Any furnace guru's?

Burnout68

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How is your air filter
Could be a limit opening then up then closes when cools after burners shut off
What does your furnace do step by step when you start it up
How long do burners stay on
 

Burnout68

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Flame sensor usually can reach with extended nut driver 1=1/4”screw under burners
Then you can fish the sensor out
They really don’t go bad but do need cleaning every so often with some sand cloth or scotchbrite pad
 

Ron H

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My garage unit does not have a filter, the design of this unit has no clearance to get any tool to the screw heads without removing the bracket that looks to be one piece. As mentioned, for some dang reason the sensor screws are behind instead of front access unlike the switches and other components.
 

Burnout68

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How is your blower is it dirty
If to dirty they don’t move the amount of air they are designed to and can cause limits to trip
Make sure all registers are open and the ducts are unobstructed
 

Burnout68

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The flame sensor with the yellow wire going to it
When look at it under burners you don’t see a screw head attaching to that burner mount
 

Burnout68

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It’s tight under there that’s why need a long handle Magnetic tip nut driver don’t disconnect wire it’s easier to fish out with the wire on,can only fit a finger or 2 to try and fish it out it’s usually a L shaped metal rod
 

Ron H

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How long do your burners stay on
When tapping to get it going (mentioned the tap trick in an earlier post) the burners stay on to meet the thermo setting temp. It will complete its cycle fine. When it isn’t functioning right, the blower will run constantly and the burners will infrequently ignite for a around a minute then cycle off. The blower does eventually shut down meaning it won’t run forever; good thing when I’m not home.
 

Burnout68

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yeah usually will try 3 times then will lock out until reset
Sounds more like a limit than the flame sensor
When a flame sensor is giving trouble the burners will stay on for a few seconds only
So I would look for the lack of air flow causing it to run hot and trip on a limit
Especially if system doesent have a filter would look at blower wheel closely
 
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RemCharger

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I see where your coming from Rem, my job was commission based and I had to sell on every job.. six months I walked away.. Safety is first.. A lot of folks can’t fork out that kinda money.. some can’t keep what they have going. It’s a fine line I always believe in looking at it thru their eyes.

If there are cracks it’s time to pay the piper..
I do pick up what you're putting down.
But,, as a vented exhaust unit.. wouldn't the exchanger be under vacuum,, not pressure? And therefore pulling air in, not pushing exhaust out?
Thought the crack deal was more about draft systems.. That's why they created vented
 

RemCharger

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Thanks guys; sail switch or fan inducer I'm unaware of. Does this show up in my top photo of the guts, my OP? Will check for cracks on exchanger - my guess is if this is bad it's time for a new furnace huh? Had one put in the house furnace and was pricy.
The orangey tube from the blower motor to the round sensor. Try taking it off and seeing if water or obstruction in there.
 

Ron H

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I put in a new blower and motor about two months ago. I did this when putzing with the switches. Inspected the vent pipe (it runs out through the garage wall and has a 'T' ending on the vent pipe. Found a sizeable hornets next in the T then though not enough to really impede it, removed the nest and used compressed on the blower end to clear out any debris, didn't find much getting blown out.
 

Demonic

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When it isn’t functioning right, the blower will run constantly and the burners will infrequently ignite for a around a minute then cycle off. The blower does eventually shut down meaning it won’t run forever; good thing when I’m not home.

Sounds like a dirty exchanger, possible cycling on the high limit. You mentioned no filter. Bad idea, that will cause the symptom you describe. Also, the exchanger now runs hot due to a covering of dirt on the air side. Which can lead to a cracked exchanger. As others said, 20 yrs is a good avg life. Make it right before it's a real problem. Find a good HVAC tech that can check draft, fireside, air side rise, manifold gas pressure, clean, etc. Extra points if they use a Dwyer #1227 manometer to check manifold gas pressure.
 

tnfastback

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Guy jumps out of a plane and begins falling frantically pulling at his rip cord. Half way down he passes a guy going up and says “Do you know anything about parachutes?”
The guy responds “No, do you happen to know anything about gas furnaces?” :lol:
 

Burnout68

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I put in a new blower and motor about two months ago. I did this when putzing with the switches. Inspected the vent pipe (it runs out through the garage wall and has a 'T' ending on the vent pipe. Found a sizeable hornets next in the T then though not enough to really impede it, removed the nest and used compressed on the blower end to clear out any debris, didn't find much getting blown out.
Depending how dirty the blower wheel was usually air doesent do it we use a cleaner and water simple green will work on some stuff but if Heavy debris may have to wash then brush it and wash again till clean if that dirty
It’s Common especially if no filter
 
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F4R/T

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There is some pressure I don’t recall psi not much.. but it wouldn’t be able to carry the flue gases out correctly is what ultimately could happen. When the inducer motor turns on there are pressure switches the measure air flow thru. If it builds too much it knows there is a problem and will try a few more times then error out.
 

Ron H

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Yeah, there's a lot involved as possible demons for sure. The old blower wasn't very dirty; but the motor spindle had some excess play causing some noise so figured it wise to get a new unit. Not that expensive surprised to find. Haven't found any water/moisture in the tube. I run this constantly thru the winter keeping the garage around 40 degrees and up it to 55-60 when I'm in the garage...that being most days.
 

Burnout68

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You can measure the air temp in and out see what temp difference you got
On the name plate where model and serial number it should show a temp rise on it
Example: 55-85 degree temp rise
So if your temp difference between intake and supply should be in that range
 

F4R/T

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My folks house has a 1970s AFCO unit in it, never fails just replace blower motor once and it sees regular service from dad and now my brother. I tried to get him to update I looked inside it was clean a pin and big cast iron burners I knew it would probably outlast me. It’s still hummin away.. not as efficient but reliable!
 

Ron H

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Sounds like a dirty exchanger, possible cycling on the high limit. You mentioned no filter. Bad idea, that will cause the symptom you describe. Also, the exchanger now runs hot due to a covering of dirt on the air side. Which can lead to a cracked exchanger. As others said, 20 yrs is a good avg life. Make it right before it's a real problem. Find a good HVAC tech that can check draft, fireside, air side rise, manifold gas pressure, clean, etc. Extra points if they use a Dwyer #1227 manometer to check manifold gas pressure.
The furnace was designed without a filter...seems like a not good thing, but surprised how clean it is especially the ports interior of the exchanger (far as I can gawk at). Flames are steady in unison like rockette dancers.
 
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