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Old 02-14-2012, 11:21 AM   #1
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furnace limit switch question


I have a 1964 lennox furnace. The problem is the thermostat is not turning on the burner... it was working originally.. I was thinking the honeywell 4064 limit switch is bad. *when i pull out the manual white button on the limit switch it fires the burner and fan comes on..would anyone think it is the limit switch is bad- when its in auto mode???

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Old 02-14-2012, 11:30 AM   #2
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I have a 1964 lennox furnace. The problem is the thermostat is not turning on the burner... it was working originally.. I was thinking the honeywell 4064 limit switch is bad. *when i pull out the manual white button on the limit switch it fires the burner and fan comes on..would anyone think it is the limit switch is bad- when its in auto mode???
1964? 48 years old...........call lennox and see if they want your furnace for the museum.........you may get a free new furnace out of the deal.......

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Old 02-14-2012, 12:11 PM   #3
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furnace limit switch question


Doesn't make sense to me. When you push in that button the power gets applied directly to the fan motor. When you pull it out it returns to just using the temp probe within the exchanger to turn the fan on & off. The limit side of that control is not suposed to be affected by that button.

If a fan circuit connection within the fan/limit control to the temp probe is broken, then pushing in the button would fire up the fan- cool down an overheating limiting furnace and allow the burners to fire up again. You are probably relying all the time on that old limit control(which was only built for occaisional usage) to prevent a house fire.
Get a pro in NOW to see what's what and if the exchanger has been cracked!

Last edited by how; 02-14-2012 at 12:22 PM.
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Old 02-14-2012, 01:19 PM   #4
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furnace limit switch question


Just a guess from a thousand miles away,but Its probably that honeywell 4064 control.
That control is still availiable but you need to know how long the probe that goes into the furnace is.
I may be wrong on this but I waqnt to say that somewhere in the 70's Honeywell switched the fan side with the limit side,so when you get new control make sure you look close at the writing that is embossed in the plastic wire covers inside that control.You also have to look at the little brass piece of metal that goes from one of those plastic covers to the other plastic cover.You may need to cut that connection.
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Old 02-14-2012, 01:27 PM   #5
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Maybe somebody is trying to "pull our leg". Post a pic of the furnace with the front door off so we can see the control etc.
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Old 02-14-2012, 03:22 PM   #6
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go down to the furnace and jump R to W to get a dirct heat call away from the stat that controller should cool off on shut down from the stat being satisfied....pull the silver cover what are the 3 temp.pins set for.do the jump at the unit first then do the same up on the subbase to see if the stat or the wiring is is in question.the honeywell should turn CCW as the heat exchanger heats up
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Old 02-14-2012, 03:52 PM   #7
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Maybe somebody is trying to "pull our leg". Post a pic of the furnace with the front door off so we can see the control etc.
I'm with you.
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Old 02-14-2012, 05:48 PM   #8
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No pics , no proof. Usually flushes em out.
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Old 02-14-2012, 08:36 PM   #9
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one of toes "magic hvac trolls" testing the waters like I hear so much about
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Old 02-16-2012, 05:27 PM   #10
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No need for the wisecracks in here-I have no use for them people. They just take up space...
Ok, so nothing to do with the limit switch.Auto side not working-manual is...
As I mentioned-call for heat not working, So I began again.
I solved it myself. The problem was the transformer.. it was shorting out. Replaced it for $12....Now, no problem... All works as it should.Thanks to biggles, rep, and how, to put me on the right path.
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Old 02-16-2012, 05:51 PM   #11
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Really? You mean it fired on the first try?
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Old 02-16-2012, 06:28 PM   #12
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No need for the wisecracks in here-I have no use for them people. They just take up space...
Ok, so nothing to do with the limit switch.Auto side not working-manual is...
As I mentioned-call for heat not working, So I began again.
I solved it myself. The problem was the transformer.. it was shorting out. Replaced it for $12....Now, no problem... All works as it should.Thanks to biggles, rep, and how, to put me on the right path.
Thats all fine and dandy........but the best advise you got was what you chose to IGNORE...........how is the heat exchanger?

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Old 02-16-2012, 07:14 PM   #13
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funny funny funny......makes no sense at all...not reasonable for standard heating.....
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Old 02-16-2012, 07:23 PM   #14
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Lennox retro circa 1960's.
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Old 02-16-2012, 07:26 PM   #15
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Lennox retro circa 1960's.
now thats a true furnace.....can i get one for my house....

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