All right, so i want to talk about the ohm setting on the meter, because it's one of the ones that is underutilized and then when it is utilized it can sometimes be utilized wrong. So whenever you first look at a meter, if the leads aren't connected to anything, then on this meter you're going to get the dashes on this meter, it reads ol and that means essentially infinite ohms. So that's not saying no ohms, that's not saying zero. Ohms! That's saying: infinite ohms, which means that connect them together, you're going to get a very low ohm path so equivalent to zero ohms, meaning a very good path.

Anything in between is going to be a measured amount. We'll just do it on this one here just to show it so we have an open path. Then we connect it together. This one's not set up for the continuity ringer, but you see it's measuring a very low ohm measurement now so infinite ohms very low ohms.

But how do you imagine it? Does that measuring? How do you think it does it sends some electricity send some electricity? Okay, small charge, okay, small charge potential, yeah and you're right about that. So i want to show how we can measure this, because it is actually interesting. There are certain limitations to ohm meters and that's because they don't utilize a lot of voltage for their own test. It's a pretty low voltage, but you can actually find out what it is.

So what we'll do is i want you to take this meter here and put it to the volt scale. All right now give me the give me the meter leads hold them up to me. We're going to measure what voltage we're outputting from the ohm meter on this side. So this ohmmeter here is going to output a voltage, that's going to be measured on the other side and let's see what we get oh, we need to make sure that we are reading in the dc scale.

So right now it's it's measuring in ac, so change the setting. I think it's a blue button there to get it to go to ac all right. So what do we? What are we measuring here? Negative 0.8 negative 0.8 volts? Now, that's just because of the polarity! So if i switch it around 0.8 volts, so that's all we're measuring 0.8 volts, not a lot of voltage in order to test that now, let's flip it around and do it the other way and see how we see how we do so we're going to put This one on voltage now and now we're going to put this one on the ohm scale now again we're just using the meters we have around here in this in the class. Nothing super fancy here now.

I need to put this one to volts dc 0.53 volts. You see that very small voltage now. If we compare that to our fluke, which can put out up to a thousand volts, you can see how, with a mega ohmmeter or a ohmmeter, that puts out a higher voltage you're going to find shorts with that higher voltage. That you're not going to find with this more simple device.

So, if you're looking for something like a short to ground on a compressor, these aren't necessarily going to be your best bet now, if they find them, they find them and that's great. But that's why sometimes you're going to put your meter on ohm scale, you're going to check for a short to ground and you're not going to find anything with a simple multimeter in the ohm scale, because it doesn't have that voltage and that's where a mega ohmmeter With a readout comes in really handy, but let's go ahead and show so we've already shown. This is what it looks like when it's open line when there's infinite ohms, but let's actually do some measurements with it. We can use our ohm meter for a couple different things.

We can look at the opening and closing of switches. So let's say that i couldn't see inside this switch say the cover was over and i wanted to see if it was open. All i would have to do is measure from one side to the other, and i can see that we have an open switch now if the switch makes or closes now. I can see that we have next to zero ohms, so that's for a switch, but for a load a load is going to have a measured ohm amount.

So it's not going to be open, which is infinite ohms and it's not going to be closed, which is near zero ohms, it's going to be somewhere in between. So now, i'm going to measure across our magnetic coil. So this is our magnetic coil. Here one side connects here: the other side connects here.

This is just a very simple compressor. Contactor, these alligator clips are a little clunky. So now we have both of our meter leads connected to the ohmmeter and we're measuring 18 ohms. Now the question becomes: is that good or is it bad it's hard to know unless you had some sort of a rating that told you what the expected ohm rating on this coil would be, it would be hard to know in a vacuum what the ohm rating Of this coil should be now.

We know it shouldn't be open and we know it shouldn't be zero right, but what we could easily do is we could take another one off the truck and compare it to it now. If it's a different brand, it might not be exactly the same, but it's going to be pretty close, so that can give us a really good indication. Let's take a look at a 9340 relay another really common component in a system. You can see here that it shows an open path from 1 to 3, normally open and then normally closed from 1 to 2..

If this is functioning in its normal state, how it should be because it's not doesn't have an energized coil. We should have an open path - infinite ohms from here to here and a closed path from here to here. So, let's see what we get have an open path where we would expect an open path. We have a closed path where i would expect a closed path and whenever you're, owing out a switch, that's what you're looking for open or closed another term, for that is continuity.

When you have continuity, that means there is a path when you don't have continuity. That means there's no path: okay, but we're going gon na look at the coil again. So here we've got this. It's covered in.

You know this white plastic here. But if you look really carefully, you can actually see where the little copper wire runs in and then it connects to these points right here. You can actually see the copper running up through this little channel to both of these connection points, and so these are the points that are the coil, because the coil is a load. It's going to have a measured resistance.

So, let's see what we got wow on this, it's auto scaling to 0.4 kilo ohms, so this is measuring at if we move the decimal over from k, ohms thousands of ohms, we can see that this is actually measuring. What would that be? That would be 416. 414 ohms now that seems really high compared to the other coil. But again we would have to compare this against another 9340.

Another similar relay in order to know so, let's grab another one, so we've got one over here at our test board. This is a little older model, so we could have a little bit of variation, but let's just see this is what we got to do in real life. Wow, significantly different resistance, very interesting. Let's try a newer one 15.7 ohms, so these two are actually pretty close to each other.

So do we think we have a bad 9340 right out of the box? Is it possible that that's the case? The next thing to do would be just to energize it and see significantly higher. Now again, you can see it is a different brand. This is a mars, the others, i believe, are white rogers, so we'll actually energize it and see if it functions or not with the designed voltage, the 24 volts okay, so you can see we have 25 volts. I did not hear the switch click over on this.

So this should now be closed and it isn't. This should be open and it isn't because we have an energized, 24 volt coil, so sure enough that coil measured open and it is actually open. I mean it's not open, but it's measuring very high ohms. So let's go ahead and test it on one of the ones that showed as if it was working and just see.

If we get a different result test to make sure our voltage just went off now, yep voltage is off all right. So we're going to swap this bad boy out with a different one. This is a very surprising demonstration, given that i had no clue that that thing was bad when i grabbed it, but that actually makes it that much better okay. So now we're going to apply 24 volts to this coil, the one that measured ohms that were closer to the other, and now i heard it click that means that this switch that was closed should now be open, and it is - and now this one that was Open should now be closed and it is go ahead and hit that switch and watch what happens as soon as we de-energize that coil now it goes back to normally open.

So that's exactly what it should do that other one that looks brand new and even threw me off, because i was not expecting it to be filled out of the box - has a coil that, while it's not technically open, it's measuring far higher ohms than it should Measure and that's what's resulting in the issue, this video is going to turn into a a comedy of errors, so i pulled this out and actually in the in one of the views, you probably would have seen it on this side. You know this is just the switch ratings which that's all normal, nothing abnormal there, but here our coil rating is 120 volts. So of course it didn't pull in with 24 volts make sure you pay attention to what you're taking out of the box. The coil is not bad, it's just rated for 120 volts, which is why the resistance of the coil is much higher when you're comparing apples and oranges.

Sometimes the measurements don't add up, which is kind of a funny thing, but either way we demonstrated here the opening and closing of a 9340 relay and the measurement of the resistance across it. Another quick thing to mention here is that you never want to measure resistance in ohms on an energized circuit, and a lot of people will get confused by this, because they'll see that i'm energizing the coil and they'll think well now it's energized well when you're energizing, The coil on a 9340 or on a contactor like this that doesn't have anything to do with these switch parts. So this the switches are not connected to this bottom coil part. It's the same thing with the contacts on the contactor this part here.

These lugs are not connected in any way to these, so i can measure with an ohm meter across the switch portion so long as i'm not connecting it to the coil portion and that's okay to test. But you never want to take your ohm meter in the ohm scale and connect it to an energized circuit because you'll damage your meter so on this one the coil is actually serviceable and replaceable. It sits in like this and then these fit on top and then the base plate goes on like this kind of holds it all together, squeezes it all together, but you can see how that portion down. There was not connected in any way to the switch portion, but since we're just taking some ohm measurements on some things, let's just keep doing that.

So with this, because you have an interchangeable coil, i would have to have the coil back out in order to look at it. So let's take that back out again. So here's our coil it's a little hard to read here, but it says 120 volts at 60. Hertz, so this is another 120 volt coil.

We can oh mount the coil independently. Now you never want to energize one of these coils without being connected, because it will cause it to fail. We can see that this one is 203 ohms. If there's just air inside here without it actually drawing in that can cause it to over amp same thing is true with the reversing valve solenoid, you only want to energize these when it's actually on its assembly, so now we're going to fit it back together.

We're going to be a real pro at this now that i've done it a couple times, i'm sure the real mechanical wiz, and now we can own out the switch, and this is an example where we can't see the switch. We can't see the contacts, so we would check to see okay, it is open when we energize it with 120 volt coil. Then we can make sure that the switch actually pulls in and then we would read near zero ohms across the switch. In this case.

It's three phase, so we've got three sets of independent switches all right. Let's do some more neat things. We got a float switch here and one kind of fun fact i did a. I did.

A facebook live video on this once, but on these rector seal float switches, they come with the conductors actually attached to staples on the outside. So if you want to test the thing when it's on the shelf before you even purchase it, you can actually test on these staples. You normally wouldn't do it with these weird meter leads all right so now we're attached there. When the switch is closed.

You can hear it beeping, so there we're just using a continuity test to prove that the float switch is actually working pretty simple, so it goes from infinite when it's not beeping to continuity, which is a closed switch when it is let's check on some heat strips Now again, whenever you're measuring on anything where you're trying to test for open close continuity, whatever you want to disconnect it, because otherwise it could backfeed and we don't want to measure a back feed. We don't want to measure a unintended path. That's possibly coming from the other direction, so we're going to measure through one of these strips all the way through and see what we get so i've disconnected it now so now, there's no way there can be a backfeed and i'm going to measure 11 ohms. Now a lot of people would assume - because this produces a lot of heat, that it would be very high resistance, but it's actually the opposite when you think about ohm's law, lower resistance equals higher current, because this is a resistive load.

You don't have that additional adductive reactance that shows up in inductive loads. So when you see a low ohm measurement like this or what is comparatively low, that means it's going to draw a lot of current and sure enough. At 240 volts, a 5 kilowatt heat strip is going to draw about 20 amps. So what we just measured is a load, a high voltage load, we're looking for a measured resistance.

Same thing is true on a reversing valve solenoid, so you shouldn't see completely open. You shouldn't see completely closed because it is a load. It's designed to do work. It's an electromagnet, see what we've got here.

16.3 ohms now again. Is that good? Is it bad? Well, it's not zero. It's not infinite! So that's good. Is that what's appropriate for reversing valve solenoid, you would have to either have the spec off the solenoid or compare it to another identical model to know for sure, in the grand scheme of things that looks about like what i would expect for 24 volt electromagnetic coils, That range is what we seem to be getting a lot of, so i wouldn't suspect that we have a shorted or open.

We know we don't have an open, but i wouldn't suspect that that's shorted, based on that measurement, primary and secondary of a transformer. So there's two distinct coils. You have one coil on top one on the bottom. The one here is your low voltage side, which is your secondary coming out of the transformer.

This side is your high voltage going into the transformer, and we have multiple taps here, but mostly what you're? Looking for when you check a transformer, is you want to see that it's not open, because when they fail, they're generally going to fail open and you can actually learn a lot by which side failed? If the secondary failed, then likely it's a cause by the secondary? Something is shorted in the second area that caused the open or the short and the secondary of the transformer. If the primary is what's open, then often it could be a power surge lightning strike, something that happened on the primary side that caused the transformer to fail. Now on this transformer you've got to look at it kind of know what the colors mean. So white is common and then, if we were going to use this on a fan coil, we would use the 240 volt most likely.

So we're going to measure between white and orange to see are we open shorted or do we have an appropriate measured reading or what we would think to be an appropriate measured reading, and this is on our primary? This is going in so we've got 102 ohms going in. If i want to know for sure, compare it against another transformer coming off the truck, but it's not shorted and it's not completely open. We have a measured resistance secondary now. Don't let the beep concern you, because we still have a measured resistance just because it's beeping, this meter has a point at which it starts giving you that kind of continuity, beep.

That doesn't necessarily mean it's shorted. You still see. We have a measured secondary resistance, so i'm not i'm not concerned with this. I think this transformer is probably just fine chad wired up relay to 120 volts.

If we back up here, you can kind of see it's coming directly from our incoming power. Here we go yeah right there, 120 volts to the coil flip the switch. It's amazing how 120 volt coil relay works best when you put 120 volts to it. So there you have it a lot of different ways.

You can use an ohm ohmmeter and also pay attention to your data tags, thanks for watching thanks for watching our video, if you enjoyed it and got something out of it, if you wouldn't mind hitting the thumbs up button to like the video subscribe to the channel And click the notifications bell to be notified when new videos come out, hvac school is far more than a youtube channel. You can find out more by going to hvacrschool.com, which is our website and hub for all of our content, including tech tips, videos, podcasts and so much more. You can also subscribe to the podcast on any podcast app of your choosing. You can also join our facebook group if you want to weigh in on the conversation yourself thanks again for watching you.

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