AC Trips breaker after 5 seconds

Old 07-24-13, 10:15 AM
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AC Trips breaker after 5 seconds

My AC unit will trip the circuit break after about 5 seconds when it is turned on, the fan will be coming up to speed and then it trips off. I have opened up the unit and the motor, checked for grounds and free rotation of the fan blade and everything checks out. The capacitor was discharged when i was checking it and that makes me think that thats the problem, its only been a day since my unit has stopped working. I dont know how to check if a capacitor is good with my multi meter, does anyone have any input or suggestions?
Old 07-24-13, 10:26 AM
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Welcome to the forums! Some basics. Is this a window unit or central outside unit? What is the rating of the breaker that trips. What is the amperage rating on the air conditioner. Often it is a bad breaker, but we need to cover some bases first.
Old 07-24-13, 02:43 PM
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it is cheaper to buy a $20 capacitor than to buy a meter that will check capacitance.
Old 07-24-13, 07:42 PM
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cap check

if you have an analog meter or a digital meter with an analog bar in it, you can discharge the cap, place it on R X 10,oooo ohms and the needle should go to one side and drop down quickly to the other side of the meter. The second check is to see if its grounded to its own shell in the case of a metal cap. 25 years ago I use to test mine with a RadioShack meter like works fine, it just won't tell you what the MFD is....your goal is to see if it just works and is not shorted out. but just replacing it is a good start either way if you need a new motor you also need a new cap anyway... Hopefully its the same cap.
Old 07-24-13, 07:53 PM
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I just had to replace a start capacitor on an electric motor... it was only spinning slowly (or not at all) and was throwing the breaker. My old capacitor had a thin plastic cover on the end between the contacts, that had a small burn hole in it. In my case, that indicated a bad capacitor... and replacing it fixed the startup problem. My start capacitor was $4.99 with free shipping online.
Old 07-25-13, 03:01 PM
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We generally have two types of capacitors in HVACR...Run caps and start caps. Start caps are more complicated as they are only temporarily in the circuit till 75% of the motors rotational speed is achieved and then a relay takes it out of the circuit. The run cap is metal to dissipate the heat (generally under 88MFD) these do however, stay in the circuit all the time the motor, or compressor, is powered up. Some compressors have both. These are called CSCR, with only the run cap=PSC, with only a start cap is a CSIR and then burners classically have the split phase motor. Then there is a shaded pole motor which is for very small motors with little cost or starting torque.... Torque is the name of the game, once they get to speed, they usually don't need a whole lot to stay there.

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