Hey thanks for watching this is part one in a two-part series. We did a class at the calo's offices, with some of our techs and some of the apprentices installers on low voltage electrical basics, focusing on finding shorts and opens in various circuits, but in this first video it's really just a lecture for me kind of prepping. The conversation attempting to get some of the basic language right in order to make our time diagnosing hands-on a little bit more productive hope you enjoy all right. So today we're going to talk about electrical diagnosis and specifically we're going to focus on low voltage electrical diagnosis, because that's the area that most technicians say they struggle with.

If you pull any group of kind of junior to mid-career technicians, low voltage, diagnosis and electrical diagnosis in general are um are the things that people struggle with the most along with diagrams schematics those sorts of things um. I actually want to start with a comment that i got on youtube. The other day i think, was on youtube. Maybe it was on on the website, but somebody said that they wanted more training on how to diagnose circuit boards and wanted to know more about circuit boards.

And i that's a good place to start, because it represents a black box that people don't understand. And so what they want. Somebody like me to do is to explain how circuit boards work generally, but there's a problem with that. What's the problem, uh each circuit board is designed to do something different yeah.

Each circuit board is designed to do something different. So, in order to teach somebody about circuit boards, you would be teaching them about electronics right. That would be the only thing that you could talk about. That would be general enough.

That would have any meaning, but do we fix or repair circuit boards in the field? No answer is no, we don't so i can teach people in the field how to um repair and understand circuit boards, and that would waste a lot of their time. Now. It's not to say that that's not a valuable profession, but that's not the profession that we're in. So what do we really need to know about circuit boards? We need to know inputs and outputs right and that's what everyone says, and somebody said that you know i'm frustrated.

I want more than just inputs and outputs. Well, that's what you have to understand and then you have to understand sequence of operations. So, in order to understand a circuit board, you have to understand what is that circuit board designed to do if you don't understand what it's designed to do? If you don't start there, then everything else you know about you know resistors and capacitors, and everything else is pointless. It doesn't mean anything knowing that doesn't help.

You fix air conditioner, so i want to start there quickly and just review um specifically. What we're talking about is residential air conditioning and heat pumps. We focus mostly on heat pumps, that's where we spend most of our time and that works anyway, because the low voltage electrical tends to be a little bit more complicated on them. So you have to understand the basic circuits within those systems.

Now, that's not what this video is about. It's not what this class is about specifically, but you have to start by understanding what r is. What c is what w is? What y is what g is and those are just terminal designations? People will often say you know what color wire should go to it. Well, electricity is colorblind.

Electricity does not care what color the wire is, but it does matter that the start of this circuit being on this conductor on this end ends up on the right place. On the other end, and so a lot of what we're doing is making sure that we're connecting things in the right places. So they go to the right spots and in terms of an installer's responsibility in terms of the service technician's responsibility. So much of what we do comes down to that you know i think ductless systems they talk about how like i'm making this up, but i think i heard this at one point: seventy percent of the problems the ductless systems have to do with the electrical wiring Being done incorrectly, you know crossing wires or not making good connections all the time.

Those are the sorts of problems that we run into and a lot of the issues that we run into in the field, specifically with low voltage diagnosis, start with really really obvious and simple practices that we have to get right. But let's start with a couple things: sequence of operation, just some things that you need to know about a piece of equipment. So let's talk about the difference between a straight cool system and a heat pump system. Juxtaposition so start with why? Why the yet what we would commonly call the yellow circuit, even though it doesn't matter what color the wire is, but it's the y circuit.

What is the y circuit? Somebody in the audience is: okay, it doesn't you don't have to have a mic. I have a mic. Okay, so so eli said contactor. What else would a lot of people say the? Why circuit is they say it's a compressor.

What else they would say it's cooling right and so is it all of those things? Yes, is it more than those things could be right, so you have to know what we're saying we say why we could have a two-stage system. We could have y1 and y2. Let's use that as an example quickly, y1 and y2. What do you need in order for a two-stage residential piece of equipment to run at full capacity in terms of your terminal designations? What do you need to energize y1 and y2, y1 and y2 right? So a lot of people? If you don't know that you would think well, you'd have y one that's stage one, and then you go to y two, that's stage two right, but it's actually y one plus y two equals your high stage, your full capacity operation right.

So it's things like that. You got ta start with knowing that about your equipment. What are each one, what are each of these terminal designations, for when should they be activated that sort of thing um, when we talked about cooling versus compressor versus contactor? All of those are true in one sense, but where's the problem with saying that. Why is the cooling call what's the problem with that heat pump application in a heat pump? It's your contactor right! It's it's! What specifically energizes the electromagnet on your contactor.

Let's grab a contactor here quickly. So what is why really well y energizes, our contactor coil, which is an electromagnet which then pulls in our contacts, which then allows our compressor and generally our condenser fan to run. So it's a much more complicated story than just saying it's cooling. Now, if this were a straight cool unit, typical gas furnace or a system that just has electric heat strips, that would be all that cooling would be you just energize that and your outdoor unit runs depending on how the system's set up.

You may also need a g call in order to run your blower, but that's that's basically it, but on a heat pump. Why isn't this cooling on a heat pump by itself? Because you have a reversing valve because you have a reversing valve tanner answered yeah. You have a reversing valve and the reversing valve does what switches? Yes, the reversing valve switches between cooling and heating, so the compressor contactor stays pulled in either way, whether you're in cooling or in heating, and then in order to run in cool mode. You energize, o.

We call it orange, but again that's just a color doesn't matter, but that's the o terminal. We energize o on most uh, most heat pumps. We work on in the cooling mode and that's what designates cooling, because that reversing valve switches into the cooling position. So there's a lot of things like this and again, like i said, i'm not gon na we're, not gon na go through every single circuit here.

But if you don't understand what each circuit does specifically on the piece of equipment, you're working on then start there start by memorizing that i know we don't like to memorize anymore, but for newer technicians, especially if you're thrown into the deep end. You don't have a lot of theory behind you, you don't have a lot of the basics. You haven't read the racked manual, you don't you haven't been to school, which is a lot of technicians nowadays, memorize two sets of things memorize your standard, four components of the refrigeration cycle, compressor, condenser metering device, evaporator your standard three lines, discharge line, liquid line, suction line And then memorize all of your standard circuits on the low voltage side, because those are things that you're going to interact with all the time. Those are very easy, but literally just memorize them memorize what they do in a heat pump, memorize what they do in a straight cool once you know that it's going to be a lot easier to understand what we're doing be a lot easier to teach you exactly.

It's going to be hard to teach if you don't have some of these basics. Memorized and honestly, when i went to school one of the best things my instructor ron kerry did. Was he sent me to the white board and he said all right. We're going to draw a compressor, condenser metering, device, evaporator and you're, going to do that over and over again and you're, going to mark them you're going to mark the lines you're going to write what's in each line and what each component does i'm going to erase It you're going to do it again, and i did that for the first couple days until i had it memorized.

So that's on the refrigeration side on the electrical circuit side. It's just what each one of those terminal designations does and as you go through and you memorize straight cool, that's easy, then go into heat pump, then go into multi-stage heat pump, then go into systems that have accessories like dehumidification. So, let's go over some of the standard, diagno diagnoses that you're going to make on low voltage and knowing the difference, because in terms of language using the right language to designate what you're doing or what you're finding or what you're. Looking for in the system.

If you don't get this straight, it's going to be really difficult for you to learn this. So, let's start by with a couple terms: the first one is short and we're going to define a short quickly. So let's do that eric? What is this short circuits? Your circuit's not going through an attended path, another another path that it shouldn't be exactly so it's taking an unintended path. So there is an unintended path that exists.

That shouldn't be there so the way that i've always said this and i can't think of a better way, something's happening that shouldn't be happening right. You have a path that shouldn't be there. It's taking a shortcut right, as we know we all know we're not supposed to take shortcuts and doing our work right. So that's what the electricity is doing is it's taking a shortcut, it's taking a path that it's not supposed to take, but that leads to the question: what path is it supposed to take right, so you got to know that what path is it supposed to take? So again, let's think about the y circuit.

Super simple y circuit goes to one side of the contactor. That's where it ends up, it may go through a wire. Nut may go through a terminal block may end up in a circuit board, but eventually it's going to end up on one side here right, but where does the other side go? So if the y circuit is ending up on one side of our electromagnetic coil? What's going on the other side common right, what does common mean? This is a really good one. This is a really important one.

Someone actually asked this today. What is common? What is it the other side of the circuit to complete it? Okay, that's a good answer. I like that, let's keep going with that. What is common common is a common point in a specific circuit, a common point in a specific circuit.

Okay, all right, you reuse the same word. I think. That's what we call cyclical thinking. That's fine go ahead.

Common is one side of the transformer and every other wire is the other side. Okay, one side of the transformer and every other wire is the other side, but let's think about it more generally, because common isn't just on transformers right, we say common all the time. So i started with these two, because these are the two two of the most misunderstood phrases electrically that get used. Okay, so let's start we're gon na go back to short and then we're gon na hit comment again short, is what happens when your grandma says the tv is not working right, my tv is acting.

All weird probably has a short must have a short that chord has a short in it and what is short, come to mean in modern day life, because we've all said it like before you started doing air conditioning work. You've said the word short before you've heard the word short before right, it's brendan is that right, brendan's new, so forgive me but brendan you've heard the term short before you started working on air conditioning right yeah, and how would you use it? How would you hear it used tv yeah something's, not worth it if your cars do acting up right, something's happening with the car? It's you know it's stalling out on either side. It must have a short. I think it has a short, but what people mean by a short is some random electrical problem that i don't understand, that's what they that's.

What short has come to mean, but a short is a very specific type of electrical problem, and so, when we say short, we need to know what we mean when we say short specifically with low voltage electrical problems. So let's back it back to that. What's generally going to happen when we have a short blown fuse blown fuse or tripped breaker on the transformer, sometimes the transformers will have a low voltage circuit breaker on the transformer and that's going to be tripped. It's going to be overloaded.

So why does a fuse blow? Why does a fuse blow voltage isn't going to the intended point? Okay, there's some truth there, but why does it what's what's the number listed on a fuse, you've all seen a fuse before right? What is that you've all seen a fuse before it has a number on it? What is that? What is that? What does that number mean amps? It is oh there's another word that we don't know what it means. That's that's a cool one. So, let's address that quickly, so what is amps electrical flow electrical flow? Okay, yeah yeah. It's doing work right, but what is it really? What makes it different than some other things that we measure like watts and volts? So we give a number to amps.

So point zero, zero one amp is electrical flow and a hundred amps is electrical flow. What makes them different from each other? What makes a hundred amps different one's a lot more one's a lot more right? Okay, i'm not! This isn't a trick, but it's more, but it's more of what it's more current, it's more electrons right, more electrons are moving. That's all right voltage is the pressure. How much pressure is there? An amperage is the amount of current right.

So when you have a three amp fuse or let's say a five amp fuse, that's the most common, you have a five amp fuse and that bad boy blows. She blows on you right what caused that too much amperage too much current too much flow above what number, if it says, five on it. What does that mean? It was over? It was above five right and in fact, if you were to run say six amps through a fuse, do you think it would blow right away? It would not, it would sit there for a while and then eventually it would probably boil it might not even blow. But eventually it probably would blow, but if you tried to run 100 amps through it, what would happen pop right away and what happens if you take a low voltage wire like your y wire or your red wire, something that's energized, an energized conductor and you touch It to ground what happens pop right instantaneously fuse blows right if you've done it.

Sometimes you see you've got to get a nice little arc fuse blows. Why does it blow quickly, based on what we just said, i'm bleeding down a path here. Why does it blow quickly way too much current right? There's too many electrons moving, and why are there too many electrons moving, because you created a path with no resistance, because you created a path with no resistance with very little resistance? Okay, so there's a couple other terms we got to know we got to know the term load, so the electromagnet on your contactor, the part that makes it pull in that's a load. It has resistance.

So, in order for a circuit not to blow a fuse in order for a circuit not to draw too much current, it has to go through its intended path and its intended path is through a load. It's also through a switch. It's also through certain wires and circuits, but it's through a load make sense. My nose, all of a sudden, is getting really itchy.

Take care of that you take care of that. I will i'm going to i'm going to just yeah there we go now. I feel better. Okay, maybe it's this super toxic contactor, that's right in front of my face all right, so when we have a blown fuse on a system when you walk up to a system, this is the installer's most dreaded moment.

We have a couple installers here. So i'm going to make fun of you: it's not your most dreaded moment anymore, really, okay, good good for you most installers. The most dreaded moment is when you fire up the unit and it and it doesn't run and you open it up, and it's got a blown fuse right right right. It's pretty dreaded even a lot of service.

Techs! Don't like that very much right. But what is so when you see that blown fuse? What do you know? Don't guess what do you know for a fact, sam at some point, some high current too much current through the fuse right? That's what you know there's too much current and what is the most likely cause of too much current a short, a short right and a short that bypassed a load. So it went straight from one side of the power supply to another. If we think of like a really basic circuit here, if you think of like the most basic circuit, we've got a battery and through that battery we have a switch.

And then it goes to we're just going to draw a really simple light bulb here and by really simple, i mean very poorly drawn light bulb. So this currently is drawn as an open circuit, because the switch is open, but let's go ahead and draw the switch closed. So now we have a path, we have a completed circuit and this circuit is not shorted as it is currently drawn, because the electrons have to move through the light bulb and so it'll light up. The light bulb right.

That light bulb adds what to the circuit resistance and that's resistance to the circuit. The resistance is what keeps the current down it pushes back against the current, and it keeps it from being too much. We have some great videos from ty branham and he's done some really great classes on just kind of describing that you know pushing people around in office chairs and that sort of thing you get the idea that if you don't have a force, pushing back against those Electrons moving, then you get too much electrons moving too much current and that leads to a blown fuse right. So that's what you know for sure when you got a blown fuse, something caused the current to be too high and most likely it's some version of this.

So this guy right here is a short. You got a path, that's not supposed to be there, it's bypassing the resistance and it's making the fuse blow right too much current. So that's what a short is. It's very specific, now there's a different kind of short, and you need to know this because, as we do these classes and we're going to do a lot of them on these trainers, this is a hands-on class and we're going to get there pretty quick.

As we work on these trainers, there's a different kind of short that doesn't involve a blown fuse and some people will argue that it's not a short, but i still think it is, and what is that? What is that different kind of short if you have two wires that are rubbed out connecting each other touching, where they're not supposed to be there's a lot of innuendo in there, but we're gon na we're gon na just pass by it. I'm just gon na ignore it we're gon na pretend like it didn't happen, but they are on the hot side of the circuit they're, on what we call the switch leg. So most most of what we're working on in terms of our circuits are in between our switch and our load, so that would be things like y. That would be things like o.

That would be things like g. That would be things like w. Those are all standard circuits that are in between the switch, which is what, by the way, what is the primary switch in a typical air? Conditioner thermostat is a switch right. It's a traffic cop, it's the one saying who goes where what turns on what turns off? In the right order, but most of these circuits are in between our switch and our load, our load is whatever they're.

Turning on and off your reversing valve your contactor, your blower relay your heat relay or gas furnace, whatever it is right, they're, turning something on and off, but what happens if those two touch each other, that's what we would call a switch leg short, that's a term! I completely made up, but it's the best one i can come up with where there's an unintended path and the result is not a blown fuse, because you don't have too much current. It's not bypassing. It's not bypassing the load like this one is it's just bypassing the switches. The switches are getting mixed up the circuits that are past the switches and that's resulting in things running when they shouldn't be running mostly.

So that would result in things like if your white wire, for example, on a heat pump crosses with your o wire, your orange wire. What would happen? I'm just going to ask that as a question. What would happen if you mix together, white and orange and those two touch heat strips, would come on in cooling, interesting, but what else would happen? Cooling would come on whenever the heat strips right, because those two circuits would be completely crossed, so heat trips would come on with cooling. Cooling would come on with the heat strips meaning.

Reversing valve would be energized in this case because the heat pump, those two circuits are crossed. So that's a type of a short and often like when we talk about things going haywire in our car or whatever that's a lot of times what's happening. You have circuits that are mixing that shouldn't be mixing they're connecting that shouldn't be connecting it's not necessarily always bypassing the load, bypassing the resistance which results in a blown fuse. Okay, so that's important to know.

We got some clarity on what a short is unintended path. All right, what is common common, basically just means a place where you connect things together. That's really what it means, because think about a comment on a capacitor, the c terminal on a capacitor that has nothing to do with the common side, on the compressor. The c terminal and compressor they're on opposite sides of the circuit, but they're both called common, but in a capacitor, it's the common point between two capacitors.

So it's a point where they're connected together in on your compressor, for example, common the common terminal on your compressor. What is that? It's a common point between the two windings common point between the two windings? Exactly you don't have a common winding. You have a common point between two windings run and start connect together common on a low voltage circuit. What is common, jessica, low voltage circuit? What is common, you know it's the other side of the 24, but where does it end at? Where is? Where is the ultimate point where common connects kind of it can? But it's actually the transformer it's the other side from hot, on the secondary side of the transformer right.

So that's where the 24 volts comes from one side is common, one side is hot. Now often common is grounded, they dedicate common to ground in order to make diagnosis easier and everything a heck of a lot less confusing, and we're not going to talk about that right now. What happens if you don't ground it, but that's what common is common just means a point where things connect together and if you think that common is a universal term, then you're going to connect things where they shouldn't go. It only takes connecting you know your common wire on your level to side to the c terminal and the capacitor once to realize that it makes fire and stuff okay cool.

So the next term that we need to all get straight and is really important to distinguish from short, is an open. What is an open, a break in a path, incomplete path, breaking a path it could be designed or undesigned, so a switch opens and closes the circuit so open. Is the juxtaposition the opposite of closed right now? The problem is, is that people get confused with this and, and you know like you - can make fun of it because we've always those of us who've done this a long time have always known this. But what happens when you open a faucet? You get water, you get flow.

What happens when you open a switch, no flow, no flow right. So it's the opposite. What happens when you open a door? You can walk through it. What happens when you close the door? You can't well, it's the opposite.

So the best way to think of open and close is opening and closing a drawbridge. That's the best way i've come up with when the drawbridge is open. The cars can't pass across now the boats can so you know that makes it kind of ruins, even that one i've heard that yeah that's true seriously. Evil knievel that bad boy, his leaper but open means a break in the path that could be designed like that.

But it could also be if i take the wire, if i take this wire going to my float, switch right now and i cut it, that's an open right. If the water rises in the float switch and it trips the float, it rises the flow. What does that do to the circuit opens? It opens the circuit right. So what happens when a circuit is open? What happens to the system electricity stops flowing through the component electricity stops flowing to whatever circuit we're talking about? So if there's an open in the y circuit back to the old ubiquitous y circuit, what's going to happen, compressor contactor is not going to pull in compressor.

Contactor doesn't pull in. That means that your condenser fan and your compressor is not running right. So pretty simple. If your float switch opens it's going to generally, we wire it to break r, which is our main 24 volt power, so everything's going to shut off, except maybe the blower time delay that that's one that always confuses people right, you trip it and then it just Keeps running for a while, what's going on it's magic anyway, so that's what an open is.

So here's what i don't want you to do as we're going through this, because we're about to get hands on here about to get handsy on these things. I don't want you to confuse open and short. So if i ask you what's going on with this system, don't automatically say one or the other think through. If it's a short, then something's going to be happening that shouldn't be happening either a fuse blowing or circuits cross, where one thing's running when it shouldn't be running it's not time, it's not the right.

It's not in the right order right. Those would be a short, whereas an open would be nothing's happening on a certain circuit or with the whole system. Right make sense all right cool any questions about what we've covered here so far, so you'll notice a couple things we didn't cover, because this is only a two-hour class actually a little less than two hours, because some of you don't know not naming names but uh. We're not covering schematics we're not covering you know, identifying components or any of those those are for different classes, but today's class is specifically diagnosis, but i wanted to get some of these terms straight.

First, let's talk quickly about the meter for any of you who are new to the meter. The first thing i always want to see you do before you use a meter. This is just a really good habit to get to get in. The habit of doing is.

Take your meter and put it on where, where should we put it first before you use it ohm scale, because what is a meter doing when you put it in ohm scale, sending out voltage on the leads sending out current right? So there's a potential across these two leads that means voltage between them. It's not much! It's not going to shock you right, but there is some voltage at the tips of these leads and what is it looking for looking for a path right now, don't pay too much attention to that ringer, because different meters have different ohm levels at which the ringer Will go on and off so look at what it's actually telling you if i put them together, what what's my readout here: zero zero, very near zero right! That means that my leads are intact, because i wouldn't want to start trying to test me like i'm. Not getting anything right also be really careful with the term uh. No, i'm getting no ohms or i don't have any ohms.

I don't have any i'm not getting any, because that could mean that i have a perfect path right, because could you say right now that i'm get that i have no ohms? I could say i don't have any ohms right, and that means that i have a near perfect path. There's almost no resistance, but i could also say see right now. What is it? What's? A screen show just a series of dashes, so i could say right now: i've got no ohms, i'm not getting any ohms. So what is the right term? Infinite, ohms, zero, ohms or near zero ohms right.

So zero in this case means no resistance or almost no resistance, and this when they're not connecting - and there is no path - means infinite right, open path. So that's another way to think of this closed open. But what about? Why am i doing this again before? I start testing anything else, make sure my meter, and my leads right now - is that the best way to check no the best way to check would be to put it on the volt scale and then actually measure on a known power supply so actually take it, And plug it in to an outlet and see what am i getting so now we have 120 volts. So that's a better way, because now i'm actually checking to see that my if i'm measuring voltage that my voltmeter is actually working cool.

So i want you to do that. First, if you're working on any live circuits, you need to be wearing safety, glasses, okay, so get those. I know we got extras. Mario can hook you up with some.

If you don't have any, so definitely be doing that 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. You can also subscribe to the podcast on any podcast app of your choosing. You can also join our facebook group if you want to weigh in on the conversation yourself thanks again for watching.