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

Page 6 of 11  
Stormin Mormon wrote, on Tue, 23 Dec 2014 14:48:27 -0500:

I called a few today.
My hastily written notes are below, but I may have mixed a bit up as almost all had to call me back so I invariably didn't have my paperwork with me when they called back, so, it was hard keeping them straight since they all sounded the same.
Slakey Brothers 1480 Nicora Avenue, San Jose (sells only to contractors).
Appliance Parts, Bob 408-265-5030, San Jose (sells to humans, $18 flame sensor, $250 control board)
APED Appliance, San Jose 408-977-0404 (sells only to contractors)
Residential Heating and AC 888-818-6374, Campbell (sells to humans, $20 flame sensor, $450 control board)
Air Care Heating & Cooling, San Jose 408-513-3089 (doesn't sell parts, $80 for a service call)
Coldcraft 888-918-8662 (doesn't sell parts, $139 for a service call)
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makolber wrote, on Tue, 23 Dec 2014 16:08:42 -0800:

I don't profess to understand how that flame sensor works, but, it does, perhaps, seem to have *two* connections.
1. The spade where the white wire goes, and,
https://c4.staticflickr.com/8/7516/16091574382_cd0760b5ca_c.jpg
2. Ground (where it's bolted to the chassis).
https://c4.staticflickr.com/8/7480/16066499206_037e94f4f8_c.jpg
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makolber wrote, on Tue, 23 Dec 2014 16:19:30 -0800:

There are only two ways to test a component: a) (Perhaps blindly) following a test procedure, or, b) Understanding how it works and improvising an appropriate test.
I can't blindly follow the stated test procedure because I can't easily measure from 1 to 6 microamperes.
I can't logically improvise a reasonable test procedure because I can't figure out how the thing works.
I did try measuring resistance from spade to tip, which varied: 0.2 ohms
https://c4.staticflickr.com/8/7516/16091574382_cd0760b5ca_c.jpg
0.6 ohms
https://c4.staticflickr.com/8/7523/15472612623_6bf1054855_c.jpg
And I verified that the flame sensor "body" is attached to ground: 0.2 ohms
https://c4.staticflickr.com/8/7480/16066499206_037e94f4f8_c.jpg
I doubled up on the ground from the flame sensor body to the chassis ground, (it's hard to see the black alligator clip wire in the photo below, nor the tape on the door switch, but this is that test):
https://c4.staticflickr.com/8/7534/15906204369_bb93846665_b.jpg
With the flame sensor body ground doubled, I cycled the furnace, just to make sure that a bad flame sensor ground wasn't the problem:
https://c4.staticflickr.com/8/7512/15905008010_5dd60a52f2_c.jpg
In the hopes of doubling the control board ground, I looked (in vain) everywhere I could on the controller board for a named GROUND, but never did fine a single connection called "ground":
https://c4.staticflickr.com/8/7564/16091574612_858288d901_c.jpg
All these tests were in vain.
I still don't know if it's a bad flame sensor or a bad circuit board.
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trader_4 wrote, on Tue, 23 Dec 2014 08:00:29 -0800:

The flame sensor is $20, and it's on order.
At the moment, it could be any one of three things: 1. Bad flame sensor (let's hope), 2. Bad circuit board (let's hope not as the quotes are $250 & $450) 3. Bad circuit board ground (I wish).
I know you suggested I check the ground on the circuit board, but, try as I might, I can't find a single connection "labeled" ground!
https://c4.staticflickr.com/8/7517/15904853178_6d15b36c3e_b.jpg
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On Tuesday, December 23, 2014 11:32:58 PM UTC-5, Danny D. wrote:

Presumably the AC line is connected to the controller. Follow the green wire/s. The incoming ground will be connected to the cabinet frame, typically right where the connection is made. And typically, you'd have a green wire at the controller, together with the hot and neutral, that probably goes back to that incoming connection point too.
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Tony Hwang wrote, on Tue, 23 Dec 2014 13:57:56 -0700:

I don't understand that test.
It "sounds" like a good idea, and it's *easy* to run:
https://c4.staticflickr.com/8/7559/15906205029_b8ed919914_b.jpg
But, whatever it does, doesn't tell me anything. It just runs 'stuff', and that's about it.
I must be missing the magic of this so-called "component test". I *wish* it gave me useful information.
But, I get nothing out of it, and, I'm not even sure that the "component test" tests the flame sensor anyway, since the flames never start up during that so-called "component test".
So, at the moment, I think it's the most over-rated test that has been suggested, to date! :)
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On Tuesday, December 23, 2014 11:36:56 PM UTC-5, Danny D. wrote:

It's not over-rated if the inducer blower, air handler blower, etc has failed.....
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Tony Hwang wrote, on Tue, 23 Dec 2014 13:57:56 -0700:

I taped over the door switch, so that's not a problem.
Thanks for the warning on the brittle igniter.
Here, where I've removed the three burner tubes, you can see that the speckly igniter is only at the top burner, while the rod-shaped flame sensor is only on the bottom burner, with the middle burner being left alone:
https://c4.staticflickr.com/8/7467/15904852758_68609d3825_c.jpg
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Danny D. wrote:

Don't worry about the voltage out of transformer. It does not have tight specs. Can be as high as 32V AC. IIRC, the test runs the logic sequence up to the point of running normally. If some thing is not right it'll tell via error code. Did you see the HSI glowing to ignite? If so definitely next step is sensing flame by sensor, if not it'll quit and go into lock down mode but blower is still running to cool off. Then you have to power down and up to get out of lock down mode. If it has ground problem then clip one meter probe to furnace frame and probe all the [point on the board Ohmming it out to see any unusual high resistance at any point.
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Tony Hwang wrote, on Tue, 23 Dec 2014 14:04:50 -0700:

I was only able to get two quotes for the board, the first being $450 and the second being $250, neither of which was in stock.
I spent at least an hour (or more) on my back, looking the board over, and I don't see a single burn mark or obviously bad component:
https://c1.staticflickr.com/9/8669/15904853568_4203e811cb_b.jpg
I did figure out the terminal sequence though, which you can see I drew a simplified diagram of on the chassis in the picture above. COM === the unswitched neutral out of the 24VAC (nominal) transformer RED === the power to the thermostat (which is switched in the thermostat) WHI === the power coming out of the thermostat to call for heating YEL === the power coming out of the thermostat to call for cooling GRE === the power coming out of the thermostat to call for the fan
The transformer, nominally 24VAC, tested at 28VAC, by the way.
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Scott Lurndal wrote, on Tue, 23 Dec 2014 21:28:09 +0000:

Thanks Scott,
I have a call to a scientist friend, who might have the capability to measure 1 to 5 microamperes of current.
A funny thing is that one of the service personnel told me to measure "5 ohms" (I swear I heard him right) of the flame sensor.
When I questioned him, he said he always measured if it was 5 ohms. When I asked him *how* he measured it, he *clearly* explained that he hooked one lead to the disconnected wire and the other lead to the spade on the flame sensor while the flames were heating it up.
He kept telling me that was ohms, and I told him two or three times that he can't possibly be measuring ohms that way, but he insisted he tested the ohms that way all the time, and determined whether a flame sensor was bad that way.
Sometimes these technicians scare me.
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On Tuesday, December 23, 2014 11:49:39 PM UTC-5, Danny D. wrote:

Maybe he's not as dumb as he sounds. If you put a VOM on the ohms setting, it's providing a voltage source. You now have that connected to the flame sensor. The flame sensor apparently only conducts in one direction, but if you had the polarity right, you would think it would pass some current through the flame, just like under normal operation. That in turn would result in the VOM reading some kind of resistance. But you'd think it would be a lot higher than 5 ohms. And that also assumes he meant you should test it installed, with flame.
Now that we all know how the flame sensor works, I'm left wondering what there is to fail? It's just an electrode. About the only thing that I can see that could fail would be either the attachement wire coming loose or the insulator failing. Both of those should be testable with a VOM, without the need for flame, etc. But maybe something can change in the surface of the metal that reduces it's ability to conduct too.
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Pat wrote, on Tue, 23 Dec 2014 11:01:12 -0500:

I will fully agree with you! I do *not* know how the flame sensor works.
It appears to have two *external* electrical connections. 1. The spade end that has the controller wire connected to it, and, 2. The body (which is bolted down and presumably grounded as a result).
What is not clear are the *internal* connections (if any).
When I tested it cold, there was no connection between the spade end and the body ground:
https://c4.staticflickr.com/8/7470/15469975964_62d3a691fb_b.jpg
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Oren wrote, on Tue, 23 Dec 2014 14:46:23 -0800:

I remember that story, as you've said that before, I forget why, but, probably in reference to an AC part, when I had to fix my sister's AC unit.
If it matters, I took all three burners out, but, there was nothing I could see to do with them once they were out, except snap a photo:
https://c4.staticflickr.com/8/7510/16090369371_7ef06fc142_c.jpg
That did enable me to confirm that the flame sensor, which is on the lower burner in the photo below, was mounted squarely in the flame:
https://c4.staticflickr.com/8/7467/15904852758_68609d3825_c.jpg
Googling for how the flame sensor works, it seems very few people actually know, or, if they do, they are all explaining something different.
How does a flame sensor work and how do you test it: http://heatingandaircooling.com/2012/11/16/how-to-test-flame-sensor/
How does a furnace flame sensor work: http://www.ehow.com/how-does_4924695_furnace-flame-sensor-work.html
How does the gas furnace flame rod work:
https://www.youtube.com/watch?v=uJU3806j2CE

etc. (I'm still reading up on this...)
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makolber wrote, on Tue, 23 Dec 2014 16:08:42 -0800:

I'm trying to make sense out of these four descriptions of how the typical gas furnace flame sensor works (because if I knew how it works, I could devise a test that might not require measuring from 1 to 5 microamperes, which I can't adequately measure with my Fluke 75).
How a flame sensor works: http://thehvacguy.wordpress.com/2012/12/06/dirty-flame-sensor-problem/
How does a flame sensor work and how do you test it: http://heatingandaircooling.com/2012/11/16/how-to-test-flame-sensor/
How does a furnace flame sensor work: http://www.ehow.com/how-does_4924695_furnace-flame-sensor-work.html
How does the gas furnace flame rod work:
https://www.youtube.com/watch?v=uJU3806j2CE

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Danny D. wrote, on Wed, 24 Dec 2014 04:45:28 +0000:

It's not clear, to me, whether that's because of RMS versus average measurements, but the measured 28 VAC is close enough for our purposes to assume the switched power to the RED terminal isn't a problem.
What's harder to understand is the unswitched COM terminal.
It seems to be an unswitched neutral, coming out of a center-tapped transformer, especially since it doesn't seem to go to the thermostat, but, it does go to the AC unit.
Anyway, for some purposes, I assume it's not a center-tapped transformer, and that the COM is simply the unswitched other side of the transformer, where the RED is the switched side of that transformer.
But, for other purposes, I assume the COM is a "neutral" of sorts, coming out of the middle of a 12VAC + 12VAC transformer, which makes it a ground, of sorts.
All this probably just tells you that I don't really understand what exactly the switched RED and unswitched COM terminals are, but, in reality, that's not the problem with this furnace, so, that's just a diversion away from the real problem, which is determining whether the failed part is, either: a) A bad flame sensor ($20 part is on order), or, b) A bad control board ($250 to $450 part can be ordered), or, c) A bad circuit board ground.
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Scott Lurndal wrote, on Tue, 23 Dec 2014 21:28:09 +0000:

I got an idea for a test of the "flame rod" from this video.
https://www.youtube.com/watch?feature=player_detailpage&v=uJU3806j2CE#t
8
The guy shorts out a good flame rod, and the flames stop.
If I short out mine, during the flames, it should also stop the flames quicker, and, if it doens't stop the flames right away, that would be an indication that it's not doing anything.
Of course, either way, I still wouldn't know if the control board is bad, but, it's worth a test to see what happens.
Also, I noticed his autopsy of a flame rod shows that there is apparently *no connection* from the flame rod to the steel body of the flame rod.
https://www.youtube.com/watch?feature=player_detailpage&v=uJU3806j2CE#t
6
So, it *is* a single-wire sensor!
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On Wednesday, December 24, 2014 12:23:26 AM UTC-5, Danny D. wrote:

I didn't watch the video, but I'm guessing that he did that with a furnace that started up and was operating, ie it was past the first few seconds. From what you've said, yours isn't doing that. The sequence is the furnace turns on the gas, ignites. At that point I would think it doesn't care what's going on with the flame sensor. It's only some seconds later, when there should be flame, that I would think the flame sensor would matter. So, past that point, if you shorted it out, then I'd expect it would force a shutdown. But you aren't there, you're in that initial fire up window.

Of course there's no connection from the rod to the metal body. It relies on the flame to make the connection. That's how it works.
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Danny D. wrote:

If you are stuck at this point then new sensor or board, only two choices, right? Being retired from Honeywell I can lean on guys still working there, electricians, process control technicians, etc. When I need parts I get help from them. On the control board there ought to be a chip(maybe op amp) which will convert that small amount of current to normal logic level(5V DC) to feed to ASIC(the brain of board) telling flame is on. One time there was a TSB out regarding one high Wattage resistor over heating causing solder joint to fail intermittent. I used tyo reinforce the solder joints and drill holes on the board cover near the resister for more cooling. If this resistor has poor solder joint, it will produce all kinda funnies.
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Danny D. wrote, on Wed, 24 Dec 2014 05:11:13 +0000:

Now that I've seen the insides of a flame-sense rod, I can't imagine, other than getting dirty, how they can *not* work.
It's just a steel rod inside a ceramic insulator.
Nothing more than that. It's about as simple a construction as can be imagined.
In fact, this guy, who says he's an instructor, says he can't get a flame rod to fail!
https://www.youtube.com/watch?feature=player_detailpage&v=0ZYXK8450mM#t
!7
He says you can clean it with just about anything (even a file):
https://www.youtube.com/watch?feature=player_detailpage&v=0ZYXK8450mM#t90

Tomorrow I'm going to three more aggressive ways to clean it:
https://www.youtube.com/watch?vmsKn1Rw9Yo

But, it's looking less and less like the flame rod went bad. :(
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