I have a high velocity fan that seems well-made but quit on me last year. When I turn on the switch, I get no movement, no hum ... nothing.

I'd like to think the switch is at fault ... but I notice it has a capacitor labeled 7 pico Farad, 250 VAC (the unit is 120 ... I'm just reporting what's on the capacitor).

Basically, it could be the switch (in which case I'll bypass it and have it run on high whenever it's plugged in), the capacitor (in which case I want to replace the capacitor), or the motor (in which case, I'll through it in the scrap bin).

Should I jam the leads of my multi-meter into the wires coming out of the switch to test? Or ... test the capacitor somehow?


  • 1
    250 VAC rated is what you want on a 120VAC motor. Safety factor is good, otherwise you get a "confetti generator" sometimes with flaming confetti (what started as the guts of the capacitor.) There's possibly also another switch you don't know about, the starting or centrifugal switch - depends if it's a capacitor start or capacitor run motor. – Ecnerwal Jun 24 '17 at 2:23
  • 120volt AC is 120 volt RMS and peaks at 170 volts. Hence the 250 volt rating. – ArchonOSX Jun 24 '17 at 9:17

A capacitor is defined as two conductors separated by a dielectric. Consequently, there is no direct electrical connection between the plates or conductors. Current only flows to charge the plates by pulling electrons out of the dielectric.

So, on a good non-polarized capacitor, connecting your ohmmeter across the capacitor should show low resistance at first and climb to overload as the capacitor charges up to the voltage of the meter and resistance to current flow increases. Reversing your leads will then yield the same result.

A shorted capacitor will show zero resistance either way.

An open capacitor will show infinite resistance either way.


You can check the capacitor with your ohm meter, put one of your leads on the positive and the other lead on the negitive, the meter should show a reading for just a second or two, then it Will go back to zero. Switch your leads around on the cap and the same thing should happen. If so, The cap is good. If it looks swollen or oily it needs to be replaced. Hope this helps.

  • So my ohm meter shows infinite resistance until I touch the leads ... then shows some number of ohms ... falling quickly to 0.01 or thereabouts. So ... that looks like a good capacitor? – Daniel Wilson Jun 24 '17 at 4:14
  • That capacitor is broke. 😞 – ArchonOSX Jun 24 '17 at 9:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.