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Old 11-06-2011, 11:14 AM   #16
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Intermittent blower operation


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Originally Posted by biggles View Post
just to think if the pilot gas feed is leaking it will always be lit from the main burner and stay lit after burner goes off
I like this. If the pilot gas feed is leaking, that might explain the unusual pilot flame size and excess heat, blower activity, etc. And the flame, which looks to be aiming away from the thermocouple could prevent the burner from lighting, maybe? Hmmm...

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Old 11-06-2011, 11:34 AM   #17
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Intermittent blower operation


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see the pix of that 2 wire limit stamped 180F remove it and clean what i think is a heat resistor looks like a fan limit,but not a hi limit where it is located...
Will do.

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i see the roll out on the upper left disc where is the other limit....up in the heat exchanger?is there anything else above the burner with a pair of wires on it and a temp valve showing.
No. I only found those 2 shown in the pix wired in series and I traced the wires back to the control board to confirm. The schematic shows 3 switches in series, labeled ALS, LS and ALS. The schematic has a red wire from the board to the first ALS, a red wire from first ALS to LS, a violet wire from LS to second ALS and a violet wire from second ALS back to the board. What I found in the unit is a red wire going from the board to the switch over the burner, a red wire from there to the one marked 180, and a violet wire from the one marked 180 back to the board.
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Old 11-06-2011, 12:43 PM   #18
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Intermittent blower operation


Some of those older units you have to pull the burners out and there'll be another limit deep inside. Of course you'll see wires leading to them if that is the case.

Or you may have one on the end of the furnace itself, like a fan limit or on the blower housing itself.
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Old 11-06-2011, 01:21 PM   #19
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Intermittent blower operation


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Originally Posted by Doc Holliday View Post
Some of those older units you have to pull the burners out and there'll be another limit deep inside. Of course you'll see wires leading to them if that is the case.

Or you may have one on the end of the furnace itself, like a fan limit or on the blower housing itself.
Thanks for the heads up. I was sure there was another one hidden somewhere - especially since it's on the schematic - so I checked everywhere, including the blower housing. No dice. The wire trace exercise confirmed only 2. No mystery wires unaccounted for.

Last edited by Illroy; 11-06-2011 at 01:26 PM.
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Old 11-06-2011, 01:55 PM   #20
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Intermittent blower operation


In the pictures you provided, one switch is to a backing plate. Is there another plate visible with teminals but without any wires to them? Many times certain (hack) techs will simply remove a switch from circuit.
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Old 11-06-2011, 08:03 PM   #21
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Intermittent blower operation


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Originally Posted by Doc Holliday View Post
In the pictures you provided, one switch is to a backing plate. Is there another plate visible with teminals but without any wires to them? Many times certain (hack) techs will simply remove a switch from circuit.
LOL! Yeah, I was on the lookout for that - but I didn't find one.

Meahwhile... I've pulled out the limit switch assembly with 180 printed on it as suggested and it was clean. Next, I pulled out the pilot/ignitor assembly to check for gas leak and in the process found that it is not only NOT leaking gas, but the flame is aimed right across the thermocouple as it should be. I guess it just puts out a big flame - seems overkill, but what do I know. FYI, when it was stuck on, the thermocouple tip was red hot, and as I said before, just the pilot alone was putting a good amount of heat into the burner chamber.

I've been searching the intarwebz for 2 days looking for info about pilots stuck on and only found info about pilots stuck off. I did stumble across someone whose fireplace thermocouple was causing a similar sympton, so I removed it and cleaned the tip and disconnected/reconnected the sensor wire as he did to solve his problem.

Now the pilot shuts off after ignition every time, the blower starts and stops when it's supposed to and the whole system is cycling normally

My wild guess it that the thermocouple was not responding correctly in order to signal the ingnition module to shut off the pilot valve. Assuming the ignition module needs a shut off signal from the thermocouple in order to reset for the next burner ignition request, that might be why the burner would not restart until I manually turned off the pilot and let it cool down. And the heat build-up from the overheating pilot may have been why ther blower kept kicking in erratically.

Let's see what happens during the next week. Knock wood...

Hope someone else finds this useful.

Thanks again for your input!

Last edited by Illroy; 11-06-2011 at 08:07 PM.
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Old 11-07-2011, 09:09 PM   #22
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Intermittent blower operation


Hey Doc. Guess what I found? Yup. Limit switch #3 - on top of the blower housing buried under a layer of dried out fireglass insulation

Biggles, you're right too. Pilot wasn't triggering the limit. That takes care of the intermittent blower issue.

Still have the pilot/burner issue though. About every third time, the pilot won't shut off and have to manually reset pilot valve to get the burner to light. I replaced the flame sensor. Same problem.

I've heard this is a typical failure for the blue Johnson ignition modules. Mines an LH33CZ006. Is there a Lennox cross for this? Will the 30W33 http://www.pexsupply.com/Lennox-30W3...FQNShwodzlbzBA work?

Thanks again guys.

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