In this episode of the HVAC Mentors Podcast, host Mike educates aspiring and current HVAC technicians on the fundamental difference between voltage and amperage and how each is measured in the field. He explains that voltage is the potential difference (the "push" or pressure) between two points in a circuit, while current (amperage) is the actual flow of electrons (the "work" being done). Using water‑bucket and waterfall analogies, Mike illustrates how voltage exists even when no current flows and how a closed switch shows 0 V across it despite being live. He discusses practical troubleshooting: a full voltage reading across an open switch or fuse indicates a live circuit, whereas 0 V across a closed switch is normal. He emphasizes the proper testing sequence—verify voltage across a component, then measure current (using an amp meter or clamp) to confirm equipment is drawing power. The episode concludes with three key takeaways: verify the push (voltage), understand that voltage is measured across a circuit while current is measured through it, and recognize that current is where the work happens. Listeners are encouraged to comment, like, and share the episode.
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Welcome to the HVAC Mentors Podcast. My name is Mike, and if you are the new guy, an aspiring technician, or just thinking about maybe getting into the trade, if you don't feel like you know enough and you want to brush up on your knowledge, or if you're looking for resources to pass along to the newbies in your own life, this is the show for you. On today's episode, we're going to be talking about a very important topic, which is voltage versus amperage. We're really going to nail down what it is, what the difference is, and what you're actually measuring when you pull out your meter and try to diagnose a system. So if you have questions or suggestions for the, for the podcast or for future episodes, please leave those in the comments, but definitely like and follow and pass this episode along to somebody who you think it could help. So anyway, with no further ado, the The question that we're really thinking about here is what are we really measuring? Okay, you pull out your multimeter, you set it to voltage, AC or DC for that matter. What are you really measuring? A lot of times, especially at first, we think about voltage as that's the electricity, that's the power going through the wires, but really it's technically not. Voltage though is what enables the current to flow, but we're not actually measuring current. Instead, what we're measuring is the difference from one point in the circuit to the other. Think about it this way. If you have, if you have a waterfall, the reason the water goes down to the point at the bottom is because gravity has created a point where there is less water. There is a lower, really it's the energy in the water. It's the, it's that drop has lowered the potential energy. In the water, and therefore the water falls to the lower point on the other side of the falls. We'll get more into that in a moment, but I think we need to really nail down 2, 2 questions. That being, what is voltage and what is current? It's important we understand the difference here so that we can understand what we're actually testing. So as far as voltage goes, we can kind of think of it as the push. Okay? It's the pressure waiting to move electrons. It's a potential energy. It exists even When nothing's flowing, it's, it's always there in the elect— in the circuit, and it's just waiting for a switch to close so that again, it can, it can allow the current to flow. And the thing is, there's always a difference between 2 points if you're measuring across the circuit. If, as long as we're energized, as long as we have voltage flowing from the source, or rather, if we have current flowing from the source, we always have a difference between 2 points. If you're measuring and you get no difference, either A, you don't Have power, or B, you are measuring across a closed circuit. So then that brings us to our second question of what is current? And we could think about it as the volume of flow. So again, just to think about it as a river, you know, whether it's a small stream that's just barely seems like it's moving, or if it's a rushing river or like the Mississippi or Ohio River where there's just tons of potential energy stored in that water just flowing across the country. Either way, there is a volume of energy moving. And the electrons in that are actually flowing and they're actually like kind of jiggling back and forth. And that's what is doing the work. It's, it's the current that's actually turning the motors and making the heat. It's the current that you're actually measuring. And that's why we need voltage and current. And they're often Kind of, they're measured together and they do work together. But in order for current to flow, it needs a complete path to exist. Okay? We're measuring current through the load versus volt— or through the circuit, whereas voltage, we're measuring across the load or across the circuit to find where maybe we have an open circuit or an open switch or a failing switch. So just to carry the water analogy further, imagine you have 2 buckets on a shelf, okay? One bucket is on the upper shelf is full of water. There's a hose attached to the bottom leading into the bucket on the next shelf down. We could say that if we put water in the top bucket only, and the bottom bucket is empty, that we have a difference of potential energy between the top bucket and the bottom bucket. Okay. Let's say that we have a ball valve in that, in that hose so that the water isn't going to leave the top bucket. and flow down to the bottom. Okay, as long as that valve is closed, water isn't moving, right? But the pressure difference still exists, and that's when the meter reads full voltage across the blockage. So in the field, full voltage across a switch or a fuse equals a live circuit, which usually means you found the open point in the circuit, whether it's a broken wire, loose connection, or a switch that has failed open. So if you If you move that bucket to the next shelf down to where the amount of water in both buckets is now equal, you would measure 0 volts because the amount of water contained in both buckets is now the same. You're not going to, you don't have a difference in potential energy. And since energy wants to flow from where there's a high concentration to where there's a low concentration, both buckets being equal, energy is not gonna move. So if we measure 0 volts across the circuit, That means that energy is either A, it's moving in equal proportion to the rest of the circuit, or B, there is no energy actually flowing. So in other words, you might be measuring across the, you know, 2 points of the same circuit, a live wire from one end to the other energized. You're going to measure 0 volts because it's the same potential energy. That would be measuring bucket A against bucket A. It's not— Any different. Uh, that's why we need to be careful that we're measuring across the load to both sides, across the circuit, so that we can actually determine the potential difference across the circuit. But either way, both points are live at 120 volts, but your meter compares them and finds no voltage. That, that tells you that maybe A, you have a bad reference point and you're measuring on the same part of the circuit once again, or B, you have a failure. So a closed switch passing current. reads 0 volts across it. And that's very confusing to the beginner because you would think, oh, 0 volts across my switch, that means there's no power. Well, no, it, it, this, the electricity doesn't know if that's a closed switch, if that's another piece of wire, if that's, you know, a piece of the cabinet that got grounded. It just knows that it's got a path. So of course it's 0 volts across the closed energized switch. And basically what that means is that Both sides of that switch share the same pressure. So what are kind of the key things that we need to take away from today's lesson? Well, the one thing is that when you're testing, we wanna verify the push. We wanna make sure that there is even a potential difference there at all. If that's not happening, then there's no flowing. But then we verify the, the flow. That's why, like, when testing a compressor, you might actually verify that you're getting voltage. to the compressor, and then you're going to take an amp draw because you want to verify that you're getting power at all. Then you want to verify how much power now are we getting. Voltage, number 2, is measured across a circuit while current is measured through the circuit. A voltmeter is always gonna compare 2 points. The reading is the difference in potential from one point to the next. And then finally, the current is where the work's happening. So where voltage is the, the potential difference that allows the work to happen, current is the work actually happening. And that's where you're going to use your amp meter or the amp clamp, which is going to tell you what the equipment is actually doing. Hey guys, I hope that was helpful. And again, if you have any questions or any further comments, feel free to share those in the comments. Like and definitely share with somebody who— This might help. That aside, I look forward to sharing with you again on the next one. Have a great day and thank you for listening to the HVAC Mentors Podcast.
