Spa/hot tub A/C pump hums, but does not run

Question

When I turn on the power to my hot tub at the breaker, I can hear the relays closing and the pump hums for a short while, but it doesn't turn.

I recently drained and filled my hot tub. After refilling, I ran the pump for a few minutes to circulate some chemicals, so it was working at the time. I then turned off the power at the breaker to check something. Then, when I turned the power back on, the pump wouldn't start. The control panel lights up. I can hear the relays click in the control box, and hear a humming for a few seconds (the pump trying to start, maybe, it's hard to tell) then the humming stops.

I read that air in the pump can prevent priming. However, the pump did run for a few minutes after we refilled the hot tub, so I don't think it's air in the line. Just to be sure I loosened the outlet connector on the pump and water drained out, in hopes that any air would be released

The control box unit has two fuses labeled pump 1 and pump 2, and I've checked and they're both good.

The pump connects to the control box via a specialized plug, and I'm sure it's well connected.

• Maybe the capacitor on the pump went out? As I indicated, it's probably 10 years old. How do you troubleshoot that?
• Something jamming the pump from turning? How can you check that?
• Anything else?

Update 1 Replaced the capacitor and it ran for a short while but stopped again. I've removed the pump and will test it on a bench.

Update 2 After pulling the motor out I confirmed that the impeller could be easily turned by hand, so it wasn't jammed.

Answer 1

After pulling the motor out (which required draining the spa and disconnecting the PVC connections) and removing the cover, I found another capacitor. Googling the part number indicates that this is a start capacitor. It helps the motor start.

The motor also has a capacitor on the outside, and it's the run capacitor. That's the one that was replaced first.

After replacing the start capacitor, the motor started and is running.

http://en.wikipedia.org/wiki/Motor_capacitor

It turns out that Spa/hot rub AC motors like this have both a start and run capacitor, as do blowers on forced air furnaces and air conditioning units. If an AC motor like this won't start, there's a good chance it's the start capacitor. The start capacitors tend to fail eventually, the run capacitors last much longer, apparently.

My spa motor

Start capacitor

Run capacitor

Answer 2

I think the answer comes in one of the three things you've already stated: 1) bad pump motor; 2) capacitor; 3) impeller jammed.

In your case I believe the problem is with the motor (as you've probably already figured out).

• You've already replaced the capacitor. If this were truly the problem, it would have fixed it more than allowing to run for just a moment or two (obviously).
• If the impeller was jammed with something, changing the capacitor would have had absolutely no effect on it.
• The description you provided sounds exactly like what an electric motor does when it's going out ... it stalls with a hum.