After initial fill, Speedaire motor just hums

by Anthony LaGrasta
(Mission Viejo, CA)

Great site, thank you!


After my small Speedaire unit fills, it shuts off correctly. After some use, it tries to fill up again, but only results in a hum.

Without the belt attached, it runs fine.

I replaced the start capacitor, but no change.

I do not believe this unit has an unloader valve.

Could it be the power cord has deteriorated and once warm from the initial fill up, causes too much resistance to power up the motor again?

Once cool, it starts and runs again.

Comments for After initial fill, Speedaire motor just hums

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Mar 06, 2015
Yes... but - did you check the unloader?
by: Bill

Anthony, pulling the compressor pump apart is a fine way to spend some time if you enjoy that sort of thing.

If you are doing that, I would suggest that you have a gasket kit for the pump on hand for when you reassemble it.

And / or, if you feel it's the valves, might as well have a valve kit handy too.

But if you haven't checked to be sure the unloader valve is working, and if it turns out that it is not, then that is likely the problem.

B.

Mar 06, 2015
opening the pump
by: Anthony

After more poking around, it seems the valve is fine. It starts and stops at appropriate psi. And the motor turns fine if the belt is removed.
The actual problem is it won't turn over the pump after an initial fill. The switch ask for the refill and the motor starts to try turning. It seems the pump is the problem. I think I'll open it up…

Mar 03, 2015
Test unloader
by: Bill

The unloader valve works when the compressor stops running.

Please see the pages on this site about the unloader valve for a complete understanding of what it is and what it does.

B.

Mar 03, 2015
valve test how to.
by: Anonymous

how to test the valve you mention?

Feb 27, 2015
Found it
by: Bill

Saw some images of your air compressor model 3Z394 on line, and though they weren't that clear, it appears as though the compressor has a pressure switch, and I believe the unloader valve will be part of that switch.

You need to determine if the unloader valve is working first. Then, if so, we can talk about next steps.

Bill

Feb 27, 2015
model and serial
by: Anonymous

3Z394
12296-966206

Feb 25, 2015
Hums on restart
by: Bill

It's humming as it's trying to start and cannot, Anthony.

Not knowing the model I can't determine if it has an external unloader or not, but I assure you, it has an unloader of some kind, and it sounds, since you replaced the start cap, that the unloader is not doing it's job.

Or, with the power off and the tank empty, remove the tank check valve and make sure it's working as if it will not open properly on the refill (there is still air in the tank) that would back pressure the pump and increase the load on the motor.

Make sure you are not using an extension cord.

Bill

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