How to know if limit switch or fan switch should have continuity. #maintenancetech #limitswitch

this year is something I always struggled with when I first started working on air conditioners or heaters or furnaces or anything like that I couldn't tell the difference between a limit switch and a fan switch I had no idea there was even difference to me they both looked the same I couldn't figure a difference I didn't know there was an actual difference so for a long time I had a time a hard time trying to figure out what was what was it supposed to be open did it did it need to have continuity did it not I really didn't know and I didn't I didn't study HVAC or or fixing heaters in a score or anything like that I just learned online and I never never learned this part so today I want to share with you guys if you're an HVAC uh technician this is just basic really basic really easy but this is mostly for maintenance guys or people that handyman that work on furnaces or heaters stuff like that uh now the first thing I want to say is if you're not comfortable there with the electricity call Professional and if you're going to work on this it's always better to pull the disconnect or uh turn the power off to the unit you don't want to be working on any of this while it's energized so that's just something I wanted to share before before I go any further but now let's get into what what I'm talking about here with these two now they both look the same when you see them it's really hard to tell what's a limit switch what's a fan switch what's the difference what do they do where do you find each one now we're going to start with the fan switch the fan switch is is always open when it's it's not doing anything it's open so if I put a multimeter here and I'll put it on just on continuity you'll see that it's it's an open I'll do it down here that it's open it's there's no there's no continuity to it so that's that's a once I meter on continuity and of course it's open so this is always going to be open when it's when it's not in service or doing anything what this does well the first thing I want to say is how do you know if it's a limit switch or a fan switch well you're gonna read the plate or the sticker or whatever on this one it's kind of hard to show on the video but when you see the numbers here I'll try to make it to where you guys can see it 'll be hard so that right there says f120 so f means fan so this is a fan switch this is not a limit switch this is a fan switch and the 120 is at the temperature where it it ignite where it um what it does continuity where it connects so in this case we already tested it it's open it's an it's an F so it's a fan switch so this will always be open this is usually next to the heat exchange and and this this will this will will make contact which which will allow the fan to kick on once once the heat exchange is hot then it'll it'll let the the it'll turn on the fan it'll it'll have continuity to the fan now the way we're going to test this this and uh what I want to show you guys is right now of course we tested it and it's closed now what we're going to do I'm going to put a little bit of at 120 degrees it'll it'll it'll make contact so hopefully you can hear it I don't know if you heard that but it clicked now I want to burn myself so I got to be careful here um so now at the continuity of course this time now that'll that'll let the fan turn on so that's that's what that's what the fan switch does and it's always going to have an F the 120 degrees that that's where it kicks on so this is a fan switch this is always open when it's not in use now next we're going to look at limit switch now a limit switch is a protection that that heaters have that will cut cut uh energy to the circuit board or to the uh gas valve or or whatever so the gas sets off that means there's something going on either there's a restriction in the line the blower motor is not kicking on or didn't kick on or turned off or or dirty filter could cause this and they also go bad over time sometimes you just got to change them so this is exactly the opposite now this always is is when you're not using it is going to have continuity so this is normal this is normal this is what it's supposed to be so this is a limit switch they're going to have continuity now if there's an issue and the heat exchange area and and it got it overheated it's too hot something's going on like I said there's a restriction now I'm gonna do the same thing I'm gonna this this is well I want to show it to you first okay so as you can see there's an l which I was going to indicate living switch 140 so I had 100 140 degrees that's where it'll shut off and then that's a minus 40 that means that when it comes back to 100 it's going to kick back on so this at 140 degrees if it gets too hot and there there's different ratings for these so make sure that if you're going to change one of these you get the right rating um at 140 degrees this will cut out now I'm hoping you can hear it on the microphone so we'll do this with a lighter again so that now will not have continuity of course because um now it got too hot and that that cuts the uh continuity to it of course there's nothing going on now I can't put it on the table but as you can see the contacts are are not there's no continuity to these so once it dries once it cools down to 100 degrees which shouldn't take too long it will kick back on so that is a difference between a fan switch and a limit switch even though they both look the same you're thinking what's the difference that's a difference that's something that I had a really hard time trying to figure out when I was when I was doing this I couldn't find any videos I didn't go to school for this so nobody really taught me this I couldn't tell the difference you're gonna find fan switches next to uh where the fans at next to the US a heating element or a heat exchange and that's and that's what's going to let the fan turn on oh it's this one and the other one is the protection that's that's that's also going to be some of the package units stuff they're going to be next to the to the fan also but that's a protection for the uh for the system well I hope this video helps somebody out and um Good Luck

Channel: Maintenance Man Narratives

Views: 25,175

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Id: wtEjAqufHDg

Length: 7min 6sec (426 seconds)

Published: Sun Oct 30 2022