Furnace Limit Switch

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Aaron
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Re: Furnace Limit Switch

Post by Aaron » Thu Dec 20, 2018 11:36 pm

I just replaced the fan motor on my Payne in the ass furnace this past summer.


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A. Spruce
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Re: Furnace Limit Switch

Post by A. Spruce » Thu Dec 20, 2018 11:40 pm

Aaron wrote:
Thu Dec 20, 2018 11:29 pm
BTW, I had a Coleman furnace for 25 years. The one I have now was made by a company called Payne. I am really not so sure there is much difference between brands. They all seem to work with commodity parts.
Yes, but did you live in a trailer or a real house? If it was a real house, I guarantee that the furnace was at least 10 times better quality, regardless of the name on the side of it. The trailer industry has gone out of their way to make everything well below the standards set by the stick framed home industry. Oh, they tell you all sorts of lies while they waltz you through their factories, but not a single word out of those lying bastards mouths is true.
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Re: Furnace Limit Switch

Post by Aaron » Fri Dec 21, 2018 12:07 am

I'd say theres not much difference between the furnace you're dealing with and mine. I replaced the aforementioned control board once after 15 years. HVAC company wanted $850 to do it. I bought it on eBay for $60 and did it myself. That's how I learned all the circuitry.

My furnace developed a crack in the heat exchanger at 25 years. That is where you run the risk of CO leakage. So it was time to change it out. My uncle works for a commercial HVAC company and had connections to buy one wholesale. He installed it for me as a favor.

My A/C condenser outside is Coleman. That still works fine. It uses the old R-22 freon.

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Re: Furnace Limit Switch

Post by A. Spruce » Fri Dec 21, 2018 1:00 am

R-22?!?!?!!? Are you CrAzY?!?!?! You're supposed to be using unicorn farts! :mrgreen: (it's ironic that this smilie is called "mrgreen"! :lol:
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Re: Furnace Limit Switch

Post by Shannon » Fri Dec 21, 2018 8:14 am

A. Spruce wrote:
Thu Dec 20, 2018 7:49 pm
When it did not shut off per temp setting, first we lowered stat setting, I pulled it the stat off the connector, it continued to burn. I had to turn off the gas to shut down the system. I left everything alone after that, the fan shut down by itself shortly after the flame was terminated.

In playing with it today, the stat and furnace relay clicked when I upped the stat setting and dropped the stat setting in relation to the ambient temp.
Sounds like your gas valve is sticking open to me now that you posted this info.
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Re: Furnace Limit Switch

Post by Shannon » Fri Dec 21, 2018 8:21 am

LOL,just read through all the posts now and I guess Wayne thought of the gas valve as well.
You guys developed a 3 page thread really quickly yesterday! :lol: :lol: I think it is a new record here?
I hope this is the answer to your problems Spruce, I hate to see you have to pull on a sweater over the holidays. You probably have a closet full of ugly xmas sweaters. I know.. I know they where not called that 20 yrs ago when you bought them but they are now and they are worth a fortune now also !! :o :o :o
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Re: Furnace Limit Switch

Post by emtnut » Fri Dec 21, 2018 12:01 pm

A. Spruce wrote:
Thu Dec 20, 2018 10:20 pm
I will try to fire it in the morning, but I won't have the limit switch, so I don't know if it will go or not. Most that can happen is it goes boom, right? :| :? :shock: :lol: :lol:
I don't think anything was wrong with the old limit switch. Unless there was something else going on ??

I wouldn't try the gas valve until the switch is in. It starts the fan when it gets hot in there.

When you do try, really make sure there is no gas smell anywhere. Have your lighter on the pilot light BEFORE you open up the gas. If it is still stuck open, the furnace will light up right away. Be ready for it ! (nothing wrong with that, just can startle you.)

Pretty sure this is your valve .... https://hvacpartstore.myshopify.com/col ... -gas-valve
Can you confirm that yours only has the 2 wires to it for me ?

In case you want some bedtime reading, here's the manual :lol:
https://cdn.shopify.com/s/files/1/1071/ ... 3615234981
(it includes a few different models, but yours is covered as well)
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Re: Furnace Limit Switch

Post by emtnut » Fri Dec 21, 2018 12:07 pm

Shannon wrote:
Fri Dec 21, 2018 8:21 am
LOL,just read through all the posts now and I guess Wayne thought of the gas valve as well.
You guys developed a 3 page thread really quickly yesterday! :lol: :lol: I think it is a new record here?
I hope this is the answer to your problems Spruce, I hate to see you have to pull on a sweater over the holidays. You probably have a closet full of ugly xmas sweaters. I know.. I know they where not called that 20 yrs ago when you bought them but they are now and they are worth a fortune now also !! :o :o :o
Great minds .... :lol:

Poor Sprucy, might have needed that Christmas sweater AND a blankie last night !
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Re: Furnace Limit Switch

Post by A. Spruce » Fri Dec 21, 2018 1:21 pm

emtnut wrote:
Fri Dec 21, 2018 12:07 pm

Poor Sprucy, might have needed that Christmas sweater AND a blankie last night !
Hey now, you can give me poo about the sweaters all you want, but don't you dare bring Binkie into this! :evil: :lol: :lol:

Back on topic, I'm pretty sure the limit switch is bad, it tests "open", which it shouldn't, and the fan cycles a lot, which according to YT vids is an indication of it being bad. I don't know how to test the fan relay, but I'd guess that's possibly a culprit for the cycling as well. When the unit cycles, it is the fan turning off and on every few minutes, the burner stays lit. This is the problem it's always had.

A few years ago, one tech diagnosed the pump as being bad, by "pump" I'm assuming it's what you guys are referring to as the valve, whatever the case, it's the silver control dohicky that the incoming gas flows through that has the pilot lighting switch on it. The tech that replaced the section of ducting tested this device and didn't find it out of spec, maybe a little low, but well within functional range.
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Re: Furnace Limit Switch

Post by A. Spruce » Fri Dec 21, 2018 1:28 pm

emtnut wrote:
Fri Dec 21, 2018 12:01 pm
I wouldn't try the gas valve until the switch is in. It starts the fan when it gets hot in there.
I'll just put some duct tape over the hole in the fire box, that should be fine, right? ;) ;) Roommate will have the switch with her tonight when she gets home from work, I'll wait until then. 8-)

That does look like the manual, the roommate took our with her to the parts store.

The gas valve does indeed have only two wires.
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Re: Furnace Limit Switch

Post by A. Spruce » Fri Dec 21, 2018 1:29 pm

Shannon wrote:
Fri Dec 21, 2018 8:21 am
LOL,just read through all the posts now and I guess Wayne thought of the gas valve as well.
You guys developed a 3 page thread really quickly yesterday! :lol: :lol: I think it is a new record here?
We were 3 pages in before Aaron realized that there was no control board. :lol: ;) :mrgreen:
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Re: Furnace Limit Switch

Post by A. Spruce » Sat Dec 22, 2018 12:03 am

Well, roommate came back empty handed. Said supply house tested the limit switch and said it was fine. Correct me if I'm wrong, but there are only two readings, continuity "0" and no continuity "infinite", the switch reads infinite with my ohm meter. With the switch cold, it should be closed, allowing the fan to operate, thus it should have continuity.

I also told her to get a price on the gas valve, the supply house hautily told her to F-off, they don't diagnose problems and they'd have to order the part from Coleman anyway, so F-off, we're not interested in helping you or selling anything to you. I've had similar issues with this supply house, though being male and a contractor, they tend to give me a little more leeway. Unfortunately, they're about the only game in town for parts.

I will be reassembling the furnace tomorrow and see what happens. I'm hoping that the burner is still stuck in the on position and that tapping on the gas valve will shut it down as it's supposed to, if so, I'll order a new valve and put it in myself. As for the electrical diagnosis, I'll probably leave that to a tech and watch over his shoulder to see what he's monkeying with and what the fix is for the issues currently presenting themselves.
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Re: Furnace Limit Switch

Post by Shannon » Sat Dec 22, 2018 8:09 am

Are the two switches the same? If so could you swap them and test that way?
Also it sounds like Amazon may be the way to go for your parts? I know a great link you could use! ;) :)
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Re: Furnace Limit Switch

Post by Shannon » Sat Dec 22, 2018 8:28 am

pretty sure this is your valve on Amazon?https://www.amazon.com/LTD-Standing-795 ... e+7956+336

Yes this is the valve i found your old number on the parts sheet and it cross references to this one .
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Re: Furnace Limit Switch

Post by emtnut » Sat Dec 22, 2018 9:33 am

A. Spruce wrote:
Sat Dec 22, 2018 12:03 am
Correct me if I'm wrong, but there are only two readings, continuity "0" and no continuity "infinite", the switch reads infinite with my ohm meter. With the switch cold, it should be closed, allowing the fan to operate, thus it should have continuity.
Nope. When cold, the switch should be 'no continuity- infinite resistance'

When the temp reaches 110˚F, the contact closes and starts the fan. That would be 'continuity-0 Ohms

On shut down (when the flames stop) the fan will run until it reaches 90˚F

The 20˚F difference you wouldn't be able to check (well, without a lot of test equip)
Change it and see what happens.

I think what is happening is either these are cheap switches, and don't keep that 20˚ difference , or the airflow in the furnace is somewhat restricted somewhere.
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Re: Furnace Limit Switch

Post by A. Spruce » Sat Dec 22, 2018 11:42 am

This furnace has basically no filters. It started life with a very lightweight foam filter and currently uses the super cheap fiber mesh filter. There's no easy way to see inside the system to know if air passages within the heating exchange chamber have plugged or diminished.
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Re: Furnace Limit Switch

Post by Aaron » Sat Dec 22, 2018 1:23 pm

I use those cheap mesh filters too.

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Re: Furnace Limit Switch

Post by A. Spruce » Sat Dec 22, 2018 2:14 pm

I pulled the fan, unfortunately, it only allows viewing of the top of the fire box, the AC condenser is under the fire box and not easily accessible. If there is an air flow blockage, it would be the AC condenser. Having said that, we have floor registers, so they are constantly being stepped on, with that, I have not noticed any lack of air blowing out of the registers.

I reinstalled the limit switch and tried to light the pilot, no joy. This has never been an easy furnace to light, mostly because there is no definitive pilot location to stick the match. After several attempts, I'm calling a tech and hope they can come early next week, even though Xmas is Tuesday.

I'm guessing that it's a combination of things, like I said, this furnace has had recurrent issues and it's always been the same switches and relays that go bad. This time it's probably the gas valve too. We'll see what the tech says.
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Re: Furnace Limit Switch

Post by Aaron » Sat Dec 22, 2018 3:37 pm

Drat. Hope they can narrow down the problem for you. 😕

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Re: Furnace Limit Switch

Post by A. Spruce » Sat Dec 22, 2018 3:44 pm

Something just popped out at me, does the fan relay need to be solidly bolted to the chassis for grounding purposes? As I am putting things back together, I realized that the relay wasn't well secured before and not at all when I tried to light the pilot. Hard to believe this would keep a pilot from lighting, but stranger things, right?
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Re: Furnace Limit Switch

Post by A. Spruce » Sat Dec 22, 2018 4:11 pm

Nope, still no joy.
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Re: Furnace Limit Switch

Post by emtnut » Sat Dec 22, 2018 5:08 pm

A. Spruce wrote:
Sat Dec 22, 2018 3:44 pm
Something just popped out at me, does the fan relay need to be solidly bolted to the chassis for grounding purposes? As I am putting things back together, I realized that the relay wasn't well secured before and not at all when I tried to light the pilot. Hard to believe this would keep a pilot from lighting, but stranger things, right?
No, the fan relay has 2 wires on screw terminals for the 24v and ground connection.

If the pilot won't light (or you can't get a match in there to light it), then the flames won't start, and the furnace will do nothing.
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Re: Furnace Limit Switch

Post by A. Spruce » Sat Dec 22, 2018 7:18 pm

It has always been a pain finding exactly where to put the match to light the pilot, however, in this particular instance, no amount of match waiving is working. I've got a call into a tech to come take a look, we'll see when they get back to me, considering this is a Saturday and Christmas is on Tuesday. Thankfully, our day temps are 55*F and nights are 44*+ until Tuesday, when they drop to 38* and less through the week.

As always, thank you Aaron and Emtnut for all your help, it's been very appreciated. I'll update as I have new info to provide. 8-)
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Re: Furnace Limit Switch

Post by Aaron » Sun Dec 23, 2018 12:25 am

You have an electric heater or two just in case?

Hope it's a simple fix that can get done before xmas.

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Re: Furnace Limit Switch

Post by A. Spruce » Sun Dec 23, 2018 12:38 am

Nope, no backup heat, we'll just have to bundle up if it gets too chilly.
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Re: Furnace Limit Switch

Post by Aaron » Sun Dec 23, 2018 12:56 am

I have a small 1500 watt radiator on wheels. Sometimes I use that when I want heat but don't feel like heating the whole house.

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Re: Furnace Limit Switch

Post by Shannon » Sun Dec 23, 2018 7:52 am

I hope you can get this fixed up. Did you try reaching your pilot with one of those plastic lighters that reach in a ways. Will be easier then a match. The furnace should not be that hard to light. When lighting can you hear the gas when you are trying to light?
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Re: Furnace Limit Switch

Post by A. Spruce » Sun Dec 23, 2018 11:46 am

Shannon wrote:
Sun Dec 23, 2018 7:52 am
I hope you can get this fixed up. Did you try reaching your pilot with one of those plastic lighters that reach in a ways. Will be easier then a match. The furnace should not be that hard to light. When lighting can you hear the gas when you are trying to light?
No the pilot is to far in for that, it takes long matches and a wire match holder to reach it. Just heard back from the HVAC tech, he suspects gas valve too. Will be seeing him Monday morning, but due to Xmas, may not be able to get parts until Wednesday. He seems well versed in Coleman trailer furnaces! :lol:
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Re: Furnace Limit Switch

Post by Aaron » Sun Dec 23, 2018 1:15 pm

Well Spruce sounds like you may have a Charles Dickens xmas.

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Re: Furnace Limit Switch

Post by A. Spruce » Sun Dec 23, 2018 1:25 pm

That gives me an idea, I could fire up the BBQ in the middle of the living room! :P
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