WHY CAPACITORS FAIL in Air Conditioners! Watch it Break!

in this hvacr training video we're going over why capacitors fail in air conditioning units so we're going to verify that this one is good and then you're going to see it fail in real time while the system is running [Music] next we're going to test this capacitor to see if it's still good we're going to test it while it's under load so i already have my multimeter set up so this one's going to read the voltage and current for our compressor coming off of the capacitor and this one is measuring the voltage and the uh current for the fan motor and so you can see one probe is here and one is here so we're measuring the voltage on the fan and the common which is connected right here on the capacitor and we're going to measure the current coming off of the capacitor right here so this is on the fan terminal over here you see we're measuring the voltage on the herm and the common and then we're measuring the current for the compressor so i'm going to turn the system on let it run for five minutes i'm going to show you how to test this while it's under load before we see this capacitor fail in real time the system's been running for about five minutes and you see a current of 6.32 on the herm which is the start winding of the compressor and we measure 357.7 volts so what we do is we take 6.32 and then we multiply that by two six five zero and you divide that by the voltage which is the back emf from the compressor and we're at 358. so we have 46.78 microfarads on that capacitor so that capacitor is good it's actually rated for 45 now let's check the fan and you see that we're measuring 0.7 amps at 363.5 volts so we're going to take 0.71 times 2650 divided by the back emf the back voltage from the fan motor which is 364.7 5.15 microfarads on that capacitor for the fan and so that capacitor is good and so now what i want to do is just go ahead and watch the top of that capacitor and we're going to see that capacitor actually fail so that capacitor has failed on the compressor side and also on the fan side you can hear both the fan and compressor are still running now if i turn this off uh the fan and compressor are not going to be able to turn on this time so the only reason that they're running was just because capacitor was installed in the very beginning current is very high on both the fan motor and the compressor right now in order to keep them spinning now we're going to allow power to the system and you're going to see a high current draw but you're not going to see the compressor or the fan motor turn on so i don't know if you can see this on the capacitor but this one is still good it's flat down in there but this one has a mushroom on it right there and you can see that the terminals on the top are kind of spread apart right here so this capacitor failed actually due to overheating on the bottom of that capacitor you can see it's bulged downwards here's a good capacitor it is completely flat and so you can see that this capacitor actually failed and if we were to go over to mfd so that's microfarads you can see that we are still reading zero so this capacitor is bad now we're measuring the microfarads for the fan motors we have one on common and one on fan you can see that we're reading 0.0 microfarads so when a capacitor fails they tend to bulge like this right here or like this and so that's just due to the heating of the dielectric fluid inside the capacitor and they don't always feel like that there may be some that feel with the fluid that basically comes out of the capacitor and other times it'll just look completely fine it may look a little rusty may look a little old and it may be bad but it may be good that's why you need to test them we test them either under load or isolated by themselves and discharged and so what you need to remember is this right here the capacitor so on a dual capacitor there is two of them and a dual means they have a shared common and so this is the oval style uh capacitor and then inside there's dielectric fluid and so that's a heat absorption fluid and so these are going to heat up while it's running and on these you're going to see on the inside it's just a little foil and then there is a another piece between each layer of the foil in order to separate the electrical sheets and so these are called sheets or panels and you can see there's a huge amount of wraps right here for this capacitor and so it's a little different than a start capacitor because the start capacitor will have thicker metal sheets and so this is from a a start capacitor that looked like this now i want to get into why a run capacitor would fail and so there's one big misconception about how run capacitors fail and that's when tech say that they failed due to high current well that's not the case and you saw that during while i was breaking the capacitor due to high heat at the base of this capacitor you saw our current was falling and so as we were losing the capacity within a capacitor on this little foil plate right here so this is a basically the inside of a capacitor and so you know i have a dual run capacitor right here and it's just sitting in the dielectric fluid as i was heating this i was making the plates fail and so we had less and less surface area on the foil in order to store the electrons and so really what was happening is the capacitor stored and released less current as i was heating up this capacitor and so you saw as the current was falling that capacitor was starting to fail so it failed on the compressor part of the capacitor first then after that on the fan side of the capacitor let's get into the reasons why a capacitor fails number one is the capacitors fail due to high heat and so if this shroud of the outdoor unit is in the sun all the time this capacitor is going to be really hot and so what could happen is the dielectric fluid could expand it could press outward on the shell of the capacitor like this or it could also push down at the bottom at the base right here and basically this is a telltale sign that a capacitor has failed here's another one where you see a mushroom top and so sometimes a capacitor fails and you won't see any any reason why sometimes when they overheat and the dielectric fluid is trying to get out basically it might come out of the side and leak out of the side of the capacitor so that's reason one they could overheat problem number two is that the lifespan of a capacitor is limited and it's really relative to the operating temperature and so the higher the temperature the lower the lifespan the less amount of hours that this is going to be able to to run and so what's going to happen is some of the foil is going to break down over time and that's why when you take a reading on a capacitor and you notice a lower microfarad reading than what the capacitor is rated for that means you've lost some of the plating inside so it's just not going to last forever number three is that you have a voltage rating on the side of the capacitor so if you have exceeded that voltage rating that could end up doing damage onto the plates inside of the capacitor so this uh the voltage on say the c and the herm while this is running is actually the back emf off of the compressor and so it's higher than say just a 240 volts in so we measured around 365 volts while this system was running and that's because there's back emf off of the compressor and so you could also have a lightning strike or some other reason where you have some type of a voltage spike that could do damage to your capacitor another reason could be that you have corroded connections right here so you could have just a bad rusty connection point and so this may or may not make the capacitor fail because what's going to happen is these terminals right here are going to heat up i've seen the weld basically attaching this to the capacitor just melt right off and so that's another way that this could fail is due to a bad connection point located at the top of the capacitor itself so that's it you could have overheated the capacitor you could have reached the life cycle end of the capacitor you could have had a high voltage some type of a voltage spike that has ruined the inside of the capacitor or you could have a loose connection at the top of the capacitor itself and so these do not fail due to high current because they control the current going to the start winding of the compressor and also the outdoor fan motor if you want to learn more about capacitors i have some other videos linked down in the description section below if you want to learn about hvac electrical troubleshooting make sure to check out some of the articles we have over at ac servicestick.com articles and while you're there make sure to check out our book the refrigerant charging and service procedures for air conditioning and so we go over how to check the refrigerant charge of a system how to prepare a system for refrigerant and also how to troubleshoot a running system so that's available over our website at acservicetech.com and also on amazon hope you enjoyed yourself we'll see you next time at ac service tech channel

Channel: AC Service Tech LLC

Views: 1,119,538

Keywords: acservicetech, repair, maintenance, how to, fix, hvac, hvacr, how do you, test, ac, service, tech, check, measure, read, superheat, subcooling, refrigerant, procedure, voltage, charging, temp, multimeter, freon, hvac class, hvac school, hvac training, capacitor, run capacitor, compressor, fan motor, probe, current, volatge, under load, microfara, emf, amps, MFD, bulge, dual capacitor, dielectric fluid, foil, panels, lifespan, operating temperature, corrosion, connection point

Id: 1_VtPzWxpsA

Length: 9min 44sec (584 seconds)

Published: Fri Jun 17 2022