What is a Contactor? How does a Contactor work?

Posted: 2020-08-15 | Updated: 2020-08-16 | Read Time: 6 minute(s)

Recently I had to replace the contactor on my air conditioner after the last one had a burned wire on it. I discuss the parts of a contactor and how it works. Check out the video!

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Video Transcript

what's going on fellow engineers this is Kenny and thanks for checking out the Almost Engineer Channel and in this video I'm going to talk about a contactor this thing right here and how it works stay tuned [Music] alright so this is the contactor that I took off of my HVAC unit and this is the old one so I just wanted to talk about what a contactor is and what it does and how it works and so there are some elements on here that are not exactly right with a modern contactor this one is probably original to the HVAC unit that I have so there are some differences that I notice between the new one and the old one alright folks so I got my new contactor which is this one over here and my old contactor which is this one here for the most part they are pretty much the same the screw on this one actually I had to screw it all the way out to get the lead out of there so but there are some significant differences that I'm noticing so on the top of this one actually you stick the wire in whereas this one had a clamp that you put a connector on it and then you put that connector around the screw head so the top is essentially like the bottom now where you stick the whole wire in and then you screw to clamp it down all the way also the same number of pins here looks to be there's eight on the bottom and there's eight on the top here I only had I believe it was two wires here and this one also is enclosed so as you can see you can see the coil on this one both sides so but you can on this one and the reason being is somebody actually took the counts that hey bugs can actually get into this thing and cause problems so what they do now is they actually seal it up entirely so all this mechanical stuff like this right here is not exposed to the elements however you can take these two screws off and this play to come up and then it will look just like this inside underneath this cover here so that's the difference between the new contactor and the old contactor and so with this particular contactor unit so we'll start off with the label of course and here you'll see is rated for 25 amps and it's also a 24 volt coil and so the contactor that I put on is actually rated for 30 amps but it's also 24 volts and so what the amperage has to do is that it has a maximum capacity you know you see it as 25 so if you try to push 30 through it more likely you'll have a problem and I think that kind of helped in some cases the failure of this one and so if you see right here where this screw is you'll see this plastic here is actually burned and cracked it actually broke off what happened there was it looks like the wire on it actually broke burned some kind of way I don't know if something got into it and caused it to short out or what the case was but this is the connector that was on it after the fact from the wire way it burned off at so and as you see this screw is actually brown so I don't know if that is the indicator of the problem that was going on with it because it should not have been brown it should be fight the rest of these you know silver we're not so just a walk overview of everything so on the bottom here have pins you can have these push connectors that go on these pins here at the bottom then you also have these two terminal screws and so you can stick the wire in this gap here tighten the screw down same thing on this side and then on the top it's a different setup because they actually use these connectors that go over the screw and then you tighten screw down on the connector instead of sticking the wire directly in so that's that side and this is what is known as a single pole breaker and there's also a thing called a double pole breaker so the pole is the thing that actually moves so this one here is not seized up it does move but it only has one pole which is this side so this right side here as you see there's a metal bar that goes from top to bottom that means this side is always hot this side is the side that switches so we turn on the AC U and it this goes in and it connects the bottom which is where the power comes in that to the top which is where it goes out to the compressor and the fan on the condenser unit and completes the circuit so sue Evans so fan is running but there's no I don't hear the compressor running too and so that's how that works now how does this move back and forth well on this side and on this side you have these two connectors as well these since this is a 24 volt coil these connect to the 24 volt wires that come from the inner handler that is on the building interior so when there is a call for cooling the thermostat connects the wires inside of it and that signal goes to the air handler the air handler triggers that same since that signal out to the condenser through one side and then back out the other therefore you complete the circuit and when you complete the circuit on here this pushes in and completes the 240 circuit so if you ever heard me discuss about relays before this is essentially the same concept as a relay you have a voltage of one type in this case would be in 24 volts controlling a voltage of a higher type which in this case is 240 volts that's 120 on the Left 120 on the right which equals 240 now this one may or may not say it I do not believe it does but it is designed for 240 but it doesn't say it the unit itself says 240 the actual conditioner unit says 240 on it so and then once you remove the 24 volts so the thermostat says hey I've reached the set temperature shut off so that means the thermostat disconnects the connection between the air handler and it and so as a result that same connection is also removed so the incoming 24 volts is removed from here and thus there's nothing on this side to go back so this connector in the middle here will spring up and there is a spring underneath it as you can kind of see right there there's a spring there and so that comes back up to disconnect the connector connection between the top of the bottom so that covers how a contactor works hopefully you've learned a little bit and are able to apply this in the future if you have any questions about the contactor or relay please hit me up and drop a comment in the comment section below also please check out me on social media on Instagram and Twitter at almost Engr and check out my website the almost engineered calm [Music]

Published: 2020-08-15
Updated: 2020-08-16
Author: Kenny Robinson, @almostengr
Category: Handyman
Keywords: contactor, electrical engineering, electricity, hvac repair, hvac components
Video URL: https://youtu.be/1GeZH9MO16E
Read Time: 6 minute(s)