Bryant propane heater can't possibly be wired reversed (red LED blinks constantly)

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good..
see Fig 12. Note #5 in the lower right corner.
This wire must be connected to furnace sheetmetal for the flamesensor to work.
THe note is for the return wire of the gas valve.
I'm not sure what they mean exaclty, but something there needs to get to furnace sheetmetal ground for the flame senor to work.
Mark
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Looking up videos on troubleshooting a Bryant 373LAV flame sensor, these guys clean it with a brand new five-dollar bill:
https://www.youtube.com/watch?feature=player_detailpage&v=tYwR9qL4lnk#t
0
This looks like a similar furnace to mine, with a similar issue, and this guy does not recommend cleaning the flame sensor:
https://www.youtube.com/watch?feature=player_detailpage&v=iDnkdKsZhc0#t66

After replacing the flame sensor, he shows the whole cycle:
https://www.youtube.com/watch?feature=player_detailpage&v=iDnkdKsZhc0#t
•0
These guys use #0000 fine steel wool to clean the flame sensor:
https://www.youtube.com/watch?feature=player_detailpage&v=R7AKPgBB_R4#t44

https://www.youtube.com/watch?feature=player_detailpage&v=jCqlGfZv8Es#tY

All say not to touch the sensor with fingers, which I didn't know when I first had cleaned it.
But, interestingly, *all* (of those) simply clean or replace the flame sensor without *any* of them testing it for the 5 or 6 uamps of control current. (I'll google separately for videos *testing* the flame sensor circuit but this is already long.)
Normally, I test things before replacing them, but, none of the technicians in the youtube videos I've found bothered to test it before replacing it.
Even so, I might buy a spare flame sensor and igniter, and keep it next to the furnace. Any suggestions as to good suppliers?
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On 12/23/2014 10:14 AM, Danny D. wrote:

I'd mention a couple, but you need to be in the trade to buy there.
- . Christopher A. Young Learn about Jesus www.lds.org .
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Ok,the flame sensor is just a wire. It does not change resistance with hea t. Also the flame sensor has only 1 connection and as you shoild know, a c omplete circuit needs 2. The circuit is completed THROUGH THE FLAME to the metal burner. And the current does not come from the controller. The flame actually generates the current. The controller senses therescense of thos small current. So the flame is a small battery where the neg terminal is t he metal burner and the positive terminal is the probe in the flame. The c urrent is very small and i would not try to measure it unless you have the right kind of meter and know what to do.
Also the flame sensor in NOT like the thermocoouples which have two wires a nd generate current inthe two wires when heated. The flame sensor is diffe rent.
The flowing hot gas from the burner tothe probe creates a small current.
I donT know how important it is for the probe itself to be clean, but the i nsulator that holds the probe needs to be clean or else the small current w illleak directly back to the grounded metal ans not make it to the controll er.
Mark
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Ok, im a little wrong. The flame senor works by rectification. The controller applies a small AC voltage and the flame lets the current flow in one direction only in effect creating a small DC current. The battery analogy is not exactly right. Goggle flame rectification sensor.
Mark
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On Tuesday, December 23, 2014 7:19:34 PM UTC-5, snipped-for-privacy@yahoo.com wrote:

Well, you learn something new all the time. I thought the flame sensor was a thermocouple. But from some googling, I see you're right. I never even knew this phenomenon existed. It apparently works by using the flame itself to conduct a small current. And somehow the AC gets half-waved rectified in the process.
One big difference with testing, would appear to be that the rod type sensor won't generate any voltage from just heating it. It has to have an AC current applied, so the current test would have to be done with it installed, connected to the controller.
Now the advice to clean them makes sense. If it was a thermocouple, whether it had some dirt on it or not should not affect the operation.
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On Wednesday, December 24, 2014 6:58:04 AM UTC-5, trader_4 wrote:

fect creating a small DC current. The battery analogy is not exactly right .

Hi trader. yes I just learned this too, and it is interesting. Apparently the flame sensor circuits have evolved to this. I read that th e original flame sensors were just measuring the DC resistance through the flame, no flame is an open circuit, and a flame completes the circuit but w ith a high resistnace. The problem is that this is not fail safe. If the insulator that hold the flame sensor gets soot, that leakage resistance to ground can look like a flame. So if the insulator is sooty and the flame s hould go out, the controler would see the path through the soot and think t he flame is present. This of course is very dangerous. So they improved t he circuit, instead of just looking for DC resistnace, they found that a fl ame (unlike soot) conducts current in one direction better than the other. So the newer circuits apply an AC voltage, looks like a high impeandace an d pretty high voltage like 90V AC and the circuit senses that there is more current in one direction than the other. This indicates that there is an actual flame and not just leakage from soot.
So I'm guessing now that the 90 or so volts comes from the AC line and the controller circuit can't work right if the AC hot and neutral and ground ar e not connected correctly.
OP, what kind of VOM do you have. Not all can read MICRO amps. You would have to put the meter in series between the flame sensor and the controlle r. Unless you are good at this, I would not try it, you can cause damage.
Instead if you used an ohmeter to test the flame sensor by itself, connecti ng one lead to the flame sensor and the other to chassis ground, ___ IM GUE SSING__ you might see a resistance of 5 MEG Ohms (that is 5,000,000 Ohms not 5 Ohms) when the flame is present and if you reverse the ohm meter lead s the resistance should be a little lower in one direction than the other. And open circuit (infinity ohms) when no flame is present.
So the practical things to check are that all the ground connections are in place, that the AC supply polatity hot vs neutral is correct, that the fla me sensor insulator is not dirty, that the flame sensor probe itself is not very dirty and that the flame sensor probe is properly engulphed in the fl ame whatever that might be.
good luck
Mark
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trader_4 wrote, on Tue, 23 Dec 2014 06:56:45 -0800:

That's a good point in that the *control board* needs to be grounded, as well, especially, since the *only* DC I can find is in the flame sensor circuit.
Right now I'm looking up how to test the handful of microamps that the flame sensor circuit needs.
I'm not sure how it works yet. I suspect the heat lowers the resistance which then increases the current past a trip point, so, if that's the case, I will try to measure that increased current when I figure out how to measure the current.
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On Tuesday, December 23, 2014 10:18:15 AM UTC-5, Danny D. wrote:

AFAIK, it's a thermocouple, similar to what you'd have in a water heater.
You can probably buy a new one for not too much, might be easier than trying to measure what u have.
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trader_4 wrote:

I use O'scope to check flame sensor. If that is the problem, I'd just replace it. If furnace fired and soon after it quits probably sensor did not sense the flame. Isn't there a test point on the board when temporarily grounded it will go thru logic steps of the operation. I believe all Carrier board has it and Bryant is Carrier 2nd tier product. Control board is quite common amongst brands. My cabin Trane furnace has Carrier equivalent board in there. Furnace operation is just a simple one line yes/no logic flow.
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makolber wrote, on Tue, 23 Dec 2014 07:05:32 -0800:

You're the first person to describe *how* the flame sensor works, so, I appreciate that input, as the first step of measuring something is knowing how it works.
I had suspected that the DC current through the flame sensor changes with heat, such that the controller senses that change.
In the same vein, that's the same as saying the resistance changes, such that the voltage drop across the flame sensor and ground changes (which, I think, is your battery analogy).
I guess I could remove the flame sensor and put a bunsen burner on it and measure the resistance change, but, right now I'm looking up for how to test the current at such low microamperes, when my Fluke 75 only has a 300ma scale.
I do have a cheap Radio-Shack emergency open-jaw ammeter in my car trunk, so, I'll dig that up, but, I doubt it's sensitive enough to go down to a microampere.

The flame is grounded? (I don't understand that statement.)
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makolber wrote, on Tue, 23 Dec 2014 07:05:32 -0800:

This guy tests the flame sensor in situ with an ammeter:
https://www.youtube.com/watch?v=OsIkK3AH1p4

The current for a good flame sensor starts at 0ua with no flame, and then, with flame the ammeter reads 4ua.
https://www.youtube.com/watch?feature=player_detailpage&v=OsIkK3AH1p4#t
2
He mentions that a dirty flame sensor will read lower current, so, now I know at least which direction the thing goes.
a. There is no current when the sensor is cold. b. There is low current when the sensor is dirty. c. There is a handful of microamps when it's hot.
This guy removes the flame sensor and checks continuity all along the stainless steel rod, using a technique I have never seen before for a metal (conductive) rod:
https://www.youtube.com/watch?feature=player_detailpage&v
ÖmnKXZLzzs#t
Here they hook up a Fieldpiece HS36 ammeter into the flame sensor in series,
https://www.youtube.com/watch?feature=player_detailpage&v=OcxQRBbZvpg#t65

They had a reading of 0ua when cold, 2ua when dirty, and 3ua when cleaned. The difference between not working and working was only 1ua, so, a bad ground would certainly affect microamps!
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On Tue, 23 Dec 2014 15:23:20 +0000 (UTC), "Danny D."

I don't think you fully understood his battery analogy. It really generates voltage. Google thermocouple. If you put it in a bunsen burner, use your Fluke on its DC voltage range and measure the voltage to see if it is good. (It is also possible you are correct and the device is a variable resistor that changes with heat, but thermocouples are very common in gas heating appliances).
Pat
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APED Appliance Parts on W San Carlos street in San Jose has igniters, flame sensors and control boards for most furnaces. I've been happy with my purchases from them.
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Scott Lurndal wrote, on Tue, 23 Dec 2014 16:49:18 +0000:

Hi Scott,
Thanks for that tip, as they're very close. They're at 2280 Stevens Creek Boulevard, San Jose, CA 95128.
I called them at 408-977-0404, but, maybe they're on vacation as they didn't pick up the phone (9-6M-F, 9-3 Sat) so I will call again later.
I think, no matter what, I'll get a price on the flame sensor and the control board, since they're the two implicated parts at the moment (other than ground itself).
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Tony Hwang wrote, on Tue, 23 Dec 2014 09:09:33 -0700:

I always wanted an oscilloscope; but I don't have one. :(

Wouldn't you know it, but none of the service manuals have the part numbers. I called Bryant and they said that both Bryant and Payne use the same part numbers, but they didn't have a parts list at their 800-428-4326x3 phone number.
They gave me four dealers to call, and all had messages, so, I left a message with all four, hoping they'll get back to me on the part number for the flame sensor and control board.

I agree. The current conditions are classic for when the flame sensor does not sense the flame (based on all that I've learned yesterday).

Yes. But ...
The test is confusing (to me) as to what the correct procedure is. Here's the test, on the bottom of page 10, of this manual: http://dms.hvacpartners.com/docs/1009/Public/00/SP04-62.pdf
Here's what that test "says": "To initiate the component test sequence,shut OFF the room thermostat or disconnect the "R" thermostat lead. Briefly short the TEST terminal to the ’Com 24V’ terminal. Status LED will flash code and then turn ON the inducer motor. The inducer motor will run for the entire component test. The hot surface ignitor, blower motor-heat speed, and blower motor-cool speed will be turned ON for 10-15 seconds each."
It's not clear which "R" needs to be disconnected, as there is are two "R" wires at the thermostat, and one "R" wire at the control board. I disconnected both.
Then I attached an orange wire to the "COM" terminal and briefly touched the "TEST" spade on the control board.
Nothing happened.
I then turned on the power, and nothing happened when I did that. I then turned on the power and held down the door switch, and, this time "something" happened - but the results were confusing.
First the inducer motor went on (as expected), and then the igniter lit brightly (as expected) and then nothing was visibly happening until the inducer went off, about a minute or so thereafter.
OK. I "think" I ran the test. What did it do? I don't know.
What did it tell me? I don't even know what to look for.

I called Bryant who said that Carrier and Payne and Bryant are all owned by the same company, and that Payne & Bryant are parts compatible.
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Danny D. wrote:

If you want to run test just set the 'stat to lowest setting so it won't call for heat or cool interfering with the test. Just with a short piece of wire jumper the TP and ground momentarily the test will start. Regarding sensor only thing could be different would be connector. If you get one with wrong connector cut the leads and use connector from old one. I know same is the case with HSI(hot surface ignitor) Never touch HSI with bare hand, finger oil will shorten it's life, also it is quite brittle. And cover plate removed, don't forget to cheat the interlock switch. If you want to reset every thing just turn the power on/off otherwise it'll take hours B4 it comes out of lock down mode. All my houses I built I used Carrier product so I am quite familiar with it's design. I always keep a spare HSI. I once got caught in one cold winter night with burnt out HSI. I have to light the furnace with BBQ lighter whenever furnace came on all night. Two fire places in the house were not enough to keep warm, LOL! Good luck. NO white Christmas this year. Day time it is above freezing.
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Tony Hwang wrote:

One more thing. If you indeed need board, it could be universal type with wiring adapter harnesses and instruction sheet. Board is quite pricy, I hope you don't need one.
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http://www.bitscope.com/product/BS05/
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Stormin Mormon wrote, on Tue, 23 Dec 2014 14:45:50 -0500:

No problem. I had guessed that you might have been alluding to a situation where a conclusion would be reached without the scientific logic behind that conclusion.
While a *lot* of people just throw parts at a problem, and even more make inferences that have no basis in fact, I "try" to make logical inferences, and I try to test the fact.
I'm not always right, and, in fact, I'm often wrong; but in the end, the item gets fixed, usually by fixing the right part.
In this case, I "may" have to throw parts at the problem, because every test I "can" do on the flame sensor circuit shows a good sensor, yet, clearly, the flame sensing circuit is not working.
I contacted at least 5 distributors today, and only two would sell a consumer parts. One had the flame sensor for $20, the other for $18, but the $20 lady called first, so I ordered over the phone. Since she didn't require an up-front payment, I presume she has ordered it by now, so, I'll buy it from her anyway.
She had the control board for $450, while the other guy had it for $250, so, that's a bigger difference. I spent a few hours (literally) on my side, in the crawlspace, staring at that darn furnace, reading the three PDFs, staring at that darn thing some more, and, like an idiot, turning it on over and over and over again (even disassembling and reassembling the burners).
In the end, I gave up on debugging further. a) I can't definitively test the flame sensor (I can't even figure out yet how it works) b) It's either the flame sensor or the motherboard, and, c) If it's a ground, I can't find it.
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