This episode of the HVC school podcast is made possible because of the generous support in so many ways from testo rector seal and carrier, and I want to mention I'm going to be at ahr the HR conference in Chicago this January, starting on January 22nd, which is A Monday January 22nd, 2018 I'm gon na, be at the HR conference, and for those of you who listen to the podcast and would like to hang out, I'm gon na try to grab lunch from dinner with some of you, maybe breakfast who knows my brother, Nathan's Gon na be there, some of you know him from the Facebook group and then we're gon na have a great time. I hope to see many of you there, but one way to to see me and also see a pretty cool tool is by going to actually seeing me and seeing a cool tool might be the same thing anyway. I digress is by going to the erector seal booth, and so that is booths 25:45 at ahr and from 2 p.m. to 4 p.m.

on the january 23rd, which is Tuesday, I'm gon na be demonstrating the pro fit tool, so I'll probably demonstrate a couple times. If you have questions for me or anything you want to talk about, you can come by and talk to me there. It's director steel booth, but you can also enter to win at the rector steel booth for a proof, if I'm not mistaken - and don't quote me on this - but I think they're giving away one of the prophit flair kits and then also a swedge kit. The new swedge kit that they make and it's a really Pro for those you don't know a pro fit is Pro fit, is a really great flaring and swedging tool that you can use.

It just goes onto a drill or an impact. It has a Chuck on it. It's made primarily for high rpm drills, so you got ta, have a good quality drill, but you can make a really really nice flare and swedge with that tool. The flare, the the flare gets already out.

Swedge kit will be out very soon. I would also encourage you to go check out the test. Oh booth, 73-65, I'm going to be in and out of that booth as well. They've got a lot of great products.

A lot of new products that they're gon na be rolling out here very soon again, I've told you many times that I like a lot of the tester products. Two of the products that I use all the time are the test of 770 3 multimeters, the multimeter that I use so for all the tests in this podcast for voltage and resistance. That is the that's my go-to multimeter, that's in my go-bag, of course, I don't go as much as I used to, but a lot of my technicians have also used the 770 3 and liked it a lot and then also the test. Oh 550.

Manifold is sort of our go-to workhorse manifold that we used throughout my company. It's just a great reliable manifold when it comes to the digital manifold is very, very accurate. It uses thermistor probes instead of thermocouple probes, which means that they're more accurate on the temperature reading. It just does a great job and we, as it connects to the app which a lot of my technicians use, especially for like measuring pressure drop when they're doing a standard nitrogen test.

It's really good for that. Just a lot a lot of really really great products over I test. Oh so you can go see them at 73-65 and you might see me there as well look forward to look forward to meeting you at ahr that is Chicago McCormick place starting on January 22nd. That's a Monday and I'm gon na be specifically at the rector steel booth on January 23rd, which is Tuesday from 2 p.m.

to 4 p.m. hope to see you. There beat zoom on the 10 second flame, free refrigerant, fitting from Parker reduced labor costs by sixty percent. With no brazing no flame had no fire spotter discover how Siouxland can help you be more efficient and productive visit, zoom lot com for more information, and now the man who tries to explain makeup air and ventilation to his kids whenever they eat out brian or hello, Hello, this is brian with the hvac school podcast.

This is the podcast that reminds you of things that you might have forgotten along the way about the hvac, our heating, ventilating and air conditioning and refrigeration service arena. Or it reminds you of some things that you may not have known in the first place and today on the podcast, we're talking about voltage and resistance when I'm talking about amperage today, amperage is gon na get left out today, amperage and wattage they're sitting on the Sidelines we don't need them in the game, but we may call on them shortly so because this is just me talking, I'm not gon na. Do the typical you know, like intro thing, where I intro the host that'd be kind of weird. If I enjoyed myself like read you my my credentials, first of all actually actually be kind of short, so we'll just skip that, but but today we're gon na talk about actually using a multimeter and some things that you may notice, because you know it's interesting.

If you, if you go on any of the Facebook groups, and somebody asks a question about motor load and how it's affected by voltage or just different questions like that people will just start saying: Ohm's law, it's Ohm's law, you should know Ohm's law, you don't know Homes law go back to school, but it's interesting because in the real world very few of us ever work, Ohm's law - I mean how often have you actually sat down and used Ohm's law in a practical way, and so, let's, let's use a practical example here. Let's say you take a compressor and you ohm it out, and so you take. Let's say: let's say that compressor says that it has. You know three ohms on one of the windings okay and if you take Ohm's law, you take 3.

What I'm pulling out my handy-dandy calculator here? This is pretty complicated, math here, so actually gon na take because it's e equals I times R, so volts equals amps times resistance. So if the resistance is 3 ohms we're gon na take the the volts of the compressor. So that's 240 we're going to fight that by 3 and that's gon na give us our amperage right. Whoa, 80 amps! That's really high that compressors going to draw really high amps! The fact is is that the compressor does actually draw at high amps initially when it starts up, that's what we call locked rotor ramp, so we actually this long conversation on the Facebook group recently I did a video on it.

If you want to about that, you can go to Facebook, look up, HVAC school in the groups section and let go over there, and you can see that video that I did and some of the heated debate that followed and it mostly followed. Because I said you don't always need to oh man a compressor, but I digress we're not going to talk about that as much today. We've touched on it slightly, but if you take that math - and you say - okay well - that compressor is going to draw amps will actually know that compressors not gon na draw 80 amps, because the real resistance in a motor I mean there is, there is resistance that You can measure with the motor de-energized and that's what we just did we measured the ohms on the on the windings de-energize, but as soon as you energize, those windings there's additional resistance, that's added because of the expanding and contracting a magnetic field. So this is one of my favorite topics to talk about.

It's just a it's a nerdy thing, but it is practical, and so, if you listen to past podcast you'll hear me talk about inductive reactance and that's what that is. Inductive reactance is electromagnetic resistance. That only occurs when the motor is running and if you've ever tried to ohm out a motor or a solenoid or any type of electromagnet, any type of inductive load of magnetic load. You will have observed this that the resistance seems low, or I mean when you do the math.

When you work Oma's law, the resistance seems low, but the only way to really get that resistance truly on an electromagnet is to energize it with the design voltage and then measure the amp will amperage. And then you can back into what the total resistance is or what the total impedance is. And so, when we say, impedance impedance is measured in ohms and impedance is equal to both the traditional resistance. The resistance that you can measure with no power applied plus the inductive reactance, so the resistance of the winding plus the inductive reactance, the magnetic resistance, and so let's say that we were to power this.

This compressor up. We would have to take both windings and then we would. We would take the take the voltage on each winding and then we would take the amperage of each winding and then by that we could calculate the the actual impedance and you also have to take into account the capacitive reactance of the of the run capacitor. So it's not it's not a calculation that we typically are going to do we're not really trying to figure out what the impedance is of a compressor regularly we're just measuring what the resistance of those wine are with it without it being energized, which you just can't Work, Ohm's law - just isn't isn't that simple, and then you also have to you know whenever you're talking about alternating current, you also have to take into account for power factor.

So, there's just a lot of different a lot of different factors there, so Ohm's law in a practical sense. We don't use it a whole lot. At least we don't use it for the math, but we do use it for is we use it to understand the relationships between these three things, specifically in Ohm's law, we're talking about the relationships between voltage, between amperage and between resistance and when we think of something. Let's start with something really simple here, and so we are kind of we're just we're just kind of backing into this, so we're gon na get into how to actually use a meter and one what some of the stuff means and how it's practical.

But let's let's, let's talk about something really practical like the most simple load that exists would be a light bulb I'm and that's what we and so we typically think of when we draw when we draw our most basic diagrams when we create really basic projects to Show someone how to use a switch and how to wire up a load now to wear up a power source with a battery we're always using a light bulb. So we think of a light bulb as being a very, very simple type of a load. But before we even do that before we even do the light bulb, let me just take a quick breath here. It's nice and calm.

I start talking a little fast when I get a little excited talking about this kind of stuff. What is a load in the first place? I mean: what is it really so I define it generally on the podcast and a lot of other people will define it this way too. It's the part in an electrical circuit that actually does something it's the part that does work right well, is that is that really what's happening? What is really happening inside of a a load mold? It has electrical resistance and the result of that electrical resistance. It really is it the result of the electrical resistance.

It isn't even quite that simple, but we'll just say that, for the case of simplicity, we'll say the result of that electrical resistance can be electromagnetism, that's pulling in the solenoid that is creating and expanding and collapsing electromagnetic field that creates rotational force. In the case of a motor, that's a solenoid, that's a even a speaker, you know, like a speaker, is an inductive load. It actually sends magnetic impulses and that drives and creates error. Vibrations drives a diaphragm on a speaker and creates vibrations in the air that we recognize and our eardrums as having meaning as having sound to replicate something.

So we see electromagnetic loads all the time and they do something they vibrate a diaphragm. In the case of a speaker, they draw on a solenoid in the case of a reversing valve coil, for example, or a contactor solenoid that pulls in those contact points. It spins a motor. You can dress some of those, so those are common, but then we also have resistive loads and resistive loads generally create light and heat or what we call you know we say, creates it.

It doesn't create anything in reality, you're just changing energy from one one type of energy to another, so the movement of electrons is then being converted into light and heat, something that we can something that we can sense. So a load is the part that does that thing: let's not overthink it here and we can go in an engineer's direction with any of these things and look at them far more technically and far more mathematically. But that really the point of this is to say that, as far as the technician is concerned, if you work in this field, you care about the relationships between things and understanding how they, how they go together, not so much the ability to always replicate the math. There are some areas where math makes more difference, but in electrical, especially you're, not gon na do a lot of electrical math as an HVAC ER technician, just not gon na happen that often, and if you do need to do it well, then you just know where To look it up, so you can find it I mean, remember, equals I times R.

That's it's pretty pretty simple! That's Ohm's law, very basic, but anyway, so I digress. So we think about a a light bulb - and you say: okay I'll, like Bob what is fixed on a light bulb, and this is where people get the the most confused. Whenever I do these sorts of quizzes or anything like this, with light bulbs or heat strips or whatever I'll say what is fixed on a light, bulb well they'll, say well, the wattage Schrank is the one, the light bulbs, rated at 100 watts or 50 watts or 40 Watts 30 Watts whatever well. The water digit isn't actually fixed.

The wattage is fixed because it has a rated voltage and so for an average light bulb that we plug into a socket in our house, is rated for a specific voltage of 120 volts. In most cases, 110 115 120 volts, and so it's at that voltage that lightbulb will be a particular wattage and so there's an assumption rate, and the assumption is that the voltage is fixed. Now, if I change the voltage, then that will also change the wattage of the bulb. I mean it's pretty clear that it will, but when people look at Ohm's law, they look at Watts law, they get these things convoluted because they think that the wattage is fixed.

So they assume that well, if the wattage is fixed and you change the voltage well, then the amperage must go up in order to keep the wattage the same. But of course it doesn't do that a light bulb. Is it's rated for a particular wattage, but it's the assumption is made by the light bulb manufacturer that you're going to apply a fixed voltage, and so when you change that voltage, you change the wattage output of the bulb or, and you know in actuality what the Bulb is really doing is outputting lumens, so you can have a you, have a bulb, that's rated at a specific lumens which is actually the light output and you could say: well, it's the lumens, that's fixed! Well, no, it's not the lumens that are fixed. The lumens are fixed, it will output this much light if it's provided this particular voltage and then it will then produce this particular amperage which results in a specific wattage.

So this is all and we have this an output, but there's an assumption and the assumption is that you are providing the proper per debt potential difference, the proper voltage that the bulb requires, and so you say: okay well, if the, if the wattage or the lumens Aren't really fixed then what's fixed is the resistance, then the resistance is fixed, and so I should be able to take this bulb and I should be able to ohm it out, and it should give me the resistance of this bulb and I should be able to Work Ohm's law and tell exactly what the amperage will be and then I can, you know calculate that with the voltage and then I should be able to get the the wattage right and then that will tell me you know that's fixed, it's the resistance, that's fixed! Well, actually not and here's why? Because, as the filament and the ball, which the filaments, the part that gets hot, the part that lights up on a typical incandescent light bulb, which again we're talking incandescent or not talking LEDs we're not talking fluorescents. Those are different methods of producing light on an incandescent bulb. As that filament heats. It actually has a higher resistance.

So initially, when that bulb, if you were able to measure this on the very like it's very quick, you had a meter, they could just catch this right away in the first couple cycles. You would notice that when the when the filament is cold, it has a lower resistance and therefore draws higher amperage. Then, when that filament heats up - and this is true of most conductors now - this isn't a universal rule about all different types of matter or everything. But for most conductors when a conductor is hot, it has a higher resistance and when a conductor is cold, it has a lower resistance.

Now that sounds that may be either counterintuitive or intuitive for you, depending on how far along the path you are with electrical Theory or electrical understanding. But here's. What you have to recognize is that the more current that goes through a lightbulb filament, the more resistance there is and the more resistance there is, the less current can go through the lightbulb filament. So those two things are kind of those ideas are opposed to each other right, but but it's self regulate.

So it hits this point in a self regulation, whereas it once it hits a certain temperature, then the resistance is increased to a certain point. That then regulates it so that it doesn't keep getting hotter and hotter. Actually, I mean, if you think so I'll give you a second to wrap your head around that, but again, the fact is is that when resistance on something is higher - and this is what Ohm's law does tell us - when resistance is higher, amperage or current is lower. So long as the voltage stays fixed and in a typical you know commercial, residential application.

We we see the voltage generally in most running operations. It stays fairly fixed rate of 120 volts at the outlet that doesn't fluctuate a whole lot in most cases, and so the voltage is fixed, and so, if we increase the resistance, then the amperage decreases. If we decrease the resistance, then the amperage increases. That's what we call an inverse relationship, so it's not! You know the amperage doesn't go up with the resistance.

The amperage goes up when the resistance goes down. The amperes goes down when the resistance goes up, that's known as an inverse relationship, but in a light bulb. What we're saying is is that if you were to own a light bulb out, you would think that the amperage should be higher and therefore the wattage would be higher, but once you actually apply the rated voltage to it, you find out that it actually, the amperage Is actually lower, the wattage is actually or than what you would think just by oh man get out because, as that filament heats, the resistance of the filament increases. Okay, now you're probably wondering why why the heck is this important? Well, it's important because when we throw around a phrase like Ohm's law, we throw in a phrase like Watts law, you have to understand.

What's what is the constant in this equation or how do you figure out the variability or the dynamic range in an equation? How do you figure out the change in an equation then, and for most of us in the field? We're not engineers, and so we can understand a concept like Ohm's law and we can understand it in a broad stamp from a broad standpoint and we can get a good sense of it. And that's good for us to do it's good for us to understand those relationships like, for example, that, when electrical resistance decreases current increases. That's that's good for us to recognize that right or when voltage increases. If the resistance remains the same, then the amperage increases, but to do the actual math is trickier than we think it is because even things that we think should be fixed like, for example, the resistance of something really never is fixed, and it really never is fixed Temperature changes affect the resistance of a substance and, when you're dealing with an electromagnetic load, an inductive load, the resistance changes, whether or not the load is energized or de-energized, and it also changes with you know when you have a like something like an electric motor.

For example, the frequency that that motor is allowed to spin meaning. How fast is that rotor the part that actually turns in a motor allowed to spend in relationship to the stator, the part that stays stationary? How is it allowed to get close to the frequent synchronous speed or is it forced to lag because it's put under more load that affects the resistance in those electrical windings which results in changes in resistance or changes in impedance of that circuit and again just to Be clear when I say impedance impedance is just the inductive reactance in addition to that resistance that you can measure initially with a with an ohm meter. So why am I telling you all of this? It's an important to set the stage for using a multimeter, because the first key to using any tool is knowing its limitations. If you don't know the limitations of your tool, then you're going to be given false confidence and there's nothing worse for a diagnostician than false confidence.

I mean. Maybe the other thing would just be complete incompetence, where somebody knows that they and they still just you, know, walk away from it or ever I mean you see, technicians do that from time to time, but but you have once you get past that first stage of Knowing that you don't know, the next stage is thinking that you know where technicians think they understand and they think that their tools are providing them with this answer that, in fact, their tools aren't providing them with. So let's take a common one. We're just gon na use some very common scenarios here, I'm not going to get super.

I'm not gon na get super technical like it, for example, describing how to read a diagram on a podcast is essentially pointless, but there are some things that relate to how we talk about diagnosis, so the kind of thing that you'll call a buddy or a senior Tech and ask them about that that we can talk about in a podcast. So let's, let's use a common one, let's say: you're working on a heat pump, condenser and a heat pump condenser. So, just for the sake of clarity, it's just a basic single stage: residential heat pump. Condenser.

You have a couple wires. You have more wires than what you would normally have with a straight cooler. You would normally only see, yellow and blue. It's really just in a straight cool and a lot of cases: you're just energizing the contactor and a simple straight goal, but on a simple heat pump, you've got red, you've got, yellow you've got blue, you've got white, you've got orange okay, so you've got multiple multiple Conductors there and they all do different things, they serve different purposes, and then you also have common.

I don't know if I said blue already, but you also have common. So a lot of technicians LED a newer technician, still they'll call until they'll call me and they'll say: hey I've got I've, my contactors not pulling in all right. Well, what do you? What are you reading at your contactor? Well, I've got 24 volts, they'll say just like that. I've got 24 volts all right and I've learned over time not to trust that, because they'll they'll just want to be like I've got 24 volts and it's not pulling in what do you think it is all right? Where are you reading 24 volts with the two leads of your meter, so senior Tech's out there? That's the next question any time someone says: they've got voltage, I'm doing air quotes here, they've got it.

You've got to define what two points aren't they reading between, because on a voltmeter, you're always reading between two points and what I tell and I've talked about this on a recent podcast. But whenever you're using a voltmeter you're only going to read voltage if you're reading against across two points that have a difference in charges and for them to have a difference in charges, there needs to be a reason for them to have a difference in charges. Just because they both have potential meaning they both have voltage in reference to ground or neutral does not mean that there's going to be a difference in charges between the two points that you've chosen, so a common one will be a technician will say, like I just Said I don't have I don't have Ulta Jim my contact? Okay. Well, were you reading between? Well, I've got nothing in between yellow and red okay yeah.

Most of you know if you've done this for a while. You know that. That's not how you do that you either read across the contactor coil itself, which is kind of my preferred place to start or you could read, between, yellow and blue coming in. That would tell you something blue being common on the opposite side of the circuit from red.

So when you read between yellow and red, what are you really doing? Okay, so think of this, as in the terms of us very simple, very simple diagram, so you've got you've, got 24 volt potential. That's between the two secondary legs on the transformer, so you know primary is the high voltage coming into the transformer if two wires coming in there that energize the primary and then you have the secondary, that's energized and there's differential there's differences in potential between those two Points on the secondary, so those those colors might be red and green. That's a real common one for the secondary on a transformer and the colors, don't matter, but there's a difference in charges between those red and green wires there, and so you make a circuit in between those two wires and it needs to go in most cases. You're gon na have the hot line which, what we call hot, we'll use red and we're looking at a diagram.

That's on the left side of a diagram, and then you go to a thermostat and the thermostat is both a low din to switch. But it's primarily a switch, and so it switches in between that red and the different legs of power and the different on the. What we would call the load side of the switch is what comes out of the thermostat, so so that yellow wire is what we would call a load side or a switched leg, and so that yellow wire is now energized. If that thermostat is closed, and so there's no potential difference between red and yellow, if a couple different scenarios happen, you would have no potential between red and yellow if both red and yellow are energized with 24 volts potential 2.

In reference to the common side of the circuit, you would have nothing. You would read nothing between those two points. You would read nothing between those two points. If there was no power on the circuit whatsoever right, you would also read nothing between those two points.

You could also read nothing between those two points. If say, the contactor coil was completely open, or if there was there was a the you know. The common was open so that there was no circuit all the way through because and then at that point, even though you are reading across an open switch, there would still be no difference in potential, because so imagine it this way. Imagine that you have a contactor coil, that's fully open, it's cut inside that contactor, coil and so in between the Wye terminal on the thermostat and that contactor coil, there's no connection to anything else now again we're using a theoretical system here, sometimes you can get bleed Through on certain types of controls, or whatever, I wasn't talking about a very simple theoretical system here and so between, why that why terminal on the thermostat and that cut contactor coil, if that thermostat is off so cooling is set to off now, there's no potential in Between why and that cut coil portion right, and so, if I read in between red and that why I'm not gon na read anything because there's no path to anything, it's it's an a little isolated segment of wire.

Essentially, it's doing nothing, and so it's so reading between red and yellow at the condenser tells me basically nothing because if the switch is closed already nothing if the switch is open, but the circuit isn't intact already nothing and if nothing is energized. There's no power on red or yellow, then I'll also read nothing, and so it doesn't give me much good information in comparison to checking between yellow and common, because between yellow and common, that's telling me do. I have 24 volts coming out of that switch, which is the thermostat between the Hat point in the other side of the load. 24 volts difference in charges between those two points.

Okay, so that's it! That's a you know, common thing that people will get mistaken is trying to read in between two hot legs or a line in the load side leg across the switch. While that can be valuable in some cases, it's not as valuable because you have to know some other pieces of information in order to know whether or not you have any potential on that circuit at all. At that point, all right, so that was kind of a complicated thing to way to go around and tell you that when you're using a voltmeter, you generally want to plant on the low voltage voltage diagnosis you want to plant one of your leads on the common Side and then kind of walk your way through the circuit, with the hot lead and not try to read in between a line and a line and a load side of a switch and not use ground as a reference point, because you don't know how reliable that Reference point: is you don't know how well ground is connected back to a transformer or to anything else. Ground isn't isn't what you want to use for diagnosis in almost every circumstance so, and I've beat that dead horse in the past, so we're moving on from there.

But I just wanted to give an example of how technicians can trust a meter to tell themselves. Oh I've got 24 volts or no, I don't have 24 volts and what they really need to be thinking about is. Where do I have? These two meter leads placed, and it are they placed in a position that there should be a difference in potential. So now, let's answer the question: when do we see a difference in potential between meter leads and where we start here isn't isn't maybe as simple as a lot of you, because you know whenever we talk about see, sort of more basic things, a lot of senior Technicians come out of the woodwork and say well, that's obvious.

Just use common sense had somebody to say this facility just just use common sense and a meter, and I'm thinking to myself using a meter is not common sense. You know using a meter is something that you have to be trained, how to do, but here's the first question that I want you to answer. Alright, when you're looking at diagnosing something specifically with a volt meter. Are you working with dynamic current or are you not dealing with dynamic current? Are you dealing with just simply potential, because when you have dynamic current meaning, you actually have current moving, you treat the circuit a little differently than you do when you do not.

Let's give an example, so let's say you walk up to a light bulb we'll just use the lightbulb example here and you walk up to a light bulb and the light bulb is not lit. You put an amp clamp on the light bulb and there's zero amps. All right at that point, you know that on that particular circuit, it is not dying. It there's no dynamic current the light bulbs not lit no work is happening and there's no amperage on the circuit.

All right - and this is the there's tons of different examples of this - this is when you go up to a contactor and it is not pulled in or do you walk up to a condenser fan motor and it is not running. These are cases where you have a circuit and that circuit is not doing anything and not just not doing what it's intended to do, but doesn't appear to be doing anything. And so then you clamp an amp clamp on it and I said: wasn't gon na talk about amperage but shoot I did anyway, but you can even have claim on it. It's not doing anything.

So at that point you don't have a you either don't have any potential difference in the circuit. It also be like my wreckers off my fuses blow and something like that. There's you know either there's no there's no voltage applied and I don't at all know no potential difference or there's something in the circuit. That's that's broken.

The circuit is open right. So that can be a lot of different reasons. You know in a motor that could be a thermal overload, it could be a switch, that's open, it could be a safety, that's open, it could be a lot of things, but all we know is at this point that there is no dynamic. Electrons dynamic just means moving, the electrons aren't moving, there's no current.

We don't have current on this circuit. Okay, so that's the first thing you really need to assess when you're looking at a circuit is, is work being done here actively because it does affect how you how you make decisions about testing, and so, let's give an example. Let's say you have a contactor, that's not pulling in right! Well, in most cases when you have a contact that it's not pulling in, you are already going to have Devine some information about. What's going on well before the contactor you're gon na say alright.

First off is the thermostat lit up? Okay, what's lit up, but it has batteries all right. Well, so maybe that's not so valuable, but but the blower is running all right. Well, the blower is running then. At that point we know that we have 24 volt power.

We've got: we've got some 24 volt potential at the outlet or the secondary of the transformer, and we also know that the thermostats doing something blow the blowers on. So it's feeding through to the G circuit somehow or the white circle something's bringing the blower on right. So at that point we kind of have already decided that we've got 24 volts in this system somewhere, and so then you may go out to the condenser or you may go to the air handler and you may check all right. Do I have between Y and C so I'm already kind of skipping to the switch leg of the thermostat now once? Okay, obviously, I'm gon na go, make sure the thermostat set to cool and that it's ready to run, but once that's all good - and I know that okay, now my blowers running and I go outside and the contact you're still not pulling in well, then I'm gon Na go, like I said, between why and see if they at the condenser, which is checking in between the load side of the switch, so lines is read.

Load side is why coming out of the switch, which is the thermostat load side of switch Y and common, which is my reference point. It's the other side of the circuit and I'm gon na check for 24 volts there or I'm gon na check, even preferably across the contactor coil itself, and what I'm doing at that point is I'm saying all right, I'm making it as not an assumption, but I'm Making a decision that this circuit has 24 volts, the 24 volts exists because I'm seeing other things operating in this in the system, and so now, I'm gon na see do I have 24 volts applied to this contactor, and so, let's just do it's a really easy Test because if the contactor is not pulling in and I take, my 2 meter leads and I go across that contactor and I've got 24 volts. I make the decision that that contactor is not pulling in, because the contactor coil is open, because at that point, if I measure 24 volts there across it, meaning 1 1 lead on one side of the coil, which is actually the solenoid that pulls that in one Lead on the other side of that coil, I should have 24 volts there if everything's calling and if I do have 24 volts there and the contactors not pulling in well it's the fault of the contactor right and in most cases that is going to be correct. Unless something really odd is going on or here's, your meter was stuck on a lock or something and still reading 24 volts from the previous measurement that you took.

If you actually do have 24 volt supplied and consistent at that point, that contactor should be pulling in. If it's a 24 volt rated contactor and if it's not, then you can, you can say the contactor is bad. Now what you would do next? What I would do next is just to just to prove myself once I pull that contactor out, I'm gon na put it on the ohm scale, which is resistance, and I'm gon na read across the coil of that contact or what I'm expecting to see, because I've Made the decision that the contactors failed, it had 24 volt supply to it that that coil on that contactor solenoid is going to be open, not shorted, because if it was shorted, it would be blowing the fuse. The fact that it had 24 volt supply - and it's doing nothing would mean that it would be open, and when I am across it, I expect to see o L or infinite ohms.

I expect to see no path. If all of a sudden, I do see a path when I'm gon na second-guess myself, okay, that's the reason why I'm doing that tests just to reconfirm what it is. I already read - and you may say: well you've done enough already you've already read the applied voltage. I the you're right you're right about that.

That is enough of a test, but I'm all I'm gon na do that anyway, I'm just gon na ohm across the coil. Now, here's what I'm not doing, I'm not looking for a specific ohm reading across that coil, because I don't know what ohm reading that coil should be unless I have another one of those exact same contactors that I can compare to. I don't know what the correct ohm rating is, so here's what a lot of technicians do in this case and again this gets back to the point of this, is you know some basic education on how to use a meter, reading resistance and voltage voltmeter and o Meter, but what I'm not gon na do is I'm not gon na read across that thing and say: oh, it's! Reading 11 ohms! That sounds wrong to me. I'm not gon na.

Do that, because, at this point, what I've just done is I've said that if what I said was wrong with it, which is an open circuit, I was reading 24 volts applied across it and it wasn't pulling in the only thing that can cause. That is an open circuit, unless I mean, of course, of course now don't get me wrong. If you have 24 volts applied to it and think sitting there gone mm-hmm, you know it's trying to pull in and it's not pulling and I'm saying the things doing nothing right. It's not functioning as electromagnet, it is an open circuit and then I read ohms across in and I'm reading, ohms, I'm not gon na say hmm does that seem right, and this is what a lot of technicians do.

Another thing they'll do is they'll they'll see a circuit, that's blowing a fuse. I mean this is you know, blown fuses are one of the most commonly misdiagnosed problems and they will they'll go and they'll omma out the the contact to grow. They'll just run to the contact on the omote out and they'll say: oh well, it's oming out at whatever the whatever ohms you you come up with actually hold on here. I've got my got a couple contactors right here and I've got a meter there.

It is alright, so this let's go Matt so Matt. These contactors you've got a single pole and a two pole that I use for for demonstration purposes. So, let's see we get the the coil on the two pole is 10 point 6 ohms and the coil on the single pole is sixteen point. Four ohms and I could say: well, they don't match up.

You know this. This one with the high ohms is a problem or the one with the low homes is a problem or whatever or a lot of technicians say. Oh it's ringing out right here that it's ringing out that ringing out. That means that it's uh.

That means this bat means the coil shorted right. Well, the ringing is just as just a setting on the meter and that's just that's just a continuity setting saying that there is a path right and then the setting of that varies from meter 2 meter. You know when it rings and when it doesn't ring, and so a lot of technicians will try to divine something by that information by the that Ohm's information that I just gave you that resistance reading and really all I'm looking for when I'm homing it out is Just to see I thought it was going to be open based on what I measured and so is it open and if it's open then all is good. If it's not open, then I'm gon na double check myself check yourself for you wreck yourself.

As they say. It's always good to double check yourself, but that's the that's. The fear that I have in a lot of different tests that technicians do is why are you doing it? What is the result that you hope to see in the case of me oming out the coil? I'm owning it out because I want to see if it's open, like I had come to the conclusion that it was so I'm just proving my conclusion: is it always worthless to O mouth contact? Your calls? No, it's not always worthless. If you have two of the same contactor coils or you know what the resistance should be with it in its static state, then that's totally fine but oming.

That out. Let's say if I ohm that out and then I tried to work Ohm's law to tell me what the amperage would be on that coil. I would be totally wrong. I mean let's just let's just do the math here Sofie.

If we take her already forgot what I said well, one of them was sixteen point. Four, that's right! It's a single pole, 16 point for dandy calculator here. So sixteen point four well actually no, we got to do this, so we got to take 24 divided by sixteen point. Four equals one point.

Four, six amps, I think better, not draw one point. Four, six amps that'd be very high. Contactor jjal, you know the five amp using the thing, just as the just as the overcurrent protector. So obviously, it's not going to draw 1.46 once that solenoid is energized in those flux, lines start to expand and collapse, and there you're going to have inductive reactance, which is going to add to the resistance which is going to decrease the amps.

And I don't know what it's going to be. I just know that it's not going to be that high, and so I understand the resistor the relationships between these things and I also understand what my limitations are - that I'm not gon na use this ohm meter to try to take ohms and tell me whether or Not a typical residential contactor if whether the ohms are right, I'm not looking to see if the ohms are right, I'm looking to see if the thing is open or closed now, if the thing was drawn, it had, you know, point zero 1, ohms, 0.1, ohms yeah. Okay at that point, I would know that - that's that's a that's akin to a short. So in most cases when I'm using an ohm meter, I'm not really looking to read the ohm value.

I'm looking to see. Do we have an open circuit, meaning infinite ohms open line, or do we have a closed circuit, meaning low, ohms right and maybe in some cases in some rare cases I may use a ohm meter or a maker or a high potentio meter high pot, as it's Called to measure the breakdown of say, compressor, windings or motor windings over time in comparison to ground. So I may do that from time to time, but I'm not really looking so much at the ohm value. The ohm value doesn't doesn't matter as much to me all right, and so that's when it comes to when it comes to again this whole point of using a multimeter in a way, that's practical, that's what I'm encouraging is understanding what the limitations are.

What are some other limitations? Well, some other limitations are what happens if one of these meter leads is just out just a little bit, and so I'm reading not no voltage, because I just have a have a loose meter lead right and if I'm only going to trust that one reading enough To make a full diagnosis on the unit, I could I could get a wrong reading. I mean heck. My meter could be broken. I could have a situation where I'm reading zero volts.

I could have a failed meter. How do I know that? Well, I'm gon na use some common sense to assess everything. That's going out the equipment visually, I'm gon na look I'm gon na I'm gon na smell, I'm gon na I'm gon na I'm not gon na taste like I don't I don't do any tasting, but I'm gon na use my senses first and I can get a Lot of information out of that equipment before I'm just relying on my eager to make that diagnosis, because every tool has some limitations, some other limitations. I see a lot of guys who will say that they don't have, for example, a short circuit like in a compressor, they'll say: oh hey, I owned it out, it didn't have a short well, it may just be that you didn't have a great connection.

You didn't have a great connection on the on the ground where you were reading the ground or to the suction line. I usually, you know scratch a little spot on the suction liner on the discharge line, to read a shorted compressor. But if you don't get a good connection or you don't get a good connection to the terminal, even I mean maybe your. Maybe your meter lead slipped a little bit or there was a little carbon buildup that can do it.

It can also be inside the compressor, because when you don't have that dynamic current, when it's not currently functioning, it's not currently drawing current nothing's moving, it's all still in there and if you think of inside a imagine, inside a compressor, for example, or inside of a Motor any any type of device that's designed to move when it's still there's not going to be as much opportunity for a shorted circuit to bump up against a piece of metal or to or to short out as it is. When that thing is attempting to turn or attempting to move once it starts to move, you can very easily short out where, when it's still, it may not actually be actively shorted enough for you to measure with a simple ohm meter, and especially since your own meter Is powered by a 9-volt, a simple 9-volt battery and it really doesn't do much to boost up that boost up that voltage. If you take a you know, two leads of an ohm meter and you can touch to your fingers. It's not gon na shock! You! If you use a mega ohm meter or a high-potential meter, you'll you'll see that a high pot, like I always called a high potentiometer.

I think my instructor at school used to call it that, but you used something like that. It uses very high voltage and it's gon na be much more likely to you know, read through some oil or through some carbon buildup or whatever, and tell you for certain. If you have a short now again careful here, don't get the wrong idea. I've done a podcast and compressor diagnosis.

I'm not recommending that you use in May here on every application. They don't work right on Scrolls there's some limitations - it's not always even safe to use them. So I'm not telling you to use it. But what I am telling you, what I'm pointing out is not that you should use a different tool and pointing out that the tools that you have the tool in your bag has limitations and your multimeter and no tool so much so probably as your multimeter no Tool should you question as much as you question your multimeter, which comes down to simple things like making sure that your that your probes are in whenever I'm going to read a circuit for resistance.

I always you know, take the two leads and I touch them together to ensure that I have a path before I before I proceed. If I have am reading voltage I'll often check to an area that I know or assume that I have voltage first, that I have a potential between those two different points, just to make sure the meter is working good and then I'll go to an area. That's a more critical test point, so that's that's being thoughtful about how you use how you use your meter. So now, let's talk about actually measuring measuring voltage, so we have we time again.

We have the dynamic circuit where everything is operating versus the circuit, where it's not so. What's an example of a dynamics, measurement of voltage, a really good example would be measuring voltage on a running condensing unit or on a running packaging and whatever you have a system. That's running and you measure voltage on the bottom or on the top of the contactor, so you go between the two between the two legs between l1 and l2 and you place your meter leads on there. You have it on the Volt scale and you place your meter leads on there and it reads whatever it rates 237 volts say: well that tells you something that tells you that this is the potential that's present, even with the circuit under load, which is very useful.

You compare that to the voltage when it's not under load and you can calculate the percentage of voltage drop and you want to see with that particular measurement, no more than three percent differential between under load and not under load. Now that doesn't count under lock, rotor amps, because it will, it will jump down more than that and when it's under lock rotor when it first starts, but on a running system, you shouldn't see more than three percent on a typical typical application between what it is With no load on it, meaning with the contactor open between l1 and l2 at the bottom of the contactor, and once that contactor is pulled in that's a dynamic measurement of voltage, and that tells you something you know with the system running about that system. Well, what's another one well again, when we're using a voltmeter we're reading for a difference, we're checking for a difference in charges between two points? That's really what a voltmeter is doing, let's slow down and say that again, when you're using a voltmeter. I say this all the time.

But again you got to get this in your head: we're using a voltmeter you're checking for a difference in charges between two points. So imagine you're looking at a contactor right now, just imagine a contactor in your head, we'll make it a single-pole contactor, just a simple residential single pool contactor. So on the left side, there's that solid bar! That's not a contact point. It's not a switch just solid and on the right you have that switch right, so you've got a set of contacts that they go in and out all right now, with that contact pulled in instead of reading across the two bottom terminals, which would be l1 and L2 line in read across the switch so on the top right from the top right to the bottom right with the volts with the voltmeter, when, if you read whatever it is that you do read on that voltmeter and we're not talking about you know, like you Know under uh under a volt you know like I use sometimes you'll read, you know, half a volt and that could just be induced voltage like right now.

I've got my meter on and I'm reading you know point zero, zero, two volts just out there and in the atmosphere. So but if whatever you read across those those two points across that switch, that is the resistance that shows you demonstrates the voltage drop across the switch, which shows that the switch has resistance. So you could you do that with a ohm meter? Could you do it with it with the circuit de-energize and do it with an ohm meter, so I just switched it here with an ohm meter. I'm gon na push this one in right here and it's showing point 1 ohms right.

I could do that and that will show me what it's reading with it de-energize, but that doesn't take into account something I'd like we early talked about the light bulb on most conductors. I don't know if it's every maybe all conductors frankly but and most conductors at least I know for sure, as you heat them, the resistance increases, and so, as you add, more resistance, you're also going to increase the voltage drop. So the difference in charges will be greater when they're hot than when they're cold and so with a set of contact points that set of contact points is cold right now, because it's D energized, it's not under load right, but as soon as those contacts pull in. If there's resistance in this contact points where they're all nasty and gritty and gross as that, as those contacts heat up, the resistance is going to increase and as that resistance increases, I'm going to see that as an increased voltage across the switch and again.

This applies to dynamic, a dynamic situation, a situation where electrons are moving. There's current, there's amperage. The thing is running right: I'm gon na swatch as those contacts heat up that that voltage drop increases and so what I'm gon na measure across. That's that switch contact with voltage is going to increase as those contacts heat up, and that can show me that I have contacts that are failing, which in fact is a really good test to do now.

I'm not going to tell you what the pass/fail is on a set of contacts. I don't haven't done enough studies of contacts to tell you what a pass/fail is, but I can tell you that it is a good way to tell you if the contacts just look bad or whether or not they actually are creating voltage drop just measuring across there. Because again, if they create voltage drop, then you will read a difference of potential between the top and bottom of that of that closed contact that actually has dynamic current going through it and traditionally technicians would say well the way to do that is to measure across The top and bottom of the of the contactor. Well, you could do that and compare the two voltages or you could just read across and whatever voltage is.

There shows you a difference in charges which means voltage drop.