In this video, we're talking about run capacitors specifically focusing on how to test them under load. Run capacitors play a huge role in Motors running efficiently, cool and reliably by storing and releasing current resulting in a controlled phase shifted current on the start winding of the motor. To test a capacitor under load, you need to Ure the system is running, but remember safety first. Always wear the proper personal protective equipment when doing so and only do so when you can do so safely.

This underload test is a handy way to test a capacitor with the unit running and is really useful as part of a regular maintenance procedure. I Still suggest a usual bench test in many cases and as a final check before actually replacing a capacitor. Once the underload Test shows failed or out of specification, an accurate multimeter is essential for this task. Its purpose is is to measure both the voltage and amperage reliably and must be done for the results to be accurate.

take an amperage reading on the wire that connects to start on the motor. For a compressor, this is the wire connected to Herm on a dual capacitor and for the fan, it's the wire connected to fan on the Dual capacitor. However, a common mistake is getting skewed readings due to interference from other circuits. To avoid this, always ensure the wire is centered in the amp clamp and isolated as much as you can.

So now the simple formula: measure the amperage on the start wire and multiply it by the fixed number 2652. Next, measure the voltage across the capacitor being tested and divide by that voltage number. So once again, amperage on the start winding multiplied by 2652 divided by the voltage across that capacitor. Repeat for both the compressor and the fan capacitors.

Keep in mind, once again, a good meter and proper clamp placement is essential. But what do these measurements mean If the capacitance or MFD or microfarads you measured is less than 10% of the expected value, generally, that's when going to replace at that point I'm also going to do a bench test to confirm. Keep in mind this is the standard I use. Some will look at the plus or minus value range on the capacitor as the guide, but keep in mind that this plus or minus value is just the out of thee boox acceptable range from the manufacturer.

If the microfarads is above the expected rating, don't rush to conclusions often. it might just be a measurement error. Capacitors do not fail with a higher rating than they came with out of the box. To make this easier and to guide the entire process, the HVAC School app has a free calculator you can use for underload capacitor testing that provides all of this information so you don't need to remember the equation.

Contrary to what some may say, having a fully functional capacitor is very important for the longevity and efficiency of the HVAC system. And capacitor testing on Maintenance and Service is a really good practice. Thanks for watching if you're willing, give this video a thumbs up and drop us a comment Don't forget to hit that Bell icon to stay updated with all of our future videos. And as a quick reminder: HVAC School isn't just a YouTube channel.

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