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furnace limit switch question

6K views 29 replies 10 participants last post by  beenthere 
#1 ·
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???
 
#2 ·
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.......
 
#3 · (Edited)
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!
 
#4 ·
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.
 
#6 ·
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
 
#10 ·
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.
 
#12 · (Edited)
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?
 
#18 ·
Actually they have the heat exchanger on the 3rd one at our local Lennox distributor, cleaned up and painted nice and silver. Brings back bad memories of removing those old beasts and 200 to 250 gallon oil tanks up narrow stairs in the early 80"s when we got rid of most of our oil and I was strong and smart like Bull.
 

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#20 ·
I have a 55 year old armstrong low boy that side by side efficiency tests by myself and UEI have pegged at 82%. One of those scary units that feeds the vent back through the hot and return air plenum on it's way to the chimney.
Yes I check that vent yearly.
Cheap, quiet & trouble free for the 15 years I've been here.
 
#22 ·
Beenthere..

Partypooper

Not confusing anything. AFUE never graced my post. Just responding to the previous post about another oldie but was pointing out that mine burns amazingly clean, has a second heat exchanger and is even older.
Our industry stands on the dogma that new is better, which coincidently is the veiwpoint that pays most of our morgages. From my perch, things are not so black & white and I try to remember that most dogma is a poor substitute for the not so common, common sense.
 
#23 ·
It also helps that you live in a VERY moderate climate so efficiency is not a big deal. It has got to the point that the gas co who used to do a lot of free basic repairs here won't touch conversion burners in old boilers so like it or not those are going to have to be replaced. Obsolesce gets to everything and everyone. My young techs have never worked on a millivolt system and likely won't get the chance as they are pretty well obsolete. You cannot get cadet fan or limit controls from Honeywell and other parts are going obsolete.:yes:
 
#24 ·
My first install of a progamable thermostat on my furnace turned me into a parts changer before I realized I was dealing with a 6 volt system.

Any generic parts I need have not yet become difficult to get but I think your experience is about 20 years ahead of mine.(weather wear factor).
I'm sure we will probably become one of the last bastions of old parts so let me know if you need anything next time that young parts guy gives you that blank stare..
 
#29 · (Edited)
Older than this guy? LOL. :laughing: Actually that is the latest "hot" new furnace in Vancouver.:yes: I worked on a bunch of those burning oil (Iron Fireman made oil burners too) as well as stokers I guess and they were AWFUL.
 

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