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In this live stream, Bryan walks through electrical diagrams and teaches his apprentices how to use schematics for circuit tracing. Ladder schematics are the most common type of diagram you will see; those and connection diagrams are what we mostly use in circuit tracing.
There are five main types of diagrams: ladder (schematic), point-to-point (connection), pictorial, shop drawings, and as-built diagrams.
Ladder schematics are basic and include common symbols to indicate pressure switches, contacts, power supplies, loads, etc., that illustrate how equipment is wired. They are NOT accurate visual representations of the components. Ladder diagrams connect circuits from one side to another (such as L1 to L2, hot to common, etc.). In the HVAC industry, we usually work with parallel circuits, which make up the majority of the ladder diagrams we see. Series circuits may occasionally appear, but they are much less prevalent than parallel circuits. (Safeties are series of switches; they are NOT series circuits.)
Point-to-point or connection diagrams are becoming increasingly common. They do not illustrate clear sides of the circuit, but they show you each conductor and where those conductors go. You can trace the diagrams relatively easily, so you can tell which components are connected. You can also tell which components are optional and learn more about the physical features of the equipment; you cannot do either of those effectively with most ladder diagrams.
Pictorial diagrams illustrate circuits with visual representations of their components instead of mere lines and symbols. (Motors look like motors, not series of lines and circles.) They are uncommon because they are difficult to draw. However, pictorial diagrams illustrate the connections and the real components very well and are quite easy to work with.
As-built drawings illustrate the equipment as it is built. Other schematics, especially point-to-point diagrams, illustrate optional components. Crankcase heaters are common optional components that you would see on a point-to-point diagram but not an as-built one. Therefore, component identification is a major skill for reading all types of schematics.
Bryan also covers some common symbols on diagrams. One common symbol is a bell (pressure switch). Pressure switches remain closed until a pressure change opens them. Most safeties are single-pole, single-throw. Contacts show up as gaps on schematic diagrams. A normally open contact will be a mere gap, and a normally closed switch has a slash through the gap. Little circles usually represent relay coils, but squiggly lines may also represent relay coils. A capacitor is represented by a gap with one straight line and one curved line on each side of the gap. Arrows indicate time delay circuits.
When it comes to learning schematics, a good exercise is to take apart scrap units and rewire them from scratch with help from the schematic. Learning schematics takes time, patience, and lots of repetition with various equipment.
Remember, always read the manual, check the notes, and refer to the legend!
Read all the tech tips, take the quizzes, and find our handy calculators at https://www.hvacrschool.com/.


All right so we're going to be talking about electrical diagrams and circuit tracing which what i'm going to try to do is connect together. How we use diagrams and schematics in real life go over some different types of diagrams and schematics and then show some images. That kind of you know show how you translate, because i think that's where a lot of texts get stuck is you know they can look at a schematic and they can understand some of it. They can look at what's on the equipment and understand some of it, but it's taking the schematic and translating it to the equipment or the equipment and translating it to the schematic and so we're going to we're going to cover that.

So as we go, any questions ask uh apprentices. You can ask in chat or you can also unmute yourself and ask i encourage that because we got two hours here. That's a lot of time to cover this. For those of you who are on the live stream.

It is two hours, but we want a lot of interaction which will help us um help us come up with some uh content. That will be helpful to you. So here we go all right. First off there's several different types of um, schematics or diagrams that you're going to run into, in fact in different segments of the industry.

It gets kind of um confusing when you even say schematic or diagram like when i i asked my brother if he would come on and join us which he hasn't yet but um when you say uh schematic that could mean or even a diagram. That could mean anything from shop drawings, uh. It wouldn't necessarily always be electrical, but when we're talking about schematics and diagrams, these are going to be the most common types. The first is going to be the latter schematic, which is the one that's probably best for actually tracing circuits and we'll go over, that that's sort of the traditional schematic, the point-to-point or connection diagram.

That's actually becoming the most popular type that you're going to see on a lot of hvac equipment um. It has a lot more detail in it. It's also going to kind of show where the connection points are in real life. It's not a truly representative picture, so it still shows things like symbols to represent things, but it tries to make the connections a little bit easier and also a little more realistic, because on the ladder diagram, it shows how it connects electrically, but it doesn't necessarily show You how it looks when it's connected um and then the pictorial diagram, or i think, that's how you say that pictorial um diagram is more of a picture.

It actually looks like what the components look like so on a point-to-pointer connection. It might look it's kind of like what the components look like, but it's generally still going to use symbols with pictorial you're going to actually have pictures that look like the uh. The thing you're connecting so we'll show examples of that. Um you're also going to have things like shop drawings, um that often fall into the the term schematics or diagrams, which generally aren't specifically electrical.


These are going to be things that um kind of go along with plants and specs on jobs, or you know, pictures of equipment that go along with product data or installation, instructions that sort of thing and then you're also going to have which it could be. Any of these you're going to have as built and there's a there's a difference between a lot of the latter and point-to-point diagrams that you're going to see in the field and true as built and we're going to talk about that. How often a factory is going to give you a diagram that includes every possible option, but a lot of that stuff's not actually going to be there, where an as built is going to give you exactly as it was built, not something. That's uh.

You know a theoretical how it could be built, it's much more specific, so a lot of times um you run into uh, diagrams or uh or schematics that have all kinds of stuff in there that doesn't apply, and really the first thing that you're gon na do Is figure out what is really there and what isn't uh, and so, if you have an as built that that saves you a lot of a lot of heartache, but most cases we don't have that on the topic. While we're talking about as built, because this doesn't happen as often as it could as builds, can be drawn in the field, so if you, for example, you make a field modification to a system or you add on an accessory um, you can actually draw your own Uh, your own schematic or your own connection diagram in order to illustrate how it actually is, and that's really handy, especially if you're doing anything, that's you know, especially abnormal or especially strange. I know eric melly always always does that tries to find uh. I don't know why i said, tries to find he he takes time to um to go through and actually redraw schematics wherever applicable.

If he's made a made a significant change, uh one of the questions is: how long do these run um they vary. Uh. Last week's was an hour; it really just depends on what my schedule allows the vassal on tuesday these go on tuesdays and thursdays. This one is going to be two hours from six to eight all right.

I show this one here, uh this really basic ladder schematic because it is so basic and it just gives you a sense of a couple really common symbols that you're gon na see um and in a ladder schematic we're connecting circuits between uh one side and the Other side, in this case it's l1 and l2 um. So in this because it's 120 volts, that's going to be what we would typically call hot and neutral um. If it was 24 volts, it could just be between what we you know. We call hot and common, really doesn't matter what we call it we're going from one side of the circuit to the other.

Now, because this is a step down transformer step down from 480 volts ac to 120 volts ac, you can see that we have more wraps on this side of the transformer and fewer on the other side. This is the iron core, so this then becomes our circuit between l1 and l2. This is our power supply here it goes through. Here.


We've got a fuse, then it goes through a switch. We have a a coil in this case, which is you can see this m1 marking ties together with this m1 and you're, going to see this a lot you're going to see many cases where you have an electromagnetic coil or some sort of control. That has the same symbol as the thing it's controlling now often they're going to be separated. So you know everything.

That's going to be on the 40 volt side is going to be up here and here we're showing that it's using a 120 volt coil to energize. In 120 volt motor, but in many cases the coil or whatever you're, using to turn something on and off, is going to be on the opposite side of the circuit. So maybe the motor would be up here on the 40 volt side and the contact that controls. The motor would be up here, but when we energize this coil, it then closes this switch.

So, let's, let's uh talk through some um some standard infrastructure. First circuit, you first have to have obviously power supply. In this case we have a fuse. You don't have to have that, but you generally are going to have some sort of user.

Breaker you've got a switch. This is what we call a single pole. Single throw switch. The easiest way to think of the pole is the pole is actually the the part that moves there's only one of these, and it only throws in one direction.

So there's not another throw up here, so it only goes on or off. Then we have our load here, which this is going to be our control load. So this control load is controlling this switch. So when we flip this toggle, it makes a circuit from one side to the other which energizes this coil closes.

This switch. So what it would look like is if you took a a line and you slashed through it, like that, that would be a symbol for closing a switch now. This is showing its normal position, so this is a normally open contact. A contact is just a type of switch, that's controlled from somewhere else, so it's a contact that then closes and then energizes.

The motor somebody here uh brings up. Uh is talking about high voltage and low voltage series and parallel. Almost everything that we work on is parallel circuits um. We can connect switches in series with each other, so we could have a switch and a switch and a switch and a switch, but we're almost never going to put more than one load, which is the part that actually does work, whether it's electromagnetic, which is what We call inductive or whether it creates heat or light, which is what we call resistive, so both of these are actually electromagnets.

This is an electromagnetic coil that causes this contact to close similar to a relay or a contactor, and this is a motor and motors are basically electromagnets rotating electromagnets, so these are both inductive loads wired in two parallel circuits. So these are not series um very rarely. Are we going to use series circuits and and much of what we do? It's not in electronics, you're, going to see some series circuits, but in general a series circuit is referring specifically to loads in series, not switches in series. So a lot of people will say you know daisy chain switches together, like in a safety circuit.


That may be a series of switches, but that is not a series circuit. A series circuit is when you have more than one load in the same path in between l1 and l2. If that makes sense so yeah somebody else is commenting safeties or series again. That's a series of switches: that's not a series circuit when people say a series circuit, they're talking about loads in series, and this just goes back to i mean again, a lot of these terms are confusing and redundant and all that.

But if you, you know, go to the basics of electricity and they say a series circuit they're, not talking about a series of switches, they're talking about loads connected one you know into one and out of the other. That would be like your old school um christmas lights. You know where one blows out and they all they all stop working. We almost never have that any time we have a load, it's going to be on its own circuit.

It may have multiple switches to control it, but there's going to be only one load per path and i keep restating that because it is, it is an area where a lot of people um get very confused. So another thing here, uh to because again we're just talking about the different types of um, diagrams and schematics before we actually go into some specifics. So if this is really boring to you hold on we're going to actually look at some real life examples. But i want to set the stage here um, so, in the case of a ladder schematic there, none of this actually represents where the connections really are.

I mean these can be done on terminal blocks. These could be done on jumpers. These could be, you know, all kinds of different things that are making these connections and you really uh. This picture doesn't tell you what the components look like.

It doesn't tell you how they're connected um there's really nothing here, that's telling you how it actually looks in real life. It's just telling you how it's wired right. So i mean this could be a connection at a wire. Not it could be at a con.

You know a log, you know you just don't know it could be on a board, we don't know the ladder schematic doesn't tell us. The ladder schematic just tells us how it's wired so that we can understand how the circuits are laid out, and it makes it easy for us to kind of get a sense of what the circuit does, what it controls, how to trace it, how to diagnose it. Um to some degree, but when you're going to get really specific, you know this isn't showing us the color of this wire, it's not showing us where it's landed any of those sorts of things. So that's the challenge with a ladder schematic, but the nice thing is it's very clean and clear and you can easily figure out okay.


This is one circuit. This is another circuit and figure out what each one does. If you have any questions about that, as we go, feel free to uh feel free to unmute yourself, students raise your hands online, feel free to ask any questions that you may have or comments all right. So now we have a point-to-point diagram, we're actually going to go over this specific diagram a little further on, and these are much more common nowadays.

You can call them point to point. You can call it a connection diagram. Different manufacturers call them different things. Different books call them different things, but this is typically what you're going to see nowadays and you're going to notice.

This isn't laid out with a clear l1 and l2 on either side. It's really just showing you each conductor and where it goes essentially now you can figure out. You know again, we have our l1 and l2 coming in here from the power company, and so we can kind of trace it out. But it isn't this clear from one side through to the other.

If i wanted to try to figure out everything that was in this compressor circuit, for example, i would have to i'd, have to look through and and trace back okay. This is going through to my plus one pole on my contactor. Okay, that's going to l1! My start is going to herm on my capacitor. You follow what i'm saying so in terms of figuring out where things go in real life.

These are very nice. These point-to-pointer connection diagrams they're, going to have a lot more detail. So they're generally going to tell you things like you know, what's optional and not optional um, it's going to tell you the colors of the different wires, sometimes especially on a larger commercial ones. There's going to be all kinds of numbers all over it that allow you to kind of reference um.

You know the a number marker on that particular conductor or wire um. So those are those are some of the advantages here, but they are a little more challenging to kind of figure out how everything is wired because it takes a lot of you know, traveling all over the place, all over the picture in order to figure out your Circuits and then we have our pictorial and - and this is just an example of a pictorial um that i grabbed um that actually shows you know the motor looks like a motor. The overload looks like an overload. A contactor transformer looks like a transformer switch fuses.

All that and then over here we've got a ladder schematic, so it kind of these two relate to each other um, and actually this isn't really even a true ladder schematic because you've got. I mean it is a form of a ladder schematic, but it's not going. You know a ladder across um and so the pictorials are nice. We don't get a lot of those because it's very difficult to draw super complicated circuitry with drawing a picture for everything, but sometimes with simpler things.


We will have pictorials and that's very nice, because it not only gives you the connections but instead of using symbols, we're actually drawing the components the way that they actually look. That's what makes a pictorial a pictorial is that you're, drawing the components how they actually look. So it assists with identification of the components. So that's a that's a key element of of pictorial, all right so now, and i'm gon na move some things in my screen.

So that way i can access everything here. Um now we're gon na go over some individual circuits. Let me see if i can zoom here yeah i can okay and um. This is a a very basic single phase: ream unit, i'm releasing a video on sunday about this unit, just kind of going through the individual components, but i want to show you um how you would do this, and this is you know almost about as simple as It gets in terms of a residential air conditioning system, but there's some things that create some overwhelm for newer attacks when they get um.

You know when they first start using schematics uh, and i want to try to help eliminate some of those challenges. So the first thing is is that when you're looking at this picture, some people will kind of take this and this and put them together. But these are actually two schematics of the same thing, and a lot of manufacturers are doing this nowadays, where they're, giving you a ladder schematic a true wiring schematic type and that's what this is and then they're also giving you the diagram, which is more of a Point-To-Point or a connection diagram, but you see they're just calling this a diagram and they're calling this a schematic. So not all manufacturers use the same language and if you look in your book, it's going to uh it's going to talk about this being a point-to-point or a connection diagram and this being a ladder.

But here they don't say that they just say schematic and wiring diagram jessica's supporting her blue on hat. She she went over to the dark side, it's good good to see that jessica um. So here's where i would always suggest, starting when you're looking at a at a diagram like this or a schematic like this start by and again this is this - is true of a lot of uh a lot more of your residential type equipment um. If you're just trying to get a sense of what you've, what you've got, first identify what is optional and what is standard and there's a lot of things on this that are optional.

So, let's go through and just pick those out. So here we have a start relay so this is your potential relay. You can see here, it says, opt optional. Now, how do i know it's a start relay because it says sr.


If i don't know what something is i go down here to the component code? You can call that the legend or the key go down and see what it says. So, let's zoom in here a little bit. It's not the best uh, not the best picture, but sr stands for start relay. It doesn't say what type of start relay, but we know it's a it's got 521 listed on it, and that is a potential relay.

We also have this sc, that's optional. Well, what is that? What is our sc? You can probably guess, but that is a start. Capacitor also optional, so when we look in this unit, we have to identify, does it have this start relay? Does it have the start capacitor in this case this unit? Doesn't these are uh options for the unit? So oh they're they're, not there um we're going to go over to some of our safeties. Oh actually, let's, let's first do our crankcase heater, so we've got cch, which is crankcase heater, crankcase, heater, optional, chc, crankcase, thermostat or crankcase crankcase heater control.

I should say optional. Hgs hot gas sensor, optional, lpc, low pressure, control, optional lac - i mean you're getting the point here, but if you were trying to pay attention to all this stuff and tracing it out, you would find really quickly that it's just going to gum up the works because You're looking for all this optional stuff, that's not there so make sure that you know what is there and what isn't there? Even this tb is optional. What's a tb tv is a terminal block which means that there's a good chance, this terminal block ain't going to be there. That's really going to confuse you if you're expecting to see a terminal block and then it's not there, because what do we have here? We've got these, we've got these wires and these reference back to notes here.

So this one here goes to note number five to thermostat sub bass refer to system schematics or schematics for indoor section for low voltage control wiring. So it's saying this is field installed. Low voltage circuit to be any c class whatever you know, so it gives you these little references for each one of these, but these are field wired. This is your um y and your brown that that's coming from the field that you're going to connect here.

We've got dashed lines dash lines, it's going to tell you what dashed lines are factory standard is a solid line. Factory option is dash, dot dash and then field installed is dashed. So these are field installed right here, and these are your high voltage conductors. These are factory options, we got our ground here.

We got our l1 and l2, and here it's going to even show you that on uh on your yellow and your brown, those are also field installed. I wish that these these really should be dash too, because these are field and salt. These are your low voltage conductors that are coming in from your, in this case, they're feeding from your air handler, but they're, ultimately coming from your thermostat. So why is your y circuit powering your contactor brown? Is your common? If you don't know what these mean well sure enough, it's got a wire color code, too: yellow white red purple orange black brown, blue, green gray right.


So you see the first places i'm starting. If i want to understand a piece of equipment, a lot of stuff here down the bottom in your legend or your key, looking at your notes, getting used to your components, identifying your components, color codes, what the different symbols mean, what the different um you know, wiring Dashes dots, solid and all that what that all means getting a sense of that now, a lot of this stuff is pretty universal, so once you get used to it on one, it's going to be the same on many others, but it isn't always going to be The same thing here, that's interesting about this diagram that you're not always going to see is it actually shows wire nuts things that need to be wire nutted together, so there's going to be a wire nut between this factory wire and then this factory option wire. That's going to go to your cc, your compressor, contactor, here's! The next thing. I want to show you're going to notice that here it tells you where things are optional over here it doesn't.

It doesn't show you what's optional over here now it's got some numbers still. So you can kind of identify some of your connection points but, for example, if you look at your outdoor fan motor just as an example here you're going to notice, it doesn't tell you colors, it doesn't tell you common start and run. It doesn't tell you much of anything, so you know that one of the terminals on the outdoor fan motor has to connect to f or fan on the run capacitor, but you don't even know which one over here it doesn't have as much detail. Now.

It's much cleaner, so it's easier to trace your circuits through, but it lacks a lot of the detail. If we wanted to know more about this, we would have to go over to our outdoor fan motor and then we would see okay, there's a black wire. That goes through here and then ends up going back to t1. Now, even this is interesting, because what happens, if you don't have all of this additional factory stuff, so you don't have your lac your low ambient control.

Well, in that case, then, this black wire is going to nix all of this, and it's just going to go straight from here to the top of your compressor contactor. Now that's kind of annoying because it doesn't really like you have to you have to figure that out like it's, not that's not obvious. It doesn't tell you that, but because these are all optional, just imagine that these are all deleted. What do you have left? Well, you have this black wire.

If it can't go to this because it's optional well, then, where is it going to go? Well, it's going to go where it ended up, which is up here on t1 top side of your contactor right, which is in fact where it is on this unit. So a lot of the stuff that makes these complicated is that these are not as built drawings. So back to what we're talking about before and as built would be. This is exactly how this unit is in real life, but because the manufacturer has to draw one and it has to cover a wide range of factory options.


They've got all this additional stuff in here that you have to delete out in order to make sense of what you actually have in the field. So you have to know what you got, what you don't got, which means that you actually have to start by looking at the equipment, because there's nothing on there. That's going to tell you what is in that or not we'll use the example of the crankcase heater. If you don't know what a crankcase heater looks like, then you're not going to know if it has this cch option, so a big part of being able to read schematics, the big part of being able to trace circuits is component identification because if you see again, Cch you're going to assume oh well, you know where is this circuit well you're, looking for a crankcase heater you're, looking for a belly band right, you're! Looking for uh, you know one of those insertion type um crankcase heaters.

If you don't have that, then you say: okay, this is a factory option that doesn't exist, delete. I can't find any of those those options aren't going to exist. Right makes sense. Let's take a look.

If we have any questions performance hvacr says you can usually see. Most of the components when you open the control panel um - that is often the case, but sometimes it's not and again it depends on what we're talking about here. So this is a residential unit. So yeah, you can easily see everything you know by looking down at the top and looking in your control panel, pretty straightforward, but if this were a commercial unit that had multiple panels in it uh, then it's going to be a little more difficult.

You're going to have to go through everything and there's so much there that this is where a lot of people get overwhelmed, so i'm just kind of starting with uh some of the things that i like to begin with. So that way, you're not so distracted again. What components do you have? You know no one kind of looking at all the stuff in your legend or key, eliminating all of the factory options that you don't have so you're, not looking at those and now you can begin to look at one circuit at a time, because when you're diagnosing You're always going to be focusing on one circuit at a time. So let's say we have an issue with our um.

I don't know. Let's say we have an issue with our compressor, for example, so we can go over here to our more basic diagram and we're going to look at what's in the compressor circuit. This is a nice place to start because it's kind of it's kind of stripped down right, so we can see that we've got our compressor contactor. Now this is your typical single pole or what they call a one plus contactor.


It's got one contact in between l. This this says l3 and t3 um and then l1 and t1, but this is literally just a hunk of metal right, so our common for our compressor is connected straight to the line. Now, if we want to look at our note, if we want to be real thorough, which we should be up here, it has three. So, let's just see, if there's anything connected field, wiring and grounded rain, tight conduit diffuse disconnect all right.

You know not not real specific to what we're talking about here, but it's got a you know, so that would be something to check comes through goes to our common okay in order to make the circuit in order to get to the other side, though, we've got These two other circuits, let's start with run so that's r, goes over to our other side and connects to our t3. Now, where does it connect? Well, it's showing just sort of like middle of the ladder. If i want to know exactly where it connected, then i would have to go over here. I can see all right r trace that down.

Okay, that does connect directly to the t3, but see again, you wouldn't know that, because this doesn't show that it's connecting directly to t3. It just shows like here that could be a wire not for all. I know right because this diagram isn't concerned with specifically how it's connected it's concerned with electrically how it's connected, because electrically everything that's along this line is the same right electrically. There shouldn't be any significant resistance, so these should all be the identical point, but only when you come over here and you pay attention to where it's connecting do.

You know exactly where that point is, which is why they call it a connection, diagram or a point to point point to point connection to connection and then, in addition, we know. Okay, this is going to be a red wire, but starting over here is kind of nice because it's a little simpler right. So we see that this cc contact is what's going to open or close to energize or de-energize. This compressor, that's pretty clear.

That's the only thing that's in the way of running this compressor is this cc contact now we're all bright enough and we've seen enough systems that we already know this right. It's a compressor contactor. So some of you are like okay, ryan. This is boring.

Why are you telling me this? Because this is the basics on which you build in order to understand much more complicated, schematics and diagrams? And this is what the mistake that i think a lot of texts make i'm going to just wax. I guess not poetic, but something for a second texts jump into complicated, schematics and diagrams, because they don't need schematics or diagrams on simpler units. You can see it all. You know all the components.

So why do you need a schematic right and so you're not used to looking at them? Then you end up on the big munters unit or the big aon unit, or you know the humidimizer or whatever you're working on that's weird and now you start trying to read this big complicated schematic and you get overwhelmed. The key to not be overwhelmed is to understand everything. That's in them, eliminate, what's not there and then focus in one circuit at a time based on what's happening. So if we were having a compressor issue, this is where i would start just understanding everything.


Then we go over here we say: okay, we got our start terminal now. Where does that connect? Well, if i didn't know better, i would look and say well. It goes up here to the 2 terminal between my start relay and my start capacitor. Well, because here it doesn't say that it's optional, but i, if i, if i paid attention to that i'd, be like nope.

This is all mixed. This is out so this doesn't exist. This wire doesn't exist. Forget this.

I've just got this and then it go this wire here and it goes to h or herm on my rc, which is my run capacitor right, let's go over here now. I can actually see a little bit more information. It is a purple wire that goes from s to the herm terminal on my run capacitor. So i have a compressor problem.

I might want to check my run capacitor. Where am i going to look right? Run? Capacitor compressor contactor. Those are the two things i want to. I want to pay attention to.

Is my switch closed or is it open? Is my capacitor open or is it? Is it measuring the proper microfarads? So these are things we already know because we have this memorized but say you didn't know much about it, but you knew how to read a diagram and you had a compressor problem. You would know these are the things external to the compressor that can affect those circuits make sense any questions so far: uh, okay, uh. So a couple other things. So if we look here, we got our lac.

What's our lac go over here low ambient cooling control? Now something i want to focus on real quick, because this doesn't explain what symbols mean. You got to know some basic symbols and we've done this a lot in the class already. But i want to go through now and take a look at some of these symbols and some of these switches and the picture isn't real good here, but they often aren't. They often are kind of small and hard to see so lac.

This is basically a fan. Cycling switch is what it is, but it's a single pole single, throw open on fall pressure switch. This little bell looks like a little bell, that is, a symbol for a pressure switch there's only a couple: symbols that show up all the time in air conditioning and refrigeration. Once you know them.

Actually, it's pretty simple. So this is a pressure switch, and that means that it's going to remain closed as long as the pressure is high enough and that's exactly how a low ambient control or a fan cycling switch works right. If our pressure is high enough, then the fan is going to stay on. If our pressure drops, our condensing temperature drops our condensing pressure drops, then that's going to shut off our outdoor fan motor.


It's going to break the circuit to our outdoor fan motor and it's going to shut it off right now again, if we didn't know any better, we would think well. Where is this thing you're looking all over for it, you know, okay, i know it should have that nope, not necessarily because it says right here. It's optional right, you're, not actually going to have that in most cases, very rare we're going to see that, especially in florida. Let's take a look at this switch right here.

Actually yeah, let's go up and look at the switch right here. What is this crankcase heater control? Chc? We already talked about that all right. One of the students tell me what type of switch this is somebody somebody unmute yourself and tell me what type of switch this is based on. What we've already talked about.

I'm gon na put you on the spot. Now it's thermal yeah. You can see that so it's temperature switch, but let's go through the whole name, how many poles and how many throws anyone, pole, single pole, single, throw right. It's only got one pole on it and it only, and it only connects in one direction if there's another little dot up here and if it opened it would connect to that dot.

Then we would have a single pole double throw. But it's a single pole, single throw most safeties are right in this particular case. If it gets too hot, it opens, which means that and again it's shown as normally closed. So it showed nice closed.

So that would be a single pole single, throw normally closed, open on rise, thermal switch. All that is just built right into this little picture and it makes perfect sense right. Temperature rises. It's going to shut off.

What's it going to shut off this little guy right here? What's this little guy crank case heater crankcase heater right, so if your crankcase heater control says hey compressor's hot enough, it's going to open up i'm going to shut off your crankcase heater makes perfect sense right. A lot of this stuff is really logical. All right, let's take a look at a contact. Contacts are easy.

They just look like this difference between contact and a switch and again this isn't necessarily universal. But, generally speaking, a contact is usually activated in a relay contactor starter by an electromagnetic coil, meaning it's activated by another sort of pilot duty coil and, as we know, on a contactor, we've got that electromagnetic coil on the bottom. This is a air conditioner. So that's a 24 volt coil residential single phase, air conditioner when that 20, when that 24 volt coil is energized, the circuit is made on the on the y circuit goes back to common.


On the other side, then it's going to close this switch a closed switch. A normally closed switch looks like this. Your switch on your start relay your potential relay is a normally closed. Switch means if it's just sitting there, all by itself, ain't nothing happening.

It's closed, compressor contactor, if it's just sitting there all by itself, power's all off that switch is going to be open, normally open, normally closed right. Pretty simple you're also going to see little circles like this. Whenever you see a little circle like this, that's generally going to be a relay coil. Sometimes they can also draw them as a squiggly line, but especially on modern diagrams you're, going to see them generally just being a circle.

So this is your start relay coil, and this is your start relay switch right. So when this start relay coil has a high enough back emf a high enough potential across it. Then it opens up the start, relay switch and it takes out the start capacitor out of the circuit. That's how the start capacitor works.

It starts out with the start capacitor in the circuit once that motor starts producing enough back emf, because your motor is a generator as well as a motor. It will end up creating enough potential enough voltage that it opens up or it energizes this relay coil and it opens up the um. The relay switch, that's normally closed and it takes out the start capacitor. So it doesn't burn out the compressor.

But again, in terms of symbols, knowing these symbols is really really helpful and again just a few basic ones. Coil, normally closed, switch or normally closed contact, normally open contact. What about this one right here? What is this symbol? Where you have a straight line and then you have a curvy line, what does that mean? Anybody know give me a second to drink. My cold coffee, capacitor, capacitor, yeah yeah, so you can see sc start capacitor, one straight line, one curved line.

That means the capacitor and you'll see same thing here right. This is our rc, our run capacitor straight line curved line. This is our compressor side of the dual cap. This is our fan side of the dual cap right all right, so we've talked about pressure activated switches.

It's normally closed, open on fall, normally closed, open on rise right. Some of you may not get that, but imagine if you push on this, it's already closed. So, in order for this something to change on, this switch pressure has to drop, and that would open it. In this case the pressure has to increase, and then that would open it.

So the part that stays put is always on the left side and the switch opens and closes on the right side. If that makes sense, all right, zoom out here a little bit we're going to look here at this little circuit. This is something that one of the commoners was talking about earlier. Easy heat and cooling was mentioned in this - that there are a lot of series, switch circuits or switches in series um, the first safety, so we have an lpc.


We have an hgs, we have an hpc right, low pressure, control, hot gas, switch high pressure control and then we have this time delay circuit. So this is a new one that you haven't seen before, but this little arrow guy is a time delay circuit. We have our compressor, contactor coil same thing, and this is our y circuit. So if any of these, normally close switches were to open again this one right here, high pressure, control, single pole, single, throw are normally closed.

Single pole, single, throw open on rise pressure, switch that little bell tells me it's a pressure switch. I can tell it's open on rise because it's closed and if i push on it, then this side here would rise, so that would open the circuit. This is a um uh single pole, single, throw thermal um open on fall, uh thermal switch single pole, single, throw open on fall, pressure, switch normally closed. All of them are all normally closed.

All right any questions so you're going to notice that, in terms of symbols, we got a lot more symbols on this side, so we got some information that we get over here that we don't get over here right. We don't have all this cool information about the switches and what causes them to open and close on this side. But on this side we don't have colors of wires. We don't know exactly where they're connected so you're going to have to kind of jump back and forth.

I prefer to start over here on the ladder side just to get a sense of the circuits and then once i'm tracing an individual circuit, so i've already kind of got a sense of where i want to go. Then i move over here to my point. To point or connection diagram, or in this case they're just calling it a wiring diagram cool stuff. I think i pretty much beat that dead horse.

I don't know if there's anything else, i want to cover there any any any questions anybody wants to cover before we move on to the next one, all right, so this is a well actually before i tell you, let's see if somebody can tell me what type Of equipment - this is first uh. First person to tell me, gets a gets to pet one of nathan's goats. What type of equipment is this i'm just gon na? Let you hang until somebody answers either on uh, either on youtube or the apprentices air handler uh. Close close, not quite though not quite you'll, find some things that give it away now.

I understand what you said air handler, because we got a blower there, but there's some things here that give it away, especially if you look over here at the legend i know it's probably kind of hard to see a furnace absolutely took a while, but you got There so a few things that tell us it's a furnace one of the first one, the first that i that i noticed is that it has hsi hsi. Let's see what that see, what that stands for hot surface igniter so obviously to have a hot surface. Igniter gon na have a furnace. It also talks about um gas valves and all that kind of stuff.


So what i like about gas furnaces is they have some mac, daddy, uh safety circuits in them or there's just a whole bunch of switches wired in series back to that whole switches wired in series, but let's follow before we get into it. Let's just follow the same process that we followed last time, so let's identify some of the things that are not always going to be there. So what are some things that are going to be optional here? Let's see if you can see if you can find any of them, what are some of the? What are some of the options on this? It's not as many not nearly as many optional items here, but there are some right see up here. We got, we got dashes so, and you see it says when used here when used on ls2.

So what is ls2 ls1 and 2 limit switch auto reset. So that means that there may not be an ls2. There may only be an ls1, may only be one limit switch and that's most likely - and this is something that you're also going to see a lot where's a lot of these diagrams. It's not just for factory options, it's also for a wide range of sizes.

So you may have one diagram that is for the entire uh. You know category of furnaces, so this would be uh, let's see if i can figure out hold on this is the 58 php carrier furnace, but it doesn't say what size, and so you may have one of the smaller ones. That only has one and maybe one of the larger furnace models that has more than one. So you pay attention to that also be helpful to go ahead and read.

Note number 10: if you're up here and you're confused about this, let's go to note 10 and see what it says: factory connected when bvss chimney, adapter accessory kit is not installed. So when you don't have this accessory kit, then that's going to be factory connected over here. We've got a. I saw another note up in this area - oh here, so these say when used lgps.

So what is our lgps low gas pressure switch all right? What's that all about, let's get a note, a number 11 factory connected when lgps is not used so uh and in my understanding, is that the lgps is generally going to be used on this. When you do a an adapter or sorry an adapter, a conversion to lp, because in lp you can have this drop in gas pressure as your tank goes. Uh empty and you'd wan na you'd wan na know that so sometimes you're gon na have that sometimes you're. Not going to have that and again what are you looking for you're looking for these dashy lines, right, you're? Looking for these notes, things to things to pay attention to once again, we've got information over here that we don't have over there, so red spare one orange spare two etc.

Look over here same thing: blower, it's a blower motor. They both have the same note, but here it doesn't tell you the colors right, it's giving you the circuits, but it's not giving you the colors over here on this diagram. It actually is giving you some of the safety switch information that we didn't have on that. Previous one right over on that previous one, when it had these switches, it just showed like a little.


Oh actually i'll show you what i'm talking about here. So these are switches, but they don't show them as switches. They just show them as little bars on this carrier one they do show them as switches. So you have that information about what type of switch they are, but here's this interesting thing on this uh on this point-to-point.

We can kind of trace this out, and this is actually a really common thing. You do want to pay attention to what can cause this furnace not to run well. This is a lot of things, but you see this whole battery of safeties that are all connected. One in and out of the other right and you've got a red wire going in and you got a red wire coming out, so we would start here and we could actually trace and see all right do.

I have voltage here here here here oop. I don't have it here or right or i ha or i don't have it here. I should say: okay. Well, it was all good.

Then ls1 i stopped having voltage. That's my limit switch. Okay! That's where i need to focus - and you can see these are all normally closed switches you're, also going to notice that all of these are normally closed, switches and they're. All the same type of normally closed, switch, they're, all identical.

Who wants to tell me what type of normally closed switch? These are come on. I'm waiting single pole single, throw open on rise, thermal, exactly nailed it. I can always count on jessica, yep and - and why is that? Well, it's because it's a furnace right, and so you want things to shut off when things get too hot right. So pretty obvious, you got a lot of different types that perform different functions, but they're all doing basically the same thing if it's getting too hot.

It's shutting the furnace off pretty straightforward. Now we have here kind of interesting right. This is a and it is. It is actually kind of funny here, because this is connected in the opposite direction.

I mean this. This isn't the standard that you'd see it's actually connected on this side, but you can see this is a normally open switch. I actually find a lot of things in diagrams and schematics that are kind of funny um, but you can see these are normally open switches and these are pressure switches. We already talked about what a transformer looks like this.

Is you know your traditional transformer? We have our primary connecting in here white and black, going to our white is going over here to this plug. It looks like it's kind of hard to see and that's the kind of the issue with a lot of these diagrams is it's kind of hard to tell yep it's going over to this plug and that is energizing our transformer and then black. It's going here to our pr1, our primary one, but if we look over here, let's try to find the same thing see if we can find on our schematic the same um same transformer and actually i'm having a hard time. Locating it here.


So, let's see we got l1 and l2 right, let's see if we can find our transformer. Oh here, it is right here, so we've got 115 volts here and now this all is our low voltage side. This is all of our high voltage side. This is all our low voltage side and that's going to be very typical now again with an old school ladder schematic.

This would all be in the center. You'd have two lines running down either side, and it would be much more clean nowadays, even with your ladder. Schematics they're not as much ladder as they used to be. I mean it's still a schematic, but you don't have as much of l1 on one side.

L2. On the other side, you know you're, on your secondary 24 volts on either side, they're kind of more of a composite of a connection diagram and a and a schematic diagram which, for an old-timer like me, drives me nuts. You know it was fine. The way it used to be, i don't know what i always got changed.

Everything kids today, engineers lame engineers for everything all right um. So that's that's the safety circuit. Now, let's go through and actually see if we can identify some things, so we're gon na we're gon na scroll to our next hold on all right. So let's pick out some stuff on this furnace and see if we can actually identify it now i didn't you know i i could have given more complete pictures here which may have made it a little bit easier.

But let's, let's try to find something. So first thing: let's try to find a fuse. We got our fuse here and we've got sec2 and sec1 connecting right under it. So, let's see if we can find that on our diagram, let's start over here, sec 2 sec 1 and then we have our views.

So you can see for me at least that was a little easier to find over here, because the transformer is right here now, if i go over here and i'm trying to find it all right, there's sec 1 scc2 but where's the fuse. Oh there. It is, but it's not even shown in the circuit right, fu1 fuse. That's not very nice for it to say fu like that very rude, a three amp automotive, automotive blade type factory installed fuse all right.

We got a note here. Let's see what that note is. I think it's, i think, that's note. Number six looks like replace only with a three amp fuse.

Okay. Well, i mean that's so there's some additional information over there, but for me at least it was easier to start at the transformer scc1 scc2 and find my fuse right here. All right. Let's see, let's see what else we can find we're not going to do all of this, but i'm just giving examples of things that that you would do um.


I wish i had a better picture of this, but let's see if we can find this, this ribbon plug now. So when you're trying to identify something like a like a plug or a connector, it's usually going to be easier to find on the connection diagram or your point-to-point diagram. And the reason is: is that all these wires on your schematic, your ladder schematic, could be all over the place, because your ladder schematic doesn't care where it? You know whether things are close to each other in real life, but on your point-to-point it should be easier. So, let's see if we can find it, where is that ribbon, cable or that that connector, it's not really a ribbon cable but that connector on this diagram over here, let's go back again: you're gon na notice we've got a blue on top and then a red And red and all that looks like you got a white here down at the bottom.

I think right here, right, that's and you can kind of identify it because they sort of put it in proximity on the pcb anybody know. What pcb is anybody credit circuit board printed circuit board? There you go, you did it and it says it right here too. What well anyway, i was gon na, say phantom off city beach, panama city beach, yes, also very, very, very good, very good, which is a lot of people believe is in florida, but actually it is in southern alabama. We do not claim the panhandle is actually florida because they be cray-cray up in there.

Hopefully, hopefully, there's no panhandle people listening all right print in circuit board, that's right and so everything here - and this is actually another interesting thing that you're going to see on a lot of connection diagrams, and so this kind of bounds, the printed circuit board, and so Things are going to be laid out here on this board. The way they kind of are in real life, so we've got this connector and these are going to be numbered. I don't have a great picture here of the numbers, but these are going to be numbered. In fact, it says right here: pl1, let's see if it says pl1 sure enough there it is pl1 plug one all right now, let's see if we can find this right here, our motor speed taps see if we can find those.

Oh there they are pretty easy. 24 volt motor taps right there, because everything is kind of drawn in proximity. So it's much easier to identify what's on here, on which one of these diagrams, which one of these diagrams, is easier to find things in real life, where they're located connection diagram right schematic. Finding these same things now we can do something like all right.

So we know this is pl1, so we can try to find pl1 over here, but i don't know that we're i mean so yeah. Here's pl1, but i mean it's not everything's kind of all over the place right, pl, 1-1, pl. 1-9. Po-1-11.

Each connection is completely separate on a ladder on a ladder schematic. Let's do a little more here. What about our field connections? What are we looking for? In order to find field connections on one of these diagrams, based on what we've talked about, i'm waiting one of you. What are we looking for field connections? What dash line? That's right, we're looking for a dashed line.


So, let's see if we can find some dashed lines that are going to work for this, i kind of i kind of misspoke there, because here they're not actually showing your field wires coming into these fire nuts wire nuts yeah. You could be looking for wire nuts, but here it's not actually even showing them it's not showing your wires coming in now. As far as our high voltage coming in these right here or this, you know it comes into this box. We can probably find that with a dashed line, let's see white black ground.

Those are our dashed lines right coming into our jb. What is our jb junction box? What does it say here on note number two, because it applies to our high voltage, let's see what it says, use only copper wire between the disconnect switch and the furnace junction box; okay, so no aluminum, no aluminum for you. We've got a fuse fu number two.

11 thoughts on “Electrical schematics & circuit tracing”
  1. Avataaar/Circle Created with python_avatars AkimboJonesx21 says:

    As someone who has worked on boilers, the electrical outside the unit has no electrical diagram. You have to trace everything out. The best way to learn how to read an electrical diagram is to trace the wires out and then to compare it to the diagram. Know the road then find the road stops.

  2. Avataaar/Circle Created with python_avatars Brian Mcdermott says:

    Great info. Bryan. Thank you.

  3. Avataaar/Circle Created with python_avatars Nathan Hurst says:

    Thanks for all you do for our trade, I’ve been at this for 12 years and even though I’ve got this down really good I still really enjoy these videos. If people will listen close enough quite there’s often little nuggets of info that even us who’ve been at it awhile “remember some things we’ve forgotten”. That sounds really familiar for some reason 🤣 Are you in Nepean ?

  4. Avataaar/Circle Created with python_avatars Eassyheat/ Cooling says:

    🍺👍

  5. Avataaar/Circle Created with python_avatars Michael Costello says:

    You did not mention the optional box in the top middle of wiring diagram (CE OPT). its a bit confusing. Thanks for video

  6. Avataaar/Circle Created with python_avatars Luke D says:

    Thanks Bryan as always, I really appreciate your efforts 🙏❤

  7. Avataaar/Circle Created with python_avatars Duane Quan says:

    Thanks for this. This would be awesome if you could upload your classes to Youtube. These videos are very helpful. Been watching your videos since I started school for HVAC

  8. Avataaar/Circle Created with python_avatars Bleebleblahble88 says:

    Thank you!

  9. Avataaar/Circle Created with python_avatars Russell Bailey says:

    Russell from Columbia ,TN Service area Barrhaven??

  10. Avataaar/Circle Created with python_avatars Christopher Borner says:

    Chris from Milwaukee, WI

  11. Avataaar/Circle Created with python_avatars Luis Medina says:

    Thank you very much!

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