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Air Compressor Motor Problem

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  • Air Compressor Motor Problem

    I have a Craftsman 1.5 HP Air Compressor that has just recently started to kick out my 20 Amp circuit breaker. Things I have tried so far: removed the belt, disassembled and cleaned the motor, checked all the electrical connections. The motor with no load (drive belt disconnected) will start, run for about 1 to 2 minutes, get somewhat hot and then kick out the circuit breaker. Is it time for a new motor?

  • #2
    Re: Air Compressor Motor Problem

    You're tripping a 20A breaker with no load on the motor? If you have an amp meter and are comfortable using it in a live panel, test the amp draw on the motor to be sure it's not the breaker that is the problem. If it's drawing more than the rated amperage on the motor it's time to replace it. You're not using an extension cord are you?
    Last edited by killavolt; 06-21-2009, 06:19 PM. Reason: Additional question


    • #3
      Re: Air Compressor Motor Problem

      Thanks for your reply Killavolt. Yes, I am tripping a 20A breaker with no load on the motor. I don't have an amp meter but am considering purchasing one. I am not using an extension cord and using the same circuit I have been using for years. Today I moved the compressor to a different location in my workshop that uses a different circuit breaker. Again after about 2 minutes running under no load it kicked that one out to. It starts up normally, without any noise other than a slight humming noise, gets a little hot then kicks the circuit breaker and stops. If I reset the circuit breaker and try to start it again right away, it just kicks it out again. If I wait for it to cool down (about 1 hour), it will run again but kicks out after about 2 minutes. I am pretty sure it is the motor but don't want to purchase a new one because of the cost is about the same if not more than buying a new compressor. It's a shame that because of a bad motor I have to scrap a perfectly good compressor.


      • #4
        Re: Air Compressor Motor Problem

        You might take just the motor to a motor rebuilding-rewinding shop if you have one in your area and have them check it over. It may be a bad running capacitor (if your motor has one) which is an easy and low cost fix. It may be a ball bearing has lost grease and is binding up. If a bearing is bad the motor shaft will be rather hard to rotate once the bearing has heated up. Also once run and hot it will normally make a Z Z Z Z Z sound. Just before the circuit breaker trips and with belt(s) removed does the motor growl louder than normal? Does it make any sounds which are different than when cold started and running?

        This motor has both a starting and a running capacitor. You can see both of them.

        This motor only has a starting capacitor and if bad it wouldn't start up or would be hard starting.

        Please don't use these as examples for your air compressor. You would need to properly match up a replacement motor.
        Last edited by Woussko; 06-22-2009, 03:50 PM.


        • #5
          Re: Air Compressor Motor Problem

          Thanks Woussko for your reply. Motor does not bind up when hot; in fact after it kicks out the circuit breaker it continues to spin for at least 15 seconds. Not familiar with a running capacitor but I think my motor has one. I went to the websites you referenced and mine looks like the one shown with the two capacitors. I understand what a starting capacitor does, but what does the running capacitor do? If bad, could this be why my motor is heating up and kicking the circuit breaker out? Is this an easy fix that I could do myself? Where can I get the running capacitor? I don't think the motor is growling louder than normal. Thanks for those websites and your help.


          • #6
            Re: Air Compressor Motor Problem

            A running capacitor alters the waveform and results in higher efficiency for the motor. If it has gone bad the motor can draw too much current and also bog down when under load. It's a pretty easy fix if you're handy with doing simple electrical work. Normally they have two wires that connect via slide-on/off quick connectors.

            A) Be sure the power cord is unplugged.

            B) Remove both covers and look at the capacitors. Please post any info marked on them and then I can tell you which is which. You need to somehow mark the motor so you know which one is which. Please do this before disconnecting anything.

            A good major (not small) appliance repair parts dealer may have them. Your best bet normally is an electric motor rebuilding shop. If you have or know someone with an account at WW Grainger (Wholesale sales only) they have loads of them with different specifications. You don't need an exact match but you must be close.

            If you are in Newton, NC as per your profile you may want to call up these two places that I found in an online yellow pages directory.

            B & M Electric Motor Service Inc - 20 17th Street Pl NW - Hickory, NC 28601 Phone: (828) 267-0829

            and also

            Industrial Motor Rewinding Co. (no address but claims to be in the area) Phone: (828) 324-9932
            Last edited by Woussko; 06-24-2009, 12:36 PM.


            • #7
              Re: Air Compressor Motor Problem

              if it were me i would take woussko advice. take it to the motor shop. if nothing else call & get a price to check out the motor. + change the capacitor. breid


              • #8
                Re: Air Compressor Motor Problem

                Thanks for your reply!
                I have removed the capacitors and after 23 years of service they look like new.

                The one I assume is the run capacitor has the following information on it:
                B6-16 828 DIELEKTROL GE NO PCB'S CAPACITOR ASSM IN MEXICO Z97F5050 15UF 370VAC 60HZ PROTECTED P965 P10000 AFC D68798-4 A2747-14

                The other one that I assume is the start capacitor says the following:
                MEPCO/ELECTRA 3535B6A0460A110B1 K-8792824AF23 460-552MFD 110VAC 60HZ 3628616 FOR MOTOR STARTING MADE IN USA

                Is there any way I can test the running capacitor? I wonder if one of the places you referenced could check out the capacitor if I took it in to them. The symptoms (drawing too much current and bogging down when under load) that you reference in your reply sure sound like it is the problem but I hate to spend the money on a new one only to find out that it wasn’t the running capacitor.
                I found this on on Ebay (Search Item number: 260274775488), is this what I need?
                Thanks again for your help!


                • #9
                  Re: Air Compressor Motor Problem

                  The first one is the running capacitor. As for testing it, a really good motor repair shop might be able to do it. The good part is they aren't a costly part so if you did just replace it you won't be out that much $$$. I would call up both places and ask if they (A) stock a motor running capacitor of 15 Mfd and 370 Volts. If they do, I would take the old one along and try to get a replacement. You might as well take the whole motor with you. I think they would be able to try it out and swap the capacitor if they think it is bad.

                  Does your's look like the one in the picture below?

                  Please see these web sites:

                  Attached Files


                  • #10
                    Re: Air Compressor Motor Problem

                    The one on eBay sure seems to be electrically the same. I've seen this before where some are in cylinder cans and other are in oval cans. This is where you need to try to match up what you have.

                    If you need an oval one the same seller on eBay has this one listed.

                    One quick check you can do at home is to give the motor the SNIFF test. Does it have a nasty burnt smell?

                    Do you have a VOM multimeter such as a Simpson 260, Triplett 630 or such? If yes you can give your capacitor a crude test, but to properly check one takes special test instruments and they don't come cheap.
                    Last edited by Woussko; 06-24-2009, 12:34 PM.


                    • #11
                      Re: Air Compressor Motor Problem

                      you could take the caps to the motor shop and have them test them. lol. breid