How To Check Power At Thermostat - Furnace & Ac Won't Start - Finding Loose Electrical Connection


Hey, my name is Ben. Thanks for stopping by today, we're going to be talking about troubleshooting a loose connection or a loose electrical connection in a HVAC system and the symptoms that we're experiencing here are that the thermostat keeps losing power. And we know that because the thermostat that's installed here is a nest thermostat, which uh uses power steeling. And or the common wire to get its battery charged up and make it operate properly. Now, if you had a thermostat that had batteries in. It, you may not notice anything at the thermostat itself. But you may notice that the equipment is just not working, even though the thermostat says that it is.

So sometimes when we have intermittent issues like this, where we're completely losing power and what I'm going to do here in a minute is we're going to actually look downstairs first, and I'll show you we're in an attic by the way in case, you didn't, notice, but I'm going to show you how to check for power on the thermostat, terminals and that's. What ultimately led me to be up where I am now, so I'll show you what the problem was here really quick, and then hang on, and we'll, uh, talk about how to check it at the thermostat in just a minute. Now, obviously, before you go looking in your HVAC equipment, you're going to want to make sure you disconnect power, or if you're going to work with the power on make sure you know what you're doing, because there are 120 volts high voltage. Sometimes 240 volts be really careful. Don't do this unless you feel. Comfortable doing, so these intermittent issues can be really difficult to troubleshoot and that's why I just wanted to kind of point out a few things to look for in your furnace itself.

So right now the power is turned on typically there will be a switch adjacent to your equipment. This equipment is pretty old you're, not going to see this exact setup, but this is the concept still applies. So we follow our main power wires coming in here. And you can see that they're spliced right here. These are the. Connections that are the field installation connections, the rest of the connections inside most furnaces are done at the factory.

So these are oftentimes the most suspect for having issues. Now, if we look closely at this wire nut, right here, what I noticed right away is that there was some disc coloring happening on the insulation of the wire that goes to the actual equipment now I'm going to turn this thing off again here, and I'll just take this off. So you can see that we have it fixed now. So when I first looked at this thing that stranded wire was wrapped around the solid one, but it wasn't really engaging in the threads of the wire nut and that's a problem. Because if you don't get the threads of the wire nut around, both conductors oftentimes it'll be still wrapped around there, but it won't be actually making a proper connection. And when you see signs of heating on your conductor or on the insulation next to it, you know that there was a little of arcing that was occurring. So.

What alerted me to this right away was that as I pulled the cover off of this electrical compartment, it right away the power actually came back onto the system. And I was getting voltage at my thermostat, terminals, and we're going to talk about that. Some more here, too I'll show you down on the actual thermostat, how we can check if there is power coming in to that thermostat and that's going to be one of the more important or easier troubleshooting steps before you necessarily look into what's. Actually happening at the equipment. Now that we're here, though I will just show you that we have voltage now at our thermostat terminals.

So our terminals are exterior on this particular one. These will normally be mounted on your control board or something similar now we're going to check between the r and the common so r. And the c they'll typically be marked, which is typically going to be the red wire and the blue wire we're testing in volts alternating current. And you can see that we do have 30.

Volts showing right there, normally it'll be closer to 28 volts, but 30 is still fine, so we're getting proper voltage coming out of our unit now. And we know that we have power to this system. So everything should actually fire up just fine now I'm going to put this cover back on there. And then I'll see you guys downstairs in a minute. Once I make my way back through the attic and down through the access hole and over to the thermostat here we are at the thermostat. You can see we've got our. Electrical meter set to volts alternating current I'll link to this electrical tester in case, you guys are looking for a good general purpose, electrical tester.

But anyway, what we're looking at here on the thermostat? You can see we have our ray WC, real quick, I'll run through what their purposes are. The r is our 24 volts coming from the thermos from the equipment transformer. So it should be 24 volts. We measured it upstairs. It was 30 volts, and then it's going to the thermostat is going to take power.

From the r and apply it to these other terminals to basically make the system work. So from the r to the g is going to bring on a fan r to the w1 typically is going to bring on your heating and then r to the y is going to bring on your air conditioning. So the common wire here is actually just basically like a neutral. And that is going to allow the thermostat to draw power from this, uh, power supply on the r without turning on any equipment.

Now, the nest can do power stealing. So even if you don't. Have a common wire, the nest will still work by applying a tiny bit of current from the r to the g to the y to the w, uh, all at the same time, but not enough current to where it'll actually bring the equipment on. You can see right here.

The nest thermostat, even tells you what all those different terminals are for the power. The fan, the cool, the heat and our 24, volt common. Okay. So we're going to test the voltage now that you kind of understand the basics with that, um, like we said, the r is going to be. Our 24 volts or 20 or 30 volts.

In this case is what it's actually putting out if we check from the r to the common, you can see we're getting that same 30 volts that we're getting upstairs. So that means that we have power to the thermostat, and therefore the thermostat should now be able to function properly by taking the power from the r and applying it to the different terminals. Now you can also measure, uh, power, typically anyway, from the r to your other wires as well. See, if I can get there, 30. Volts from the r to the g, the reason we can sense power from the r to the g is that there's a relay that is basically a big coil of wire or a tiny coil of wire that is going to allow power to pass through to here. Well, it's, actually the other side of the common. If we measure from the g to the common right now, there should be no difference because essentially these are the same thing right now you can see.

The difference is basically nothing. So if you don't have your common wire, which is fairly. Common to not have it common. Then you can measure from the r to the g or the y or the w. And you should still be able to sense whether you have power at your look at the location where you're testing if that doesn't work for some reason you can also check from the r to ground like if you had the metal frame of an electrical box nearby, you could check from the r to ground let's say that the screw went to an electrical box that was metal.

We would be able to see voltage there. So just another. Way to check it, just in case, you run into that.

So now that we have power let's, go ahead and take our thermostat stick that back on the wall. I believe it was totally dead. But now that there's power here it should come on and start to charge. Now that that loose connection has been repaired up at the equipment. We restored power to our thermostat. And we verified that with our electric meter.

This system should be good to go we'll test it to make sure that it's all working properly. So hopefully that. Gave you a good idea of what to look for a loose connection and also just for testing for voltage at your thermostat. If you want to keep troubleshooting, though I'll put a couple of videos here on the screen, and we can continue to work through figuring out what's going on your uh, your system, uh, in just a few seconds. So go ahead and click on one of these videos, and we'll see you over there. I don't know where you guys are from, but uh in our area, southwest Minnesota.

This sound coming from. That huge flock of birds up there is one of the most identifying sounds of spring, and it's, amazing they're. So noisy.

Dated : 19-Mar-2022

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