Hey i'm brian with hvac school, and this is eric and we're going to be looking at a system that has an overheated compressor, so a compressor, that's out on thermal overload or thermal limit. What term do you normally use for this thermal overload yeah? So it's out on thermal overload the first thing that you're going to notice is the sound of it. You can hear the fan running, but you don't hear that deeper tone of the compressor running so for an experienced technician. That's going to be the first thing that you're going to notice what are some of the first things that you check when you walk up to a system that sounds like this.

Well, if the compressor's not running normally. The first thing i go to is thermal overload. If the fan's running - because you know the unit has power right, you know your contactor is probably working right if your fan is working right right. So the first thing i'm going to do when i walk into something like this is shut off power, and i will put a gauge on it to make sure there is refrigerant in this system.

You don't want to go through all the trouble of cooling it down. If it's flat, another thing is before you even put a gauge on: i'm always going to just take a look at the port and make sure that we're not showing signs of oil at the port itself. Exactly so always looking for visible signs of oil, because you wouldn't want to cover up a leak on the port, i'm going to be looking visibly at the capacitor pretty quickly too, because that can cause that a lot on single phase units and then i'm going to Be doing just a quick, visual inspection of all my wiring to see if maybe there's a terminal or something that's burned off, so there's some quick visual things that you're going to do, but once you do those things and you've confirmed that there is refrigerant in the System on the gauge, then we have to go into some basic electrical diagnosis, so our thermal overload is a switch. It's a switch that is a normally closed, open on rise, thermal switch and one of the most common reasons why a compressor won't run.

But there's always a reason why that happens in this particular case, we caused this unit to go out on thermal overload intentionally and just talk about what you did in order to make that happen. Well, it's kind of interesting because i've never been tasked with trying to make it go into thermal overload. So i just thought to myself i'll i'll make the compression ratio as high as possible. So i throttled the liquid down until i was getting a very low suction pressure and just let it run like that, so it had that really high pressure differential and wasn't getting any cooling from the refrigerant yep all right.

So now it's about an hour right. So now we're going to show what we've got, what we set up and then we're going to go through some diagnostic steps that you would take in real life. So i'm going to be doing the filming and eric's going to be putting his hands on tools, because a little better at that than i am first thing. We're going to want to do is find our disconnect and disconnect power to our unit and then we're going to use our meter on volts.

So we're going to we're going to go to volts and we're going to test voltage to ground. We got nothing now, something i probably should have done. First was test it while it was still live and then shut the power off. So i kind of skipped a step there, but it's always good to make sure your meter is working before you start touching stuff.

But a quick way to confirm that that compressor is off on thermal overload. Is we're going to switch to ohms now so we're going to switch from volts to ohms we're checking on the top of the contactor, our ohms and we're seeing 86 ohms and the reason we're seeing? That is because the compressor is actually not in the circuit right now we're only seeing the resistance through the fan motor and whatever else might be hooked to the contactor. If the compressor's in the circuit it'll be more like one ohm or very, very low, very low, and that's because compressors um, because they're higher current drawing, they actually have lower resistance. Lower resistance equals higher current so from here.

We would definitely want to look inside the unit, because another thing you could have is you can definitely have a wire burned off or something to not have the compressor run and to see that reading you could have a wire melt or burn off completely. So you want to do a quick, visual inspection in there at the compressor. Before we go any further now you do want to confirm. I like to confirm that, at the compressor that there's not like a break in the wire we're not seeing so you know, this can get a little involved to pull the fan, but we're going to pull the fan off, pull the plug off the compressor and verify At the compressor that it's open there all right, so the next step is we're going to remove after we get the fan out of the way we're going to remove the plug from the compressor or the cover and the terminals.

If it's that type. One thing to note here is: we want to take caution when we're doing this, because if the compressor is really hot and the fuselage plug's really hot, you can end up pulling the terminal out with the wire and dumping the refrigerant charge. It's always a possibility whenever you're, manipulating compressor plugs. It's just unfortunate reality, so just be prepared that, if that happens, that you know you have your proper equipment on probably should have a glove there's our plug and we're just going to home everything out all right.

So we're hooking the meter up to the pins on the compressor. This here is from uh start to run because we're actually getting something. But if we go from common, we have nothing common to run and common to start, both you're going to have a switch on this plug right now and i can't see in there, but it's not really important common to run and start are going to be nothing. The important part is hooking it up back correctly if it doesn't have this plug.

If you physically touch the compressor right now, you're going to feel that it is hot to touch and that's going to be an indication that it has been running. That's another way to tell that you have a thermal overload, that's still open, some people will wonder. Well how do i know that i don't just have an open winding. Well, we proved that because we had a closed path in between start and run, but then we had an open path between common and run and common and start, and we have a physically hot compressor.

So at this point, in order to get this thing running again, we're going to have to allow it to cool down exactly and that's a great point. If the compressor is cool, i would be more concerned that maybe the thermal switch opened and is not closing again. You could give it more time, but it could be that you know you have some sort of open situation there, but right now, while you have everything apart is a good time to actually own out your leads in between just to be sure that there's no other Issues that caused your problem, so we can take off all the leads to the compressor from this end and own them out one by one, all right. So now we have our alligator clip on this and you don't need one, but it makes life easier and this is conveniently labeled.

I believe that's going to be common, so we're good there. So what we're testing is we're testing from one end of this lead or wire to your compressor, to the other end with an ohm meter to confirm that the leads themselves are good and that the plug has connection all the way through so we've tested so far. That we've confirmed that it's highly suspicious. Our compressor is in thermal overload because it's hot to the touch and we have that open path from common to either run or start while we're in there.

We also confirm that our plug is good. All our wiring connections look good. We've done a visual inspection of everything. One thing we need to check next is our capacitor, because this problem could potentially be caused by a weak, capacitor or low refrigerant charge or two of the more common things deposit.

This dirty condenser coil would be up there too right, yep, anything that causes high compression compression ratio, anything that causes low return, gas density, otherwise known as low suction pressure or any electrical problems. So there's a lot of things that can cause these issues. The fact that the compressor is hot to touch makes it highly unlikely that it is a failed capacitor. A failed capacitor is usually that heat's going to be kept in the windings and so you're not usually going to have a really hot to touch compressor.

Usually, when it's hot to touch, that's an indication that it was running when it went out on thermal overload, so i've seen bad condenser fan motors cause it too. If the unit kept running and the condenser wasn't running right, anything that causes high compression ratio, high head pressure, low suction pressure or a combination of both low refrigerant charge, refrigerant restriction. Anything like that. In this case, we know that the problem is that we have a refrigerant restriction, because we intentionally uh caused high compression ratio by throttling the refrigerant through the valves.

Now, i'm just doing a quick check on the capacitor. We got 4.98 on the fan side and we have 35. So there's a 35.5. You can't say that's a good capacitor yep we're within our then our rated specifications.

So at this point we've done visual inspections. We've checked our capacitor. We've checked our leads to make sure that there's continuity through those there's, not a problem there and again that test isn't necessarily something you're going to do every time we just wanted to demonstrate the use of the meter, but at this point the compressor is overheated. So in the field, what would we typically do in a case like this, where we have an overheated compressor? Well, if the condenser is near a hose outlet - and it's not going to be objectionable to hose it down with a bunch of water like it's not going to create like a dangerous pathway or some something else like that, then just running a hose.

On top of the compressor, trickling water, you don't have to blast it. The best way is just to put it on the head and let it be like a nice stream that that continuously bathes the body of the compressor with water. Now some people will object to that, but as a field practice that is very common. It is better if you can stand just to shut it off and leave it off for a period of time, especially if you're on a facility that you can return to.

But in practice for a service technician, putting water on top is not a bad idea of a cool presser. I don't know if you've seen those by supko it's a magnet that you can hook a hose to and just trickle water over it so that it keeps the water kind of contained. So it's not spraying all over. That is a nice option.

Some people will say well: is it good to put the water on the compressor? Well, these things are outside all the time. So if the compressor is designed to have water hitting it, that's not a problem, but again you don't want to be making a mess, and some people will point out well that rapid contraction, because that could that cause problems i mean there is some potential there. I guess but we're working in a real world where we have to get these things cooled down, but in this case we're just going to let it sit for a while and we're going to come back to it in a little bit and see if it's cooled Down now, if you wanted to be able to know when that compressor reset, what would be one of the most practical ways of doing that, if you have your wiring reconnected, which is usually what i would do at this point, if i was going to start cooling, It down, i would start that and start reconnecting wiring as much as i could and you had the clamps. The clamps are a nice easy way to just clip them on there and set your meter to continuity, because the fan motor typically isn't going to trigger the continuity correct.

But once that compressor kicks back in you'll, hear your meter start beeping and you if you're cooling it down um you want to you want to go past that point. You don't want to just try to turn it right back on as soon as that overload relay makes again, because you can send it right back into thermal overload so right if you're cooling it with water, you definitely want to go a little longer and if you're Waiting for it to cool, i don't know why you'd be just sitting there with a meter on continuity, not doing anything, but you definitely would want to wait a while, even after that happens, right go ahead and hook it up that way, just to show what that Looks like if you're wanting to hook it up, which is a good point. If you aren't comfortable with wiring, it's a good idea to take a picture of it before so that way, you can reference it after before you turn the power back on when you're putting terminals back in place always make sure they're very snug on the spade. So right now we haven't put the fan back on yet, and we are testing from run to common at the contactor.

So there's literally you have to you, have clamps on ohm. You have meter leads with alligator clips on top of the contactor and we're reading ol right now, open line, no continuity or, i should say, infinite, uh, infinite, ohms, but that's just because the condenser fan isn't in place. If we were to put the condenser fan in place, you would measure an ohm reading, but it would just be a high ohm reading. So again, it's all a question of whether or not you want to put the top back on or not either way right now, this thing is going to start to ring and it's going to measure low ohms as soon as that thermal overload closes.

But if we were to put the condenser fan back in the circuit, we're going to see we're back at our 83 ohms now, that's the resistance of the condenser fan. Yes, as soon as that, compressor comes back in that resistance is going to go much lower and the thing is going to start to ring out all right. So now it's just a waiting game. I said, let's take a look at our wiring diagram, real quick and this thermal overload kind of what that looks like so it's very, very small on this diagram, but you can see, we've got compressor and we've got this thermal overload that illustration right there with that Kind of crooked line, that is, a temperature activated switch or temperature activated contact or safety, and so that is a single pole.

Single throw open on rise, normally closed. It's a mouthful thermal overload switch. You can see. We do not have a common winding, there's just a switch there.

So that's why, if our thermal overload is open, we will have continuity or a low ohm path between start and run, but we will have an open leg, otherwise known as infinite ohms between run and common and start in common. So right now we have our alligator clips between point 21 and 23 and it's showing an open path with no fan because it has to go through our thermal overload for there to be a path. If the fan is in, then it's able to make a path through the fan, but that's a higher ohm path, and so that's why it's not ringing out even with the fan connected all right. So now, as you can see, just like eric said we're down right around one ohm now, and so it's ringing out because of the continuity.

If you go back and remember, we were at 80 ohms before 80 plus ohms, when it was just the condenser fan motor. Now that we have both the condenser fan motor and the compressor in the circuit, because the thermal overload has closed because the compressor has cooled now we're ready to run. Obviously, we never want to turn on the disconnect or energize the system with the ohm meter on it. So we want to disconnect our own meter and now we're ready to run it all right.

So now we know that our thermal overload has closed, but let's talk again really quickly about the different things that we want to check to figure out why it opened in the first place, basically anything that can cause high compression or heat so suction line temperature back To the unit refrigerant charge, condenser coil, cleanliness, yup, the fan motor, proper operation, yep. One thing that's happened. A couple times to me is uh. You know you shut the unit off to do your check um and you let the unit run for 15-20 minutes, but you're.

Not monitoring condenser fan amperage and it's just keeps going up and up because the bearings had failed, so it runs while you're there and then after you leave it overheats and stops running and then maybe when you come back it's running again. So it's another good use for a thermal imaging camera as well, because you can actually track and watch is that condenser fan motor getting increasingly hotter and hotter as it runs, which is another thing. So your condenser fan motor also has a thermal overload in it. If the thermal overload on the condenser fan motor shuts that motor off then obviously you're not moving air over your condenser coil, your compression ratio is going to go sky high and then your compressor is going to overheat.

There's a lot of intermittent things. You got to look for, but we mentioned a few suction gas temperature returning. So if you have high superheat coming back that can cause it low, suction pressure. If you have a system, that's undercharged or if you have some sort of restriction, you know the good old, bad txv that can cause your compressor to overheat.

Like you mentioned airflow over the condenser, if somebody put the wrong fan blade on it, i mean i've seen that somebody replaces a fan. Blade puts the wrong one: you're, not getting the right amount of air over it or the blade is causing too much load on the motor which is causing it to overheat over time that can cause it. So there's a lot of different things. You want to check, as well as all of your electrical things, so once we get this thing running, we want to check our amperage on both our compressor and our condenser fan.

We also want to check our voltage make sure that that's in range with it operating whenever you're checking voltage. It's really only valuable in these sorts of circumstances when it's under load, when it's running, let's make sure that that's where it's supposed to be, and then we like, we already did check the capacitor. That's an obvious one, as well as visual inspection of all of our different terminals. One thing to note, as you were, on checking the condenser fan, having a meter with good amperage resolution like uh two places to the right of the decimal.

I like to keep that on the fan and watch that closely, especially if i'm not seeing anything else. That's given me a giveaway as to why it happened and if you start seeing the amps they're just creeping up creeping up creeping up, you probably have uh failed, condenser fan motor and after about 30 minutes, or so it's just gon na stop running yeah. The trend increasing and current - and that's a really really good way to look at that all right. So we're not going to do any of our refrigerant tests because we know what's wrong with this, but we want to show some of the electrical measurements that we take once we get the system running.

So the first thing we're going to look at is amps at the compressor and condenser fan, make sure they're in range with your nameplate rating or if it's an aftermarket motor go by the rating of the motor or compressor. This is the factory motor and we're drawing 0.6 and a lot of these on the newer units. They can be right at the edge of where they say, they're going to be, for whatever reason, so this actually says 0.6 full load amps, and it's pretty much running. I mean it depends where your meter is too.

You know we're getting like 0.54 and if your meter doesn't have two lines of resolution, it's probably going to round up. But this would be one to keep an eye on is to make sure your meter's in a good spot. And if that keeps trending up, then definitely something to watch out for so we're also going to check our voltage. We can check it in and out of the contactor we might as well since we're at this point.

It's really easy to do now, with the cover off. You see, we are at 209.7 volts and we can check our voltage drop across our contacts, so this shouldn't be a significant amount, because we essentially have both meter leads on the same point. If that switch is doing its job and then we can check over here, so everything looks good there and it's it's important to mention on this. This is a 208 power supply.

So that's why we're measuring voltage that's lower than what we normally see, but it's still within range, looking at 208 on this, because it's a commercial panel, that's feeding this unit, which is more common to see 208, but the unit's rated for it. So that's fine in this application. You probably won't see that much in residential, maybe apartment buildings, depending how big they are to measure our low voltage power. So i'm going to measure our low voltage just for the heck of it not really related to our problem, but we're here to measure it and we're at 23 volts.

So in this case we may actually have a transformer. That's not properly tapped. It's probably not tapped for the application, but there again this is a trainer unit. So what is it going to be plugged into right? You don't really actually know until we do it, so we would have to change that.

We should change this tab. If it's a permanent, install right, well, hey, we can show how to do it, at least. So, that's good! If we're looking at our refrigerant charge. Now our suction line temperature is a big one to look at as well.

As you know, discharge pressure and liquid line temperature, but this is how well your compressor is going to be cooled off by the gas coming back and copeland recommends no higher than 65 degrees when the system's running at its uh, when it's running at its design conditions. So right now we're a little high, we're running a 91 degree return, so we are seeing elevated suction pressure and, along with that, elevated suction line temperature, just because we're not inside the design of the system, but typically this would be. You know starting to get in that caution area if your suction line temperature is that high, when the house or the space is down to temperature yeah, we need to make sure that we let it run long enough, but based on what we're seeing right now or Sub cooling, you know if this system had run 20 minutes or so that sub cooling does look a little bit low, so our super superheat is on the low side, which that would tell us that it shouldn't be overheating. Of course, we know that we solved the problem by taking the restriction out of the system, but we're really looking at go ahead and swipe over and show compression ratio.

Compression ratio is a really big one that we look at, and currently our compression ratio is actually on the low side, so that isn't really giving us an indication of anything that would cause us to go out on thermal limit head pressure is not abnormally high. Our suction pressure is high, but that's just because it's 91 degree return air temperature in this particular situation. We know the problem was a restriction that caused it because we added it to the system, but these are just the things you're looking for in order to prevent compressor overheating all right, so i'm brian with hvac school, i'm eric from hvac school, we'll catch you on The next one, thanks for watching our video, if you enjoyed it and got something out of it, if you wouldn't mind, hitting the thumbs up button to like the video subscribe to the channel and click, the notifications bell to be notified when new videos come out, hvac School is far more than a youtube channel. You can find out more by going to hvacrschool.com, which is our website and hub for all of our content, including tech tips, videos, podcasts and so much more.

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