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Flue Limit Switch removal safe?

12K views 22 replies 10 participants last post by  plummerdesign 
#1 · (Edited)
I won't go into the saga of how I've arrived at having to ask this question (see QUESTION below to cut to the chase because yes, I have gone into a bit of the saga), but an HVAC service guy who is probably excellent for 99% of his calls had a rough day installing a new Gas Valve on my old furnace. What I think is called a "flue limit switch" had additionally fried, related-to or coincidental-to the gas valve's pilot valve sticking open sometimes, which was the initial problem.

The flue limit switch (shown as maybe OPT on the schematic?) was a smallish plastic thing that once fried, really put out an intense chemical odor (like melting plastic). It sat above all the burner stuff mounted to the round blower housing in its own little sheet metal box, and from what the tech explained, what it does is makes sure there isn't too much heat, and shuts off the burners if there is.

Well, he was going to order its replacement, but in the meantime connected the wires, bypassing the switch, so he could complete the furnace work at hand and get it functioning. Unfortunately he connected the wires exactly wrong, so for hours he was convinced that once the pilot was lit, the sensor was not "rectifying flame", and that's why it would all shut down.

I kept trying to point out that the shutdown was happening way fast (like right away after the pilot lit) compared to how long it previously would seem to "try" to rectify that there was flame before turning the burners on. Finally I guess I said it the right way, pointing out that it was as if that flame check is happening and then some further check is not passing its test, and I pointed up at the jumped wires for that fried/removed piece.

Okay, sorry to have told so much of the saga, but early on he had said that he, as a licensed HVAC guy, couldn't connect those wires to bypass that safety switch, so we basically had a "wink wink" agreement that I connected the wires to bypass the flue limit switch (if that is what it's called). Anyway, when he switched them after my suggestion and considering the schematic again, all worked fine and the plan was that he'd get the part and right after the holidays come back to install it.

Bottom line now is that the part isn't available, and they (local company he works for) sent their invoice (I called several times in January saying there's supposedly a part still on order, and pointing out that I hadn't paid them a dime yet), and on the invoice it reports "system operating safely" and "replacement optional switch is no longer available".

QUESTION: How does this sound to the experienced HVAC people here? Do you recognize that function/positioning of such a switch? ("Flue limit switch" is just the phrase I found online, but seems to be it.) If you do know this backup safety switch, is it something that experienced people would say can be removed and the furnace is still safe?

Or should I not trust the local company saying it's safe and pursue maybe a generic replacement (since the exact isn't available)?

The end of the saga for the service call, of course, is that even a good tech who has a bad day gets pretty expensive, and in his flailing I did also get to buy an ignition control I'm convinced was never a problem. (A universal one from his truck didn't get it to work, and then when he went to the parts store and that ignition control didn't get it all to work either, with all still behaving exactly as my ignition control - which had always lit the pilot - had been. I know the parts store, and there are no returns. Again, switching the jumped wires bypassing the flue limit switch is what got it all working.)

Any insights appreciated, but I won't be able to supply a photograph of the fried and smelly little part 'cuz the tech took it with him...

Thanks,

Rich
 
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#4 ·
The flue sensor is there for a reason. Its a safety device. NO NOT RUN THE SYSTEM WITH THIS DEVICE DEFEATED. You are asking for trouble. the switch burned out for a reason. THE FLUE GOT TOO HOT!!! you are putting the house and people in the house at risk. The professional who bypassed this should not have done so. contact the company and report this and request that it be fixed asap.

They may not have the exact part, but it is critical that any replacement parts have the same operating charitaristics. (ie must open at the exact same temp, same voltage rating etc).

I would contact a second company for an opinion and availablity of the part.

Please be careful!!!!
 
#5 ·
If it was mounted on a housing like that in the pic you posted. Its not a flue sensor. Its an aux high limit. it may have been a combo limit and fan switch. Any York dealer should be able to get it for you.

PS: Thats a 1, not an I
 
#21 · (Edited)
It is a timed on relay/sequencer to keep the fan running a bit longer and start it quicker as you have a reverse flow/counter flow furnace where the air goes down instead of up. the heat rises quickly up when the burner starts and they want the fan to start on a timer as well as the bi metal fan control.

Pictures are worth a thousand words and I could not solve it w/o that pic of the fan with the filters above it.
 
#3 · (Edited)
beenthere,

The furnace is a York PIECD12N04901, and it is over 20 years old.

I can take a photo later, but the switch that's now gone was in a small (3X4 2 inch deep?) sheet metal box mounted on the housing, which looks like this (photo just from internet):



...and if it was mounted on this image, it would be on the slightly curved surface just up to the right of the American flag decal. Four heavy wires go into the sheet metal housing where the switch was, two red and two black.

Like I said, I don't have the switch at all 'cuz the tech took it with him, but I think mine must have had four terminals, but the only switches I could find images of on-line show only two terminals. I include the following image of a switch just to show the solid plastic nature of it. The following image just from the internet has a red reset button, and I can't say for sure if the one removed from my furnace had that or not...

NOTE - THE FOLLOWING PHOTO IS LIKELY NOT OF THE PART I NEED, BUT THE DARK CHOCOLATE PLASTIC ASPECT OF IT IS WHAT I REMEMBER.


Again, I can get a photo of the fan housing, sheet metal box, and the wires running into the sheet metal box later if it would be helpful. Inside the sheet metal box now are just the wires connected (jumpered) and covered with black electrical tape.

Thanks
 
#6 ·
beenthere,

So the York numbers as in "P1E..." (perhaps I had "pie" on my mind when I'd copied it down)

Thanks for the advice and what you say about it being the combo makes a lot of sense. (number of wires and the fact that when it melted down the blower went on/stayed on and the horrendous melted plastic smell filled the house, which at first I thought was gas. That was when I shut the whole thing down and called the HVAC people.)

I'm going to get all the info I can from the company that did the work, and then see what specs I can get from York directly. If the part isn't made anymore, as the HVAC company said, I'll hope they (York) have a replacement with the same specs or a recommendation.

Thanks!

Rich
 
#7 ·
The old part will usually have the limit temp stamped on it. Aux limits are there to stop the fan compartment from getting too hot and come in many different temps.. (Dirty air filters, squirrel cages or a/c coils, faulty motors or fan controls are common causes).
4 wires connected to it is different as is having plastic melt in a fan compartment. I've never seen a fan/limit OEM installed inside a fan compartment but it might explain the 4 wires.
Do you know where those 4 wires run back to?
 
#10 ·
Hmmm, how,

Sorry - I will have to take a photo of the small sheet metal box mounted within my furnace, but I think on the outside of the fan housing. I'd just grabbed the photo in this thread from the internet to show a fan housing 'cuz that's what I pictured. I'll do the actual photo later tonight, but I guess I was thinking the "fan compartment" is the curved sheet metal within which the actual fan spins...

Thanks, and sorry to maybe confuse with the photo shown!
 
#11 ·
Perhaps what the removed switch actually is can better be deduced from where the wires that came from it go.

The following photo shows what I was calling the "fan housing" and the small sheet metal box attached to it (in which the switch lived, but now inside are just the wires and black electrician's tape connecting them to each other to bypass the switch).



The red wires from the empty box (had been from the switch) both go into what I think might be a Fan Relay Transformer (has Rheem 47-19807-01 for the main unit), and in the following photo it is in the metal box to the far left with the wires going in the top and other stuff hanging on it to the right. Red wires look to come from there to what might be the "fan limit switch" (beneath the bottom of the round blower assembly).



The black wires go to the gas valve (one to the M-Main and one to the C-Common, zero to the P-Pilot), and the gas valve is pretty obvious in the above photo.

If this cinches it for what the thing I'm looking to replace actually is, that could help with my contacting York, etc. I will still try to find out the specifics printed on it, but that assumes the tech didn't throw it away, the "limit temp" is still readable on it, and the HVAC company can/will give me some more information.

My gut has told me from the beginning that just 'cuz the furnace works without this switch does not mean it's safe, and the one thing I haven't heard as an answer to my question here in this excellent forum is, "Oh yeah, I'm a HVAC guy and you really don't need that switch." So far I've heard the opposite, and yes, I am going to get it handled. More info from anyone who knows would be good. At this point it sounds mostly like that what I've got there (or more accurately - am missing there) is a combo "aux high limit" and "fan switch".

Thanks for any further info,

Rich
 
#13 ·
An update to this is that with my check to pay the invoice of the HVAC company that did the work and is saying it is safe to not replace the part, I did request any info they had (or the fried part itself if the tech hadn't tossed it) so I could find a replacement or a comparable part.

They sent a pdf of the York parts list for my furnace (doesn't seem to list the part) and a request that I take a picture of the schematic and send that back. Near the top center of this schematic is the part that was removed and hard wired, just down to the right from the hand-circled "ALC" (Auxiliary Limit Control). The part shows "OPT" and has the two red wires/two black wires... The Component Code in the lower left shows that as "Optional Component", and it clearly does stuff based on temperature rising.



The HVAC company is going to ask York directly what that "Optional Component" does and why it would have been in the system, so perhaps it is still possible that it is "optional" and not a safety issue to have had it removed? Seems odd, but we shall see...
 
#15 ·
I know this is an old thread, and while I'd like to include a "conclusion", it's still in the works. I'm communicating directly with York after getting photos of the missing part and a likely part number off of it (I say "likely" 'cuz it was a neighbor's identical furnace for both the photos and the numbers, and while he was kind enough to let me remove the housing from the fan compartment, removing the part from the housing to get an even better photo or a "for sure" read of the numbers felt like asking too much).

York (Johnson Controls in Oklahoma) did request the Serial Number so I was back in looking at the data plate inside the furnace, and it turned out that where beenthere had suggested the "I" in the first three characters of "PIE..." was actually a "1" - well, not so much. It is an capitalized "I" for sure. (An I for an I?)

Stay tuned and I'll eventually get to the bottom of it all and find if anyone's peanuts need to end up in a vise. In the meantime, gladly we've got plenty warm weather here on the west coast...

Uh, photo of the same part on a different furnace is a bit blurry, and the guess at the numbers printed on it was "24V *60704A0-*33, *H26-*85-*C55-*105, *87V".

Thanks,

Rich

 
#16 ·
What evidence is present as it's missing is this is a home warranty call, isn't it? Any tech with half a brain will deny you bypassing that safety switch. He was right from the beginning. Now look what you're doing to him, calling him out like this.

I'd of left you without heat.

What you don't understand is that we walk a fine line, that line being understanding your need for operation and what we can and will do about it. It's the inevitable backstabbing of home owners which is why we should leave you without heat and then once we find out the part is available but not on our immediate need which leaves us transparent, for you to do with us as you please.

If it were me, and I'm sure after this dysfunction with you, he'd as well know better than to trust a customer.

He should not have ever winked at you, he put himself on the line for your benefit. And when your benefit didn't work out as you saw fit you complained. That's what we get for feeling for you.
 
#18 ·
Doc Holliday,

Sorry to get you waving your pistols, but you may have misunderstood. I did make the "peanuts in a vise" comment because the last poster before my update had used that term for getting the service person or company in trouble. But even if the missing part is considered an integral safety device that should be there (which I honestly don't know yet), I would not be doing anything other than eventually letting the tech and his HVAC company know as a friendly FYI what the part turned out to be and how I replaced the functionality.

I promptly paid my bill, I did not complain to them in the least, and the little bit of follow-up to enlist their help to enable me to find out for myself what the part was, what it did, and if I can replace the functionality, has been completely congenial. (The tech took the fried part, had taken a photo of it, and had written down the numbers that were still readable on it, but unfortunately they weren't able to supply any of that info -- no doubt 'cuz, duh, the fried part was thrown away, the photo deleted, and the paper with the numbers recycled. And I'm sure all that happened only because the part was found to be not available, and they'd figured it wasn't necessary.)

The tech was a good guy and I wouldn't hurt somebody in that way (trying to get them in trouble with some bureaucratic monster). If somebody knew I'd used his/their services and asked for a recommendation, I would say that the guy is probably very very good 99% of the time, but on that particular day doing service for me he had a bad day. If they asked for more of an explanation, I'd fill them in on how it proceeded that first off he was at the disadvantage of working on an old furnace (it wasn't a warranty call, by the way), and due to him connecting some wires wrong from the outset, a 45 minute job turned into all day and an unneeded new "ignitor". And it did turn out that the point I was trying to make to him from the beginning (that the problem wasn't that it wasn't rectifying flame for the pilot light) did turn out to be correct. It would rectify pilot flame right away, and then the check of the electric piece which was bypassed incorrectly in terms of which wires were connected, was shutting it all down.

So the most "backstabbing" I'd do (in terms of saying something to a third party who knows who it is I'm referring to) is to present the truth of what happened in this one case, but that my sense is that the tech is a sharp guy who knows his stuff and usually does good work. Everybody makes a mistake at some point.

If I sound like I'm backstabbing the tech in this post (from which nobody would have a clue who he is or who he works for) it may be because so many comments by others here have focussed on it being wrong, and some sort of license-revoking thing, to bypass a required safety switch. But seriously, I wouldn't do anything to him or his company even if that turns out to be the case. And it is still unknown if that is the case.

I totally hope that the electronic part really is "optional", but via my very congenial follow-up with the HVAC company for assistance to determine that, they have not been able to find out what the part is that's now missing, and based on it being identified as "OPT" on the schematic, they are still of the mind that it is not a necessary safety device. And now I'm just trying to find out for sure.

I appreciated his not leaving me without heat and "caring" - as you say. And had he said, "Okay, I have to disconnect the wires now, and my guess is that part is a last ditch safety device to kick-in in case all others fail and there is a fire going on and the valve has not been shut off yet, so if you want to reconnect them you will have heat," I would have reconnected them. (Some in these forums will no doubt now say it's a miracle I'm alive!) He was supposed to get back to me in a couple weeks, but nobody ever did. He (or they, the HVAC company) should have contacted me and told me the part was not available and by their estimation it's safe to run my furnace. I don't think that's not "caring", but just, uh, not dotting an i or two...

My best to Wyatt Earp...

Rich
 
#19 ·
I believe that the part you have in the picture is a time delay control. TDC on your schematic. Mine burned up also (terrible smell) and the fan runs continuously. 60704a0-33 is the number on mine. I think it heats up when the gas valve comes on then makes contact to the blower. When the gas valve turns off, the heat keeps the TDC on which keeps the blower on until it cools and contact is broken. I could be wrong about that though. the important part is what to replace it with. Has anyone found a replacement that is a direct wire?
 
#20 ·
swren688,
I believe you are correct about it being a "TDC", possibly also called a "sequencer" or "time delay relay". I had no luck finding out what my missing part was or what a replacement part would be going through York, so I took a shot at going to the original old HVAC company that had installed the furnace long long ago. That guy was very helpful, knew what it was (again, "sequencer" was what he said and his explanation of what it did made good sense at the time, though I can't say for sure it was exactly what you describe). And the guy did find a replacement.
I think the replacement is all about functioning at which volts and other hints in the numbers printed on the sequencer, and the replacement he found for me has "H1-20 C40 110 A1250" on it and looks to be this one:
http://www.parts4heating.com/A0341-Time-Delay-Relay-Thermodi-p/2400-062.htm
As far as wiring, I did let them install (overall cost after the entire fiasco not much less than had I bought a new furnace, but... well, it's safe now), and the two red wires attach to the top/inside/silver prongs, and the two black wires to the bottom/outside/brass prongs. This matches someone's advice I find via a search for 60704a0-33, so I don't think it matters which red or black is on which side?)
http://www.justanswer.com/hvac/2sl6l-rheem-downdraft-gas-furnace-the-fan-always-running.html
Hope you get yours working again soon.
 
#22 · (Edited)
So glad to have found this article. What a long path to a solution! Today I found that my time delay relay switch 24v 60704A0-33 has fried too. (same exact York furnace)
A local HVAC tech was here when I opened the junction box and said to "bypass it". This does not set well with me either. This part is made of UNOBTAINIUM it seems.
Richapple, were you able to procure the needed part?
Thanks for this forum.
 
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