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 Repairing and Servicing Lennox Products
 Repairing / Servicing Lennox Gas Furnaces
 G20Q3E-75-2 Ignition
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Europa_714

6 Posts

Posted - 12/29/2003 :  1:56:34 PM  Show Profile  Reply with Quote
Hello all,

On above mentioned furnace, started to go longer and longer to cycle on. Found that burner door was open, no pilot. When furnace power is switched off then on again, I can hear igniter faintly clicking but no spark. If I wiggle igniter wire or tap the controller box, I get a strong spark and a successful heating cycle, until next time. Is there a 'test' to confirm that either the igniter or the controller is at fault? is there a spec on the air gap for the igniter to pilot? Is there an expected voltage at the 'ign' terminal when active?
Note: I have checked for all visual clues, terminal corrosion/looseness, 1/16" air gap at igniter, good grounds/power. Limit switches are made, no obvious problems found.
Thanks for any advice.

Europa_714

6 Posts

Posted - 01/02/2004 :  11:34:03 AM  Show Profile  Reply with Quote
Is it common to have an intermittent problem with an igniter? Or is it more common to have a bad controller? I would like to confirm either way before buying any parts, but I am not sure if it is safe to probe the 'ign' terminal on the controller as it seams this would be high voltage, and I am not sure if my DVOM can be used to check this circuit. Anyhow if anyone out there knows of a way to test these parts please let me know… it's been some real long cycles of heat/cool down, here as I can force the system to cycle on, and so far the Michigan weather has been helpful (its 50 degrees here today) but I know that aint gunna last very long in January in Mich..
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Jester

26 Posts

Posted - 01/02/2004 :  8:06:05 PM  Show Profile  Reply with Quote
A dirty pilot assy can cause alot of problems with electronic ignition. Clean with a small s.s wire brush and check all grounds. Also check the location of the ignitor wire.I have found some close to the next burner causing rubbing and ignition ground fault.(You will hear the spark and not see it)I cannot find references to ignitor gap,sorry.
As to the expected voltage, It will be in the ten thousands,even with a spec you would need a high voltage test probe to confirm.
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Europa_714

6 Posts

Posted - 01/05/2004 :  10:30:57 AM  Show Profile  Reply with Quote
Thank You Jester,

That's what I was afraid of, was trying to probe a circuit with too much voltage for my meter, I'm glad I asked first because I might have fried my meter, the control and myself. I will do the suggested cleaning... I have been floating by with manualy resetting the furnace and restarting while tapping and tugging, but the weather in Melvindale is dropping from the 50s to the teens, so this strategy is quickly going down the toilet. Thanks again for the advice, I will post the results.
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Europa_714

6 Posts

Posted - 01/10/2004 :  11:01:43 PM  Show Profile  Reply with Quote
Allthough I never had any real way to test the ignition circuit, I ohm'd -out the igniter, it was OK, but found that the pilot flame was too small also. I ended up spraying the unit down with a 'parts hose' and replaced the igniter (31J35) and the controller kit (53L90)-the kit is great- has Honeywell ignition controller, pilot-with new orfice, flame-sense probe new wires, instructions and even an "update sticker" for the inside cover of said furnace to permanently document the upgrade. After installation I did notice the pilot flame was bigger, so apparently the old orfice was partial clogged. The furnace starts better and faster than what it did with the "Robertshaw" controller. The Honeywell unit seams to be a much more robust unit, the strategy used to ignite the pilot is different, instead of the slow 'tick-tick-tick' of the robertshaw, the honeywell blasts the igniter with fast and strong bursts of spark, starts faster... better unit. Furnace works GREAT and just in time for this wonderful Michigan weather in (-5)s. To all the great HVAC people willing to help others on this forum, I say "Thank You Kindly" even if there is not a lot of detailed help, the moral support and being able to discus and read others with like issues is a great help.
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