How to Test an HVAC Motor Capacitor | Spec. Sense

[Music] hi I'm Vance and welcome to spec cents capacitors are an essential component in many single-phase motors this includes furnace blowers air conditioner fans compressors and pumps capacitors store electrical energy as an electrical charge builds and releases between the dielectric plates the voltage will be delayed slightly as it lags behind the charging current this creates a magnetic phase shift in the start winding providing the torque needed to turn the rotor if the motor isn't starting or if it starts slowly and it's likely that the capacitor has failed sometimes the capacitor will bulge or leak when it fails in other cases the failure is internal and can't be seen in this episode we'll look at how to safely discharge a capacitor and how to test capacitance with a multimeter on the capacitor you'll see two ratings capacitance and voltage the voltage rating refers to the maximum voltage that the capacitor can be exposed to you can use a capacitor with an equal or higher voltage rating but never with a lower rating as this can result in capacitor failure the capacitance expressed in micro farad's is a rating of how much energy can be stored in the capacitor this should be matched exactly start capacitors have a high capacitance anywhere from forty to three hundred microfarads they are used only briefly during the startup sequence in capacitor start motors run capacitors have a lower capacitance around five to eighty micro farad's they are permanently wired into the circuit and are used in permanent split capacitor motors Dule run capacitors are used to support two electric motors like in air conditioners that use both the compressor and blower fan they will have three terminals marked common fan and herm or hermetically sealed compressor they will have 2 micro farad ratings the higher rating is usually for the compressor and the lower rating is for the fan always be safe first disconnect the power and gas before accessing your capacitor be aware that even when the power is off they can still hold a charge always assume capacitors are charged as there is a risk of a serious electrical shock before testing discharge any stored electrical energy in the capacitor you can place a resistor or screwdriver with an insulated handle across each terminal this will short out and discharge the capacitor on a dual capacitor first touch a screwdriver from fan to common and then firm to common to discharge both capacitors to test the capacitor use a multimeter with the capacitance testing function now touch the probes to each terminal if the capacitor is good then the multimeter will show a reading very close to the rated value capacitors can lose capacitance over time and outside a five percent tolerance any change in capacitance will negatively affect the motor performance if the multimeter shows a significantly different reading then it's best to replace the capacitor for dual run capacitors first test from firm to common then test from fan too common these readings should also match closely to the two rated values you can also test if the capacitor has shorted to ground set the multimeter to ohms and touch the probes from each terminal to the side of the housing the multimeter should display Oh L or open-loop as no terminal should have continuity any resistance then the capacitor has shorted to ground should be replaced now you know how to safely test a motor capacitor if you liked this and want to see more tutorials and informational videos then subscribe to our Channel and if you need help you can call or visit a name relocation to talk with our knowledgeable staff thanks for watching you

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