trader_4 wrote, on Wed, 24 Dec 2014 04:23:53 -0800:
Too bad I had not seen this wise suggestion, as I did it already, and
it failed to improve anything.
What I did was scratch off as much rust as I could with emery cloth
and a file on the burner itself:
I even used Naval Jelley to remove some of the burner rust:
But, after scraping down to metal, & re-installing ... nothing changed:
I have nominally 90VAC (actually 102VAC) on the flame sensor, but,
0.00ua of current is flowing across the flame to ground:
Stormin Mormon wrote, on Wed, 24 Dec 2014 10:24:11 -0500:
In this case, the flame is spreading from the top burner
(where the igniter is mounted) to the next two burners,
where the burner furthest from the igniter (which is the
bottom burner) has the flame sensor.
They designed the system that way, according to what I read,
because the burner furthest from the igniter is the burner
most likely not to light, if there is a propagation issue.
In my case, all three burners light just fine. In fact, I
am clueless how the flame moves from the top burner to the
next two burners. I guess the flame leaps down from the top
burner to the middle burner due to the unburned propane gas
initially dissipating? And then the same thing, I guess,
happens to make the flame move to the bottom burner where the
flame sensor is mounted.
In this picture below, the left flame sensor is the bottom
one that I cleaned of rust, down to the bare metal.
It didn't make any difference.
Some thing called a flame spreader, which
metal channel goes from burner to burner. Been
a while since I had one of them apart.
At the risk of sounding like a grinch, I'm so
completely tired of that ## furnace. Of course,
I've been sick for a couple days, and not my
usual cheerful self.
Christopher A. Young
Learn about Jesus
makolber wrote, on Wed, 24 Dec 2014 06:03:12 -0800:
I have a Fluke 75, which can only get to around 1ma:
However, I borrowed an Alpha 2360, which can read to 1/10ua.
When I tested the AC voltage, I put a lead on ground and another
lead on the white wire from the control board to the flame sensor.
To test the DC current, I put one lead in the white wire from the
control board & the other lead on the flame sensor spade connector.
In that picture above, you can also see that I've added a black
jumper so that I could short the flame sensor to ground, in the
middle of the 7-second flame.
All I can say is:
a. The sensing of the flame failed.
b. The flame sensor is getting its nominal 90VAC from the control board.
c. There is no current whatsoever when measured in series with the flame
sensor using a meter capable of measuring 1/10ua.
On Thursday, December 25, 2014 1:27:06 AM UTC-5, Danny D. wrote:
Disregard my previous question about the black jumper wire.
I presume you measured continuity from the end of the sensor wire to
IDK how much you can see, but can you see that the flame sensor is
in the flame, ie that the flame is uniform, OK at the sensor?
Did you try testing the meter with some other small current load, to
make sure it doesn't have a blown fuse, etc?
The only thing I can add from all this is that given that you're measuring
normal voltage from the board to the sensor, then the possibility of a
bad ground would seem to be eliminated.
About the only thing left would be that we don't understand the
failure mechanism with the flame sensors. The few descriptions I read,
the physics were not well described. I wonder if it's possible something
changes on the surface of the metal over time, heating, etc that
causes it to stop working? I guess we'll find out when the new one
shows up. But given all that you've found so far, my vote would still
be the sensor. You apparently have 100V on it, no current flowing.
Regarding the current, I know it's supposed to be a few uA. But
I wonder how they define that? Peak? RMS? If it's peak, then it's
going to be substantially less RMS, because remember the flame rectifies
it, so you only have a half-wave, so you have two adjustments to get to
RMS. One that it's a sinewave, the other that it's only half of a sine
I assume when you measure the AC voltage the meter is in the AC volts mode.
And the meter is in the DC current mode when you try to measure the small DC current?
And the leads are plugged into the meter correctly?
On some meters you have to plug the leads into different jack for current measurments.
Stormin Mormon wrote, on Wed, 24 Dec 2014 17:49:41 -0500:
I didn't remove the igniter, but it looks intact in my pictures:
Besides, the igniter is definitely starting the first flame,
which is starting the second flame, which is starting the third
The problem is that this third flame is going out because a flame
is not being sensed. It's a false error.
There's actually nothing wrong with the furnace, except that the
flame isn't being sensed properly.
Typical Carrier part number.
There is only one high Wattage resistor, about middle center of the
board. I have old spare board kicking around here at home or out at
Cabin. I'll dig it out and take a look. If it is not here, I am going
out to cabin tomorrow.
trader_4 wrote, on Thu, 25 Dec 2014 03:32:44 -0800:
I haven't seen that question about the black jumper wire yet, but, I
used it for two different purposes at two different times:
1. To ensure a ground from the burner metal to a chassis ground bolt
2. To short out the flame sensor in the middle of a flame to test it
that would kill the flame immediately.
(Neither effort changed anything.)
You know, I did *not* check that, and I should have, although it sure
looks nice and tight and clean. But, I will check that, although, in
effect, when I checked for the 90VAC voltage, that tested the wire.
I can't see much with the burners in place, but with the burner
removed, the flame sensor is "in" the middle of the flame:
This is a great idea, because the meter isn't mine, so I just
assumed it worked. The meter read 104VAC when I tested the flame
sensor wire to ground, but, that was with the leads in different
holes, and that would be different fuses.
So, it could be that the meter is blown, so, I will try to rig
up a micro-amp test of some sort. (I'd hate to open it up because
it's not mine, although if the fuse is blown, I'd replace it as
a courtesy to my friend).
Do you think so?
But, didn't I make my own ground because I tested that AC voltage at
the white wire from the control board to the chassis ground?
So, if there was a bad ground back to the control board, didn't
I actually circumvent it with the second test lead?
I'm still confused how to test the control-board ground.
Other than cleaning it, which I've done now with emery cloth,
I also can't imagine the thing ever failing. It's just too simple
and sturdy. So, while I am hopeful that the new sensor will solve
the problem, I don't really think it will.
All the videos I watched had no current with no flame and then
it went up to 4 or 5 ua in the flame, but none said how it was
I don't think the Alfa 2360 meter has a choice though, of average,
peak, or root-mean-square. It just has a 400ua scale:
trader_4 wrote, on Thu, 25 Dec 2014 03:11:27 -0800:
I used the black jumper for various purposes in the tests.
1. I used it to "double" the ground from the burner metal plate to
a chassis bolt at a green ground wire at the top of the chassis.
2. I used it to "short" the flame sensor to ground (with the nominally
90VAC white AC wire still connected to the flame sensor) to see if
that shut down the flames prematurely (which it should do in a
Neither attempt changed anything.
trader_4 wrote, on Thu, 25 Dec 2014 03:02:22 -0800:
I can't wait until the grandkids arrive to open their presents!
They'll just have to be a bit bundled up, when they do!
Your suggestion on the non-conductive propane brought a smile to
Sorry to hear about the heater still not working.
That's no fun to be cold, indoors. I've done that
You'd already know that a calorie (food measure) is
actually a measure of heat. So, please feed the kids
lots of high calorie foods to help keep them warm.
Christopher A. Young
Learn about Jesus
Stormin Mormon wrote, on Thu, 25 Dec 2014 08:17:29 -0500:
MERRY CHRISTMAS Chris!
That flame sensor circuit mechanism is the strangest thing to
come out of this quest!
I found this circuit diagram of the flame sensing circuit of a
European Patent number 82106572.9
It's too deep for me though, to figure out yet (plus I have no way of
knowing if mine uses a similar circuit).
I've worked on a dozen or so furnace over the
years. I've had to replace one or two flame
sensors, it's a relatively common part to need
to replace. I hope that works for you. When
yours comes in from the parts place. I do hope
you will let us all know how it works out?
BTW, a long reach nut driver with a magnet in
the socket, is your best friend at moments like
Christopher A. Young
Learn about Jesus
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