Air Conditioning Capacitors and Why They Fail
If you own a home with an HVAC (Heating, Ventilating and Air Conditioning) system you have very likely had a capacitor issue at some point. In the video, Kalos Co-Owner Bryan Orr talks about what a capacitor is, what they look like, what they do, how to read them and why they fail (hint: we aren’t really sure)
Capacitor Video Transcript
Hi I’m Bryan Orr. I’m one of the co-founders and co-owners of Kalos Services. We’re an HVAC electrical and construction company in central Florida. Actually out of Clermont which is in west side of town. We’re not that far from Disney World. One of the most common questions that I get … In fact, one of the most common questions that I find myself asking is why do capacitors on air conditioners fail so often? That’s the question. Why do they fail so often?
First off, this is a capacitor. This is the top, you got three terminals. This is what’s known as a dual run capacitor. Not to be confused with smaller capacitors that are on electronics boards and then also even in an air conditioner you’ll have what’s called a start capacitor which is generally black and it’s a plastic coded capacitor of a much higher rating.
The difference between a run and a start capacitor is a run capacitor is actually in the circuit at all times. Every time the motor is running. A motor that requires a run capacitor in an AC. Those motors are known as permanent split capacitor motors. Tech talk, all that really means is this is always in the circuit. If this capacitor fails, what will often happen is the motor either won’t start, it will run backwards, it will run hot, it will run inefficient. It just depends on the type of motor and how much load it’s under.
A dual capacitor, what’s up with a dual capacitor. It has 2 features. That’s why it’s a dual capacitor. It has your common terminal here, which is the common point between the 2 halves of the capacitor. You have the fan terminal here which is where the outdoor fan connects. Then you have the HERM which is kind of a funny name, it’s kind of an old school name. It means herm for hermetic compressor. That just means a sealed compressor. That’s the big pump in your air conditioner on the outside.
When these fail, basically the system stops working. Not only that, it can cause damage to the motors that it’s connected to when it fails because those motors run very hot and keep going out on thermal overload every time it fails. Again, this is a dual run capacitor. This type of capacitor is in your air conditioner on the outside. These are the kind that most often fail. They’re 2 in 1, two capacitors in one. You also will have capacitors often on your inside unit on your blower motor as well. Those fail less often but they do sometimes fail and they’re a little bit smaller.
Let’s talk about how these are rated. I know this is a little technical but it you’re looking for a capacitor, you’re wondering what’s up with your capacitor. I want to teach you how to read the nomenclature on this. If you look here, you’ll see it says 40×7.5 MFD. This is something that will vary from manufacturer to manufacturer. Some of them will say MFD some will say MF and some will just have a omega symbol. Which is a Greek symbol that looks like an upside down U. What this means is 40 MifroFarad and 7.5 MicroFarad. The smaller of the 2 numbers is the MicroFarad rating of the fan capacitor and the larger of the 2 numbers is the MicroFarad rating of the big capacitor for the compressor. This means that your motor on the outside is running on a 7.5 MicroFarad capacitor and the compressor is running on a 40 MicroFarad capacitor. MicroFarads, that is how you rate a capacitor. There’s no other way to rate the actual capacity of a capacitor other than MicroFarads.
This next part is where a lot of people will get confused because it lists a voltage rating here. 370 or 440 VAC or volts AC. A lot of people will say but my air conditioner’s only 240 volts or 120 volts or some people call it 110 or whatever. That’s not what this means. This doesn’t mean that this is the voltage that this runs on. This is the voltage at which the capacitor breaks down. Now funny things just started happening because for years manufacturers were installing 370 volt rated capacitors and the replacement market was using 440 volt capacitors. This means the maximum voltage that the dielectric fluid will actually be bridged. Or I should say the minimum voltage at which the dielectric fluid inside will be bridged.
Here’s the point. That number means the maximum voltage that it can handle. A 440 VAC capacitor or a 440 V capacitor is better than a 370. The problem is people kept getting confused because if they had a 370 they would want to replace it with a 370. This manufacturer says 370 or 440 and they do that just to eliminate confusion from consumers primarily who think, oh my gosh my service company put in the wrong capacitor because the voltage says something different. They started putting both on their just to ease people’s minds. Truthfully, if it’s a 370 or 440 it’s actually a 440 and that’s good. Over here it says hertz. That’s the cycle rate. That means it says 50 or 60 and that means that it can work in US or Europe.
What you really need to know, what it comes down to is … What you really need to know is the MicroFarads on your capacitor. Given this is a dual, that means that the MicroFarad rating between C and herm is 40 and the MicroFarad rating between C and fan is 7.5 because again this is 2 capacitors in one.
Now to get to the real question that you’re asking. Why do they fail? I don’t have an answer to that question. When I first started in the trade 16 years ago as a technician. It was very rare that you would see capacitors fail. When I say very rare it was as common as a contactor failing or a relay or any other of the devices in an air conditioner. Now a days, capacitors fail at an extremely high rate compared to other components. The only thing I can say is that they must be being manufactured differently. The manufacturers who make these capacitors. I’m not talking about the equipment manufacturers because the equipment manufacturers, they don’t make their own capacitors. They’re buying them from other people. The manufacturers of the capacitors themselves, they’re just not making them like they used to. I know that sounds really weird. In fact I usually criticize people for that. This is based on real fact that I’ve seen. Is that these are just failing more than they used to.
Now, here’s the good news. We use largely this brand which is an American manufacture brand. We use a couple brands but this is the most common that we use. We’re always looking at replacing the 440 volt capacitors which hold out better. We’re usually whenever possible, using this American made brand here. We’re seeing much lower fail rates on these capacitors than we’re seeing on other brands. Still not perfect but much better than what we see otherwise. Even a few manufacturers are starting to go to using this brand in their systems. When they do we see them drop. By in large, most manufactures are still using capacitors that have high fail rates. This isn’t one brand over another. It’s not like Trane is better than Carrier or Lennox is better than Trane. They’re all using capacitors that seem to have fairly high fail rates.
One thing that an old timer used to tell me. I don’t know if this is … I can’t prove whether or not this is true. He told me that these are designed to be installed upright and so that when people install them on their side or upside down that that increases the fail rate. I have no way of knowing whether or not that’s true. I’ve never scientifically tested that. Ever since he told me that I always try to make sure that these are mounted upright whenever possible.
Another thing that will come up is people will look at different ones, different capacitors and they’ll be different physical sizes. That doesn’t mean anything as far as I can tell. It’s just the physical size of the casing that they put the plates in. What’s going on inside here. There’s actually oil that’s … I think it used to be castor oil, I’m not sure if it still is, I think it might be. Let’s see here if it says. It doesn’t say on this one. There’s oil inside here and there’s some plates that basically wrap around in here and what happens is this just stores a charge. That’s what it’s designed to do. It helps get a motor started and running and efficiently and in the right direction. Not to get to hyper technical on how it works.
What happens when they fail is that for some reason the charge bridges those plates or bridges the dielectric fluid and it causes it to fail. Generally speaking when these fail what you’ll find is the top here, instead of it being flat like it is here. It’ll actually bubble up and that’s by design. The top is actually the thinnest metal on the entire thing so the rest of this metal is very thick heavy gauge metal. On the top it’s a little bit thinner so if it over heats or if that dielectric fluid is bridged, this top gives and bubbles up. It’s basically so the thing doesn’t explode. It gives in one direction. If you ever see a capacitor like this where instead of the top being flat it’s bubbled. That’s an indication that it’s failed.
That’s pretty much it. In order to test them either you can see that it’s bubbled or in the case that you suspect that it’s weak. You should really use a meter that has a MicroFarad gauge on it. There are ways to test them while the system is running. In most cases you’re testing them because the system is not running, the compressor or motor are not running so that’s why you would use a meter, a multi-meter that has a MicroFarad gauge on it.
Ultimately, the question being asked is why do they fail? I don’t have an answer. We’re in Florida. That’s the market that I know. Florida hasn’t gotten any hotter than it used to be. A lot of people say it’s heat but that hasn’t really changed. Some people will attribute it to electrical power inconsistencies. I haven’t found that the electrical power is anymore inconsistent now than it was when I first started in the trade 16 years ago. But we certainly do see a lot more failures. Hopefully it’s something that the industry of capacitor manufacturers will get on top of. In the meantime this little component here can cause a little bit of trouble with your AC. We’re the guys you can call to help take care of it with the least hassle and making sure that the systems working good and everything else. When we do run into one of these we replace it but not only do we replace it we make sure to check all the connections that there’s nothing that could cause it to fail. Test the entire system, check [inaudible 00:09:57] charge, go through everything to make sure everything’s working properly so you don’t have any further issues, heaven forbid.
Thank you for watching this again it’s Kalos Services. If you want to ever call us, you can call us at 352-243-7088 or visit us online at Kalos, K-A-L-O-S Florida.com, that’s kalosflorida.com. I’m Bryan Orr thanks for watching.