Electric Power & Utilities/electric motors


I have a 26 gal. air comp. with a 120 volt/15 amp/60hz/single phase motor that turns extremely slow then trips. I installed  new start and run capacitors and problem still exists. I checked my voltage at 118.9 volts. this unit was manufactured three years ago. It was returned to my store for missing hardware and seems hardly used. could I be looking at a bad motor? any suggestions on troubleshooting will be of great help. thank you.

You can check the internal switch by removing the two leads on the start capacitor, and connecting a analog ohm meter to the leads. If the switch is making up, the needle will swing to zero, or very close, showing continuity in the switch and the winding. If not, then the switch may be damaged, or it could be a loose wire, or in extreme case, a open in the start winding.  

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Charles C. Jones


Let Me help you with your problems with single phase and three phase electric motors. I can tell you how to troubleshoot your motor problems. From simple testing of capacitors, how to test your windings, replacing bearings, and general maintenance. Before we go any further, remember these words of advice: Disconnect the power before you do anything! Please limit your questions to electric motors and there immediate components. I review each question, and if I can answer or help, then I will. If you receive a rejection, it means it is out of my expertise, and just do not have the answer. I'll be waiting for your question.


I have 40 years experience in the repair of electric motors and related equipment. I am a master machinist in the field of motor repair. I was employed with my company for 35 years, but retired in May of 2013. The downside to that is I lost access to a lot of technical data. I will still try to give you the most accurate advice that I can.

Former member EASA

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