If it's a single phase, compressible you'll note that you have an ohm measurement, a measured value between run and start, but you will not have a measured value between run and common and start in common with an ohm meter. Again, this is with power off being really safe, making sure that all capacitors are discharged and at that point, you're going to test this at the terminals of the compressor all right. So this video is about diagnosing a compressor that won't run now in this video. I'm not going to talk about a compressor, that's tripping a break or blowing a fuse.

That's gon na be a different video, so watch for that one. But this video is specifically about a compressor that won't run so first off. Some of you who may be watching may not be professionals. This video is for professionals only there's some terms that aren't gon na make sense unless you've already worked on air conditioning and refrigeration or been to specific training for this topic, so warning disclaimer.

This is for professionals only we're talking about the compressor, obviously we're talking about the pressure increase or the heart of the system that actually moves refrigerant through the circuit. So when the compressors not working when it's not running, then you're not doing the work of moving refrigerant and therefore you're not doing much of anything other than maybe blowing some air around. So, first off, when your compressors not running, how can you tell generally, you can tell because you can't hear it, but sometimes it's hard to tell because there's a lot of noise and the area. Maybe there's a condenser fan nearby, and so you can always confirm whether a compressor is or isn't running or trying to run, which is the term that we use for a compressor that is trying to start drawing high amperage.

What we call locked, rotor, amps or in rush amps and then going off again on thermal limit or a compressor protector, whatever term you prefer there, so an amp clamp is a really good way clamped around the common wire or one of the leads on the compressor. Another thing to mention is: there's two different types of compressors: I'm going to refer to here, three-phase compressors, which are generally seen in commercial and industrial environments and then single-phase compressors, which are used primarily in residential and light commercial environments. They function in very much the same way. They all have, I shouldn't say all, but most of them are gon na, have three terminals on them, but the way that they're wound internally and the incoming power is going to be quite different.

So you want to know something about the difference between three-phase and single-phase. Before we go on, there is some difference in how you diagnose these compressors, based on whether their three phase or single phase alright, so step one. This chart comes from Emerson, so this is Emerson and slash Copeland, and they have this really. Nice flow chart that kind of walks you through how to diagnose a compressor.

That's not working so step number one. It's not running. You've confirmed that either through noise or amperage or hopefully both step. One they're listening here is make sure that the compressor has time to reset if the compressor has been trying to start - and maybe is locked, you want to give time for the thermal overload inside the compressor to turn back on now.

In the case of a three phase compressor, the thermal overload or compressor protector is designed to break all three legs of power at once, so it's kind of in the center of all three windings. If it is a single phase compressor, then it breaks the common terminal or directly behind the common terminal before it connects to run and start. So here are some quick diagrams to show you. This is single phase, and then this next one is three-phase just giving you an idea of how those are wound, and so most compressors are going to have some sort of overload or thermal limit, and you want to give that time to reset now, for compressor is Overheated, you can often tell that either by using a thermal, imaging camera or a laser thermometer, even just the back of your hand, quickly just to kind of test and make sure whether it's hot or cold, if a compressor is stone-cold at that point, there's not a Whole lot of sense in waiting any longer I mean it's, the thermal mass of the shell of the compressor and all the metal parts and the compressors that get really hot, and so if the whole thing is cold, when you come up to it and it's not Running at that point, you can be pretty assured that it's not out on thermal limit.

I mean give it maybe a minute or two, but at that point you can be assured that there's something else going on the next is to check voltage at the compressor terminals. Now I suggest checking on the line side of the contactor, which is the potential coming into the contactor and then the load side. First and then you can check at the terminals to make sure that you don't have any broken, leads or anything wrong with the wiring leading to the compressor again, whenever you're going to be taking the cap off of the plug off of a compressor, you want to Be really careful, sometimes it's not really practical to check at the terminal of a compressor if it does have a molded plug, because at that point you have to pull the molded plug off in order to check there. So you're gon na have to then remove it.

Then check inside the plug itself, not at the compressor terminals. If that's the configuration, if you have the proper voltage next, you want to again check the amp draw if you have higher excessive amps, meaning that it's going in and out of thermal limit or protection or drawing very high amps, then at that point, they're suggesting that You check winding resistance and resistances to ground. I would also say before you even get to this step, maybe even before you all that time for the compressor protector to reset, I would do a inspection on single-phase equipment of your capacitors of any of your start gear of all of your wires. Just do a really good, solid, visual inspection, your contact or any a starter, or anything like that.

That's in the circuit to make sure that there's no damage and then actually check your micro farad's on your start, capacitor and your run capacitor to make sure that they are functioning properly. But assuming all that's fine now is, if perfectly fine time to start checking your to ground resistance and your resistance from leg to leg. If you still have no amps, then that's sign that you want to make sure once again that your thermal overload is not tripped. At this point, though, this is where I would suggest going back and owning the compressor anyway, because you can tell whether a thermal overload is tripped on a compressor with an ohm meter with the three-phase meter.

What you'll find is that all legs are open to one another. That's generally an indication of an open thermal overload. If it's a single-phase compression you'll note that you have an ohm measurement, a measured value between run and start, but you will not have a measured value between run and common and start in common with an ohm meter again. This is with power off being really safe.

Making sure that all capacitors are discharged at that point, you're going to test this at the terminals of the compressor now they're suggesting that you check to see if you have proper resistance on each winding in a single-phase compressor, you have two windings. You have a run winding and a start winding, and the common terminal is the point in between them. If you're working on a Copeland compressor, you can actually go on Copeland, mobile comm and you can find what the design resistances are of each winding. Keep in mind that a lot of these measurements that you take are reliant on you having an accurate meter and you making really good contact with the terminals really like using alligator leads or a crocodile clamps whatever you want to call them for doing these measurements, because It just makes it I've been work firm, one run all right, so the Copeland mobile line up here, let's see if I can scan this model in and down you can see it's an AR 22 single-phase compressor.

We can look at physical properties came charged with mineral oil all that, but then you can even test performance on it. But if you look at the electrical section here, it will show you what run capacitor should have on it. It will show you the winding resistances. This is what I want to get to so if it is a Copeland compressor, you have access to this through the Copeland mobile app.

If it's other brands may be a little more tricky to find, but you can go to the manufacturer to get it in the field. Sometimes it may not be the easiest to get, but now we know that our start winding should have one point. Eight five ohms, plus or minus seven percent and our run should have 0.475, and if we do the math on this you're gon na see like we discussed that that amperage is really really high, but because it's an inductive load, meaning a magnetic load. That's what we would expect so, let's go ahead and see if these are the resistances that we're seeing from leg to leg and then we're also gon na check from leg to ground on this compressor.

So I'm connected to run in common with my alligator clips, which, coincidentally on rusty terminals, makes a big difference, because you get more contact points can be really tricky to do it with just the terminals and so between common and run. I have point five three will say 0.53 compared to point four seven, which is what we were supposed to have that's well within range, especially given that you know we're looking also at the accuracy plus or minus of the meter, so we're not gon na get too Persnickety about this, because it's a pass/fail to have a test anyway, we're not gon na replace a compressor, just cuz, it's a little out, but you can see it's it's measuring on the run winding close to what it said in the Copeland mobile app. So now, let's try start sure now point one nine five so again in range between start and common, so the actual windings themselves are in range. Now again, you would have to look at manufacturer specifications to know what what the own values the resistance values on these windings should be because they're just gon na vary so much, and so people who try to give you rules of thumb for this just isn't accurate Enough, so you can see here using a very basic field: peace meter that we're measuring under 20 mega ohms between currently I'm measuring from run until ground to ground.

If I go to calm - and it will probably even be less based on this - I'm not gon na condemn the compressor, but I am gon na say that we'd likely do either have some winding breakdown or potentially oil contamination going on that is leading to you know, Pretty low even based on a Copeland's literature, you get below 20. That's something to look for, and you can tell you can see here. This isn't a fancy mega meter. This is a very basic inexpensive field, peace meter and we're already showing that so, let's go ahead and test it with a mega ohm meter, though, and just see what it shows okay.

So this is copeland bulletin, a efore 1294, which talks about mega ohm values of copeland compressors. It covers that first off they don't really want them to be tested with a mega ohm meter. But what it essentially says is is that if it's a swing - and this is only for a copeland scrolls - if the mega ohms are under 0.5, so under 500,000 ohms, so under 500 K ohms, then you can condemn them. But if it's above that then they're good, the problem is, is that the most popular mega meter out there shows failed under 20 mega ohms and Copeland agrees that under 20 mega ohms, you probably have maybe some oil contamination or something going on inside the system.

But it isn't necessarily a compressor problem and based on my testing and experience, I agree with what they're saying here with open motors or even reciprocating compressors. You will see much higher mega ohm readings, but for Scrolls, specifically, unless it is below 1/2 of a mega ohm to ground, then you shouldn't condemn it. Okay, so I have the terminals set up in the same way as I did with the little field piece here. This is a very inexpensive insulation, tester Victor that I actually bought off the Amazon and I've tested it against my fluke, which I actually don't have with me right now, cuz it's out in the field, so I'm just gon na use this I'm gon na use the 500 volt scale, which is what you would use on a 240 volt, single-phase appliance like this.

If you're doing hundred twenty, you would use 250. Generally generally, it's accepted that you use double the operating voltage and power on. So I'm gon na do is just press to test and sure enough very close to what I was measuring with the field piece showing a little bit higher 5 mega ohms, but still definitely under the 20 under the 20. As shown on the cefco M 500, which is one of the kind of industry standards, so this meter would show that this compressor was bad.

Just something to know that on Scrolls, based on my experience and Copeland's literature, you're not gon na want to go off of what that's telling you there. If you find improper resistances that are well outside of what the factory suggests, then that's when you would go ahead and replace the compressor at this point now, I do need to mention a short to ground condition, because this is one that a lot of people get Confused, especially with scroll compressors, compressors and especially scroll compressors will often measure a resistance measurement to ground from the terminals and ground in this case is generally, you take one meter lead and you scratch it on the discharge line or suction line, and you measure from each Lead to ground now, when you do that, recognize that those windings are inside the refrigerant and the refrigerant oil, in that compressor, which is even worse than a scroll, because the scroll is motor side down, which means that motor is really immersed in that oil and refrigerant. It's also very close to the shell, so you will measure a measurement there now Copland suggests that anything under 0.5 mega ohms is failed, but between 0.5 and 20 mega ohms, a lot of people will say failed, but Copeland does not suggest that that is a failure. May just be a sign of maybe a little bit of oil contamination, something like that going on or maybe a little bit of winding breakdown, but not a complete failure.

So make sure that you know that, just because you measure some measurement in the mega ohm scale from a winding to ground, that doesn't mean that the compressors fail. Necessarily at this point, if you do measure improper resistances, meaning you're, measuring a resistance to ground of under 0.5 mega ohms or if you're, measuring well outside of the design range for the windings themselves, knowing that you're using a good meter and connected properly. At that point, you would have a failed compressor, but you need to note exactly what measurement you were taking. That was out of specification before you condemn that part.

Now, let's say that your overload does not reset so you've, let it sit for an extended period of time, maybe even run a garden hose over it over it or something. Now this could be four or five six hours even up to days for certain compressors if they have a lot of thermal mass, and you know that that over-over load is still not resetting at that point, you're stuck replacing the compressor. Now there is a key difference here if you were to measure on a single-phase compressor and you measured between, run and start, and you measured an open value that would be a sign of an open winding, which of course will never reset not an open overload. So what I compressor most of these things that you're going to be checking are gon na be visual and I check the start gear again.

This is a capacitor. This is a contactor that I would go ahead and suggest changing. Just because you see we have significant carbon buildup, not to say that it is a problem that it could become one. You know check your run capacitors.

You can check your your winding resistance against what Copeland's specs are, or whatever manufacturer you're using. You know check your terminals this, I need to take a wire brush to get those cleaned up a little bit more before I put the terminals back on. If you have one, that's not running, coppens instructions say wait for it to reset. What I would generally do is just kind of touch with the back of my hand like this and just feel if the casing is still warm, the thermal overload is actually going to be generally directly behind these terminals in here, and so you'll have kind of quick Resets, if you've got an issue with maybe the windings overheating, because it's trying to start, but it's cases where the system has run hot for a significant amount of time.

That's where it's gon na take a long time for that to reset some people will use a hose to cool it down those sorts of things. But it can take a long time for this shell to cool and that's one that you really don't want to get wrong. Like I mentioned in the case of a single-phase compressor, if you have an Oakland thermal overload, you will find open line or no continuity between common and run and common and start. But you will read an ohm value between run and start because run and start is the additive amount between common and run and common in start? So if you take common or uncommon and start add them together, you'll get running start.

But if your thermal overload is open, then you won't measure ohms from start to common and run to common, but you will read an ohm value between run and start. So that's how you can tell for sure whether or not the thermal overload is still open, and if it is, you want to make sure you give it plenty of time to let it reset often longer than you think you need to mistake, is doing your testing Up at the contactor, rather than at the compressor itself, become a master of the obvious. Look. Look at your leads.

Make sure you don't have any rub outs, make sure you don't have excessive corrosion on your terminals, make sure that everything is well connected. These are things that expert technicians do and often make quick repairs head of something that a junior technician would end up. Condemning the entire compressor always put the covers on to make sure that you're not gon na get any rain water or moisture and behind corrode the terminals. So when it says checking the voltage at the compressor terminals, you would check them here with voltage applied.

But I would actually start up at the contactor and make sure that I have the proper voltage incoming and then the proper voltage outgoing from the contactor. Again, this is single phase with three-phase. You would check all three to each other. Make sure that you have the proper applied voltage, that's rated on the compressor, we're gon na move over quickly, because we didn't touch on this.

What happens if you find that you have improper or no voltage well, obviously, at that point it's got nothing to do with the compressor. You have to find the source of the problem and you have to keep going upstream on the circuit until you find the source of the problem. Obviously, in this case, we have a compressor not running so you're, not really testing under load. You're, not gon na see significant voltage drops or anything those have to be done once you get the system up and working, but if you have a compressor, that's not running, and it's due to voltage that is too low or no voltage at all.

You have to figure out. Is it an open contact or some sort of open safety down the line? That's causing you to not have your voltage or is it something in the high voltage electrical circuit? Maybe a trip breaker herbal infuse so on and so forth. So once you figure out that cause, then you can go back and figure out. What's going on with the compressor all right.

So let's say that you've measured the resistances and the resistances look okay, so they're within range. Again I keep saying it but make sure you do this safely and whenever you measure resistances measure them at the compressor terminals. Next you're going to go back and you're gon na check, wiring again you're gon na make sure that everything is wired properly. You're gon na double check your start gear, all of that and then you're gon na move on.

So this is once you visually inspected. Your connections you've used a meter and you've hopscotch through the circuit to make sure you're not losing voltage anywhere and you're, establishing that you are receiving proper voltage at the compressor terminal, so you're going through. All of that, when it comes to things like start components like run, capacitors or start relays, and all that you can also with Copelan, to use the Copeland mobile app to look up exactly what size capacitors should be on there. You don't want to just trust.

What's in front of you, especially if something's been in service for years, it's very possible, somebody could have put something incorrect in the circuit, so make sure to check. All of that. This is all all this start. Gear is generally going to be only in single phase applications and three-phase applications.

There may be some part Start strategies depending on you know what type of motor you have, but generally it's going to be a little bit more simplified in three-phase next thing. You need to make sure is that the compressors, properly applied double check and make sure that this compressor is the right compressor for the application, which can also easily be done on Copeland mobile. If it's Copeland, if you're working on a compressor other than Copeland, then you're gon na have to go back to the original manufacturer data to ensure or just refer to the data tag once you've done. All of this just make sure that pressure is equalized in the system.

Sometimes pressures being unequal can cause some challenges and so make sure that the pressures are completely equalized in the system that the system has been off long enough and then restart again and see if possibly in runs. If it does not restart, then that's when you replace the compressor. This is very practical at this point. You've done everything you can do the compressor still not starting now.

It tends to tell me at that point. You've done something wrong because you've measured your resistances in your windings, so something should be happening and if it's not means you probably took the measurement improperly, but this is where this chart goes. It basically says if it's still not starting after you've checked all this, then replace the compressor. What I most often see is people saying replace the compressor earlier because they get fed up with trying to test everything properly and they get a little overwhelmed and that's not something you want to do if you're getting to this point, you need to make sure that You're double-checking everything you've already checked.

If it does restart, then just check to see if you have high amps or you have normal lamps. If you have high amps, then you need to take a look at whether or not there's something in the system that could be causing it or in some cases you may be replacing them protect or something like that or the compressor. If there's an internal failure to the compressor, what we want to make sure of is once you do, get the compressor operating that you're checking all of the system conditions to ensure that there's nothing in the system. That's causing high amperage, which can also lead to compressor damage now, there's a whole laundry list of things that can damage your compressor and we're gon na do a separate podcast just about that all the things that can take out a compressor.

This is just a walkthrough of things to check on the compressor, and the list on this particular side when think pressure is not running, is make sure everything leading up to the compressor is correct. Check at the terminals for ohm to ground and terminal to terminal to see, do you have an open winding? Do you have an open overload or possibly do you have a shorted winding, either winding the winding or to ground which, in both of those cases, that's not going to necessarily cause the compressor not to run it's more, so gon na cause a blown fuse or blown Breaker, but it's worth checking while you're already there just to see if you have any damage and again reminder just keep in mind that when you're, using a mega, ohm meter or a multimeter that can measure in the mega ohm scale just be very careful not to Just follow a bad light, a light that just says bad, because in some cases, especially with Scrolls, you can have a scroll that does measure under 20 mega ohms to ground and is not failed. Do they go? That is how to diagnose compressors. That is directly from Emerson and Copeland.

Thank you to Mike nipper for giving me authorization for using this and for providing me with this guide. You can take a look at his compressor, teardown class in our youtube video that we did with him as well thanks. So much for watching we'll catch you on the next one.