Testing a Carrier Pilot Electrode Wire


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Old 11-03-11, 08:17 PM
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Testing a Carrier Pilot Electrode Wire

What should the maximum resistance in ohms be for a Carrier Pilot Electrode Wire (connecting the igniter/lockout control board to the 3-wire pilot spark ignitor)?

Furnace model: 394JAZ036065AAFA
Igniter/lockout control board model: LH33WZ512A
3-wire pilot model: 740A
Spark ignitor model: LH680512
 
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Old 11-03-11, 10:37 PM
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I can't imagine what you are trying to test.


My suggestion would be to describe any problem you are having with your equipment. The Carrier 3-wire pilot is a widely understood system on this board and I would suppose you can get some help figuring out a problem.
 
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Old 11-04-11, 08:26 PM
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Try removing the wire from the spark module, now with the tstat calling for heat take a insulated handle screwdriver and touch the center post on the spark generator. Now draw the screwdriver away to about a 1/4 in and see how strong the spark is, should jump between the two strongly. I'm assuming you have no spark??
 
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Old 11-05-11, 09:34 AM
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I do have spark, but it often fails to ignite the pilot, so I suspect that the spark is not strong enough. I measure the electrode wire resistance at 0.5 ohms, but I don't know what the specified limits are for that wire.
 
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Old 11-05-11, 12:29 PM
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I don't know the specs, try and cut a 1/4 " off each end if you have enough wire. Or just replace the wire, however in my years I don't think I ever saw one fail anywhere but an end. Most of the time when the pilot fails to light it is due to a dirty pilot
 
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Old 11-05-11, 04:45 PM
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Don't even bother with the wire --- it's not the issue.

You have one of two problems:

1) a dirty pilot burner and pilot orifice which need to be cleaned or

2) a bad ignition module that isn't providing a hot enough spark to light the pilot reliably.


It's FAR more likely that the pilot burner needs to be cleaned, and cleaning it is probably maintenance that has been neglected in any case.

So disassemble the pilot burner and the brass nut that holds the pilot orifice in at the end of the pilot tubing. Clean the pilot orifice with the wire from a wire brush and the rest of the pilot burner with a wire brush.

Reassemble and report what happens.

The pilot burner and orifice should be cleaned annually to get reliable service from this part.
 
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Old 11-06-11, 09:35 AM
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Actually, I have already cleaned the pilot orifice with the wire from a wire brush and then replaced the pilot and the ignitor, none of which helped. I also have replaced the ignition module, which did seem to solve another problem, but not this one. What might have helped last evening is simply adjusting the angle of the pilot, which I noticed was mounted maybe 15 degrees from the original position. Assuming that the gas, being lighter than air, will rise straight up, then the new position puts more of the electrode in the path of the gas flow. However, even after doing that, last night on one occasion it sparked for 4 minutes before the pilot finally lit, but then for reasons I don't understand, the gas shut off immediately after the pilot ignited. Since then, the furnace has probably started perfectly about 14 out of 15 times. It's quite a puzzle, but I'm hoping the spark is too weak and that replacing the electrode wire will fix it.
 
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Old 11-06-11, 11:44 AM
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I'm supposing you replaced the spark module that is either small black box about 2x3" --- the alternative being a flat gray box about 5x6"?

The grey box will shut off the spark if it fails to ignite after several minutes. The black box will continue sparking as long as power is applied to it.


With a new spark module and pilot burner --- that hummer ought to work!

Please describe the size of the pilot flame and how it strikes the side of the pilot burner.
 
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Old 11-06-11, 12:31 PM
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I replaced the gray box (model LH33WZ512A). The pilot flame is blue, about 2 inches high, and at least 80% strikes the right side of the folded metal element (not sure what that is called, maybe safety element or bimetal switch, not sure) and surrounds nearly all of the electrode. The remaining 10% or so of the flame leaks out to the left of the folded metal bit. Oh, I have no idea what you mean by "the pilot burner." Thanks!
 
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Old 11-06-11, 02:44 PM
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The flame sounds OK from what I can tell.

I'd concentrate on adjusting the way the pilot burner assembly (the whole part) is installed --- and you can bend the spark electrode around to find a better position to light the pilot.
 
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Old 11-06-11, 06:52 PM
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Hmmm 2" seems kinda large, did the orifice fall out when reassembling? Also is there any yellow tipping in the pilot flame? If yes and the orifice is installed, I would suggest to once again pull the pilot, remove the orifice and look into the pilot body. You will notice a venturi tube in the center, using a flashlight you will notice a small primary air hole in the tube. Sometimes this hole becomes plugged with lint or a spider nest. To clear take a paper clip, make a 90 on one end and use that to clear the hole. You may want to try this prior to purchasing parts.
 
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Old 11-06-11, 08:18 PM
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Hello Mbk3,


He said he replaced the pilot burner, and most of the time the pilot burner is lighting. That rules out a dirty pilot burner or missing orifice in my book.

My guess is to insure the pilot burner is in the correct position and perhaps a little fine tuning by bending the spark electrode somewhat with a pair of needlnose pliars.
 
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Old 11-06-11, 08:56 PM
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Originally Posted by SeattlePioneer
Hello Mbk3,


He said he replaced the pilot burner, and most of the time the pilot burner is lighting. That rules out a dirty pilot burner or missing orifice in my book.
My guess is to insure the pilot burner is in the correct position and perhaps a little fine tuning by bending the spark electrode somewhat with a pair of needlnose pliars.
Maybe I should pay more attention to what I read. Thanx
 
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Old 11-07-11, 06:42 AM
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Originally Posted by mbk3
Maybe I should pay more attention to what I read. Thanx
Hello Mbk3,


I find myself missing significant facts in a thread sometimes as well. It's easy to lose track of things that have been covered.
 
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Old 11-07-11, 08:26 AM
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Yesterday, I did three things which seem to have fixed the problem: (1) replaced a stripped screw, which is one of only two screws holding the pilot burner to the mounting bracket; (2) adjusted the electrode about 1/32" closer to the burner, so it is now about 1/32" less than 1/4" in that dimension, but still 1/8" away in the other dimension; and (3) adjusted the position of the pilot burner mounting bracket another couple degrees so that the part of the bracket screwed to the furnace is now perfectly vertical.

It's interesting that in all my online research and reading of installation instructions, I never ran across any mention of the importance of the pilot burner mounting bracket being in precisely the right position. Also, if it's that important, I would think it should be attached to the furnace by more than one screw, so that it would be less likely to rotate out of position when bumped or when someone removes the electrode wire for troubleshooting, etc.

Originally Posted by SeattlePioneer
Hello Mbk3,

My guess is to insure the pilot burner is in the correct position and perhaps a little fine tuning by bending the spark electrode somewhat with a pair of needlnose pliars.
 
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Old 11-07-11, 08:55 AM
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Originally Posted by shutchin007

It's interesting that in all my online research and reading of installation instructions, I never ran across any mention of the importance of the pilot burner mounting bracket being in precisely the right position. Also, if it's that important, I would think it should be attached to the furnace by more than one screw, so that it would be less likely to rotate out of position when bumped or when someone removes the electrode wire for troubleshooting, etc.

Experience as a repairman leads you to understand that if things don't work right when you think they should you need to re evaluate what you have done. Often times a missing screw will make no difference ---- but if things don't work it is probably smart to insure that things are installed in exactly the correct way.

Similarly, when a pilot burner doesn't light and there is no apparent reason why it wont, a little judicious bending of the spark electrode might solve the problem --- if you don't break it off and make it worse!
 
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Old 11-21-13, 08:05 AM
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I need help!
I've replaced a 3 wire pilot burner in my gas furnace. The pilot lights but does not start up the burners. When I unplug the 3 wire connector and bypass the white & yellow wires on the unit the burners fire up, blower kicks on and furnace runs through its cycle. As soon as I disconnect the bypass wire... burners shut off with motor still running and blowing ..now cold air. I've replace the pilot ignitor thinking there was a bad circuit in the unit. Unfortunately I've gone through 2 units but they do not seem to be able to fire burners. Any suggestions?
 
 

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