How to wire the Honeywell fan and limit switch for the gas or oil furnace 

please do more like this, thanks this is what new techs need

thank you for posting this. your switch schematic was a helpful starting point to troubleshoot my furnace. My problem was an open stranded conductor connecting the line side, and a blown 25v transformer.

I know a lot of people probably have no exposure to old furnaces, but I can’t help but be amazed that there’s people that would have questions on one of these fan limits

Great video and I also would like to give you a little history on this fan limit control. This fan limit control is the reason why engineers in the HVAC manufacturing industry designed the secondary ECO one time use limit. We found this fan limit control to have devastating failures throughout the United States. At times the heat sensing spring would lockup ( caused by rust and A coil drain pan leaks) causing the fan to never come on or limit to open. So as you can imagine many houses burnt down and people lost their lives. So my suggestion is if you ever replace one of these fan limit controls an a ECO limit is not in place, add one . Also note this fan limit control comes in two sizes short and long ( make sure you know the one that is required). Also I wanted to correct you I believe you misspoke,you said this mounts inside the heat exchanger , it does not ( it mounts to the furnace cabinet sensing heat from the outside of the heat exchanger). Great video and keep them coming. Y'all stay safe out there.

Very helpful. I'm replacing mine on my 1965 model furnace. As usual, the new one is a little different....

My burners would come on and run for 1.5min then shut off, then after cooling for 30 sec it would run again. Turned out the coil in this limit was worn and the system would think it was hotter than it was. Replaced and fixed issue . Only realized I had this issue after installing a WiFi nest thermostat.

the jumper helps let the magic smoke out of the 24v system - that smoke, all bottled up in there somehow.

Very good commentary, could you please show people what they use on today's models.

well explained, thanks

I never knew those came with a pre-hear and I absolutely think I know the application for which it would require one but I only have a sample size of one I had to replace fan limit switch just like that on a 90% furnace I did have to make some adjustments with the fan on and off temperature so the blower would stay running

Thanks, my system uses the yellow wire for the pre heater. I bought a new limiter, but it does not have the connector for this wire, and I couldn't find any videos on what to do in this situation. Thanks.

Thanks

only seen a few with the preheater over the years, seems to me it was mainly on the oldest "high efficiency" units. which nobody around here went for :)

Thank you for the video. Just wanna clarify, based on what you shown. The left side would be 120v hot, and the right is 120v hot to the transformer if there is a jumper. If there's no jumper, then the left side is 120v hot, and the right side is a 24v. And each side has 3 connection points. Correct? Thank you

The fan limit switches that I was told never go bad as long as they get a little lube on them look like a Glass ball with mercury in I seriously hope my carpenter friend never puts 120 on the 24 volt side of a furnace ever again

The same limit switch i have melted down 3 times ...the second time we even replaced the blower motor..any ideas please

I have an old gas furnace (from the 70s I believe) that just has a combination gas valve with a non adjustable fan switch attached. The fan seems to take a long time to turn on after the burners are lit and I feel like I'm wasting heat. Is it possible to update to an adjustable fan switch?

Do you power 24V from the W terminal?

So when you say to isolate the two wires that go under the dial, do you mean to leave them disconnected and tape the ends? The furnace will still work this way? Thanks for any help.

Thanks for your awesome vids! So grateful, you already saved my life, but wonder if you can also tell me if I can simply replace my F&L that has no manual button with one that does have that? I just want to obtain ability to very occasionally turn the fan on when pilot is off and without running heat. Mine is Honeywell, jumper pulled off, four wires in the fat holes, no preheater. If I change it out for one with the manual button, is it safe to assume I just use the same four wires and don't need an extra relay? I believe this gas furnace is a 1973 Whirlpool. (Model FXB47-150ER, serial H33721358). I've seen some say you can simply add a standard light switch or a toggle switch between R and G terminals, which would be even better for me (though I think I want to replace the F&L anyway, it functions correctly, but the face is too corroded to read). I didn't try the switch between R and G, though, because I saw some saying you must add a relay to do that, and I don't know how to find the right relay or exactly where it goes in a switch set up like that. In my furnace, the bar of terminals is along side the "fan center" and has two-screws each at G, C, R, W, Y, X. Wiring diagram shows G could have been wired to T-Stat, but I've only got a double wire to R & W, and too tricky a route for me to pull a new wire. Wiring diagram also shows a "spot relay" on that missing G-to-T-Stat wire, though. I'm not clear whether that is already handled inside the relay box of the fan center. I see only one wire on one of the G terminals, and that goes directly into that relay box area. Thanks a million!!

Hey man, some of the guys at work are shown your videos to help with their training. I still watch them from time to time. I’m out of the Shenandoah valley in Virginia. Anyways, I’m somewhat decent with control wiring. If you don’t mind could you look up this model#-bc-44a8-fa-nlc. It is a fan timer control used on an oil furnace. It gives the user the ability to let the fan control both the oil heat and an air conditioner. In my setup, there is no ac. My fan is not cutting on once the burner fires therefore locking it out. Due to not having ac, and the replacement part being around $400 dollars, im wondering if I could wire this style you have in video in place of that control box style?

They removed the old 5 wire. Only make 4 wire. American standard package units are next to impossible to replace because you get back voltage that turns on a.c and also if you use the wrong one Robert shaw vs Honeywell it won't work. Also requires peanut relays to change them out.

Seems as you’re replying, have a buddy’s whose furnace I just swapped, has a newer Honeywell limit switch, the blower motor runs constantly even with thermostat disconnected, any suggestions

I want to run 2 fans from this thermal control. Can i just jump a second wire in? will it take the extra amps/load?

I've replaced mine set temperature settings as you suggested still getting short cycles. Any suggestions where or what to check next ?

Is there an upgrade to the old style limit switch?.

Interesting.... I know this is off topic but could you give your opinion on hvac damper motor adjustment or replacement , problems or any other info

I just want to know how to change it

Thanks for this video! I have questions on gas fireplaces if you can answer them. I’ve been servicing gas fireplaces and finding dang near every the thermopile on opening circuit only generating 130-150mv and close circuit drop down 50-80mv. Most of the pilot assembly’s are 3ways with pilot, spark rod, thermopile and thermocouple. How is the fireplaces still operating on such low mv? Is this normal or does the thermopiles need to be replace. I’ve tested new thermopile right out of the box and only generate 250mv. Please educate me, I’d really appreciate it, and do right for the customers.

I think I've broken my furnace. I did not remove the jumper wire and when I pushed in the knob to manual, something somewhere clicked and now I have no blower. I see now that the one I replaced had the jumper wire broken off. Is there anything I can do?

Hey can you tell me how to properly wire an A19 low temp cut off thermostat so my heat pump doesn't run all winter?

What the replacement for this?

Well how do I get the wires out of the thing?

What is the modern setup, if these aren't used anymore?

so my round dial sticks sometimes. if you bump it after a while it will often kick on because it gets stuck. is there something i can do or does it need to be replaced? any maintenance to it?

Hello, I looked at the video you made in 2013 ... I want to ask you where I can buy a gas valve for this heater ... this is the mo heater model. make ArcoAIR model GDI075A012CIN MODEL L943259605

can this switch be adjustable?

😅😊😊hi , I'm wondering how the bearing functions . Is bronze stationary in bearing it's self and shaft rotates in bronze piece or is bronze tight on shaft and turns in eating . Maybe you can explain it better . Thank you

Mr. Grayfurnaceman, I need some information if your able to help. I have an issue that just started with my furance with the limit switch. My burners come on and after about 3-5 seconds later, I get a bang/pop that comes from limit switch. Could the bi-metal spring have a sticking point right when heat hits it and it starts to turn? Even though it makes the sound, it still works correctly. Thanks for any help you can provide.

cant find any videos that actually show how to do it

Can I wire a switch to make the fan run on manual if needed I gave a psg wood and oil combo ?

not a very helpful video at all. didn't even show any physical wiring of the switch. just pointing and saying how to hook it up doesn't really help anyone who needs help or anyone who is new to doing this kind of stuff.