by Tom Connell
(United States)

I just bought a Sanborn 3 hp Magna Force compressor. It looks to be rather new.

Sanborn 3 Hp Magna Force Air Compressor
Sanborn 3 Hp Magna Force Air Compressor

When I turn it on it starts pumping but quickly slows way down and quits running before it gets to 30 lbs of pressure.

I took the belt off the motor and turned it on and the motor runs fine. When I put the belt back on the same thing happens again.

Any ideas on what’s going on with this compressor?



3hp sanborn magna force slows way down
by: Bill

Tom, what is the voltage of the motor, and please describe how you are getting power to it. In other words, are you using an extension cord or power bar?


Mine does same thing
by: Gary

My model #112A300-30N. does same thing. You first tun it on it runs fine but after a few seconds it pulls down and then shuts off (before tank is anywhere close to full) I think it may be pressure switch, but I’m no expert.


Not pressure switch
by: Bill

I doubt if it is the pressure switch.

Typically this issue is created by a couple of things. Either the motor cannot overcome the increasing load of a mechanical issue in the pump, or, the motor isn’t getting enough power from the source or through the run capacitor.

That’s why I asked the original poster if they were using an extension cord. Often a too small cord is the reason the motor lugs down when pressure builds.


Check The Voltage Wiring inside the J box on the motor
by: Anonymous

Sounds like the motor could be wired to run on 220V but the has a 120V plug. that would make the motor run as you describe.

check the schematic inside the cover of the Junction box on the motor to make sure it is wired correctly for your electric supply.

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