail to spring back when the motor stops, they will hum instead of start. I have not managed to fix one.

Gayle Quebedeaux

That is exactly what I discovered. The centrifical switch was stuck in the open position. I oiled it and got it working.