Furnace just quits

pecmsg

Is that limit still bypassed and out of the cabinet?

josephny

Heck no — limit switch is replaced with a new one and fully installed. I may be stubborn but I know enough to listen to the experts!

josephny

Jamie Hall said:

The bottom trace is power consumption? Staring you in the face. Looks like a motor is jammed or its start capacitor is toast. Question is, which one?

Yes, bottom trace is electric consumption.  

I was thinking motor and/or capacitor also.   

Investigating now….

HVACNUT

Agree with @Jamie Hall. Even with the auxiliary limit removed, the burner wouldn't start presumably because the burner circuit was open on its primary limit. Once the temperature in the heat exchanger drops, the burner will start. But without the blower motor, it won't be on for long. 
Your buddie with the meter, can it test microfarads? 

mattmia2

Watch the burner as the blower comes on, the flame shouldn't change. If it does the heat exchanger is rotted out and probably causing the burner to lock out. I think that is common on these and is likely to kill you with co poisoning. You need to turn it off immediately and do not use it if that happens.

josephny

Flame does not change once it's on.

But now I'm confused again: Furnace was running (cycling) okay, so I lowered the set point to 45 and the flame went out and a couple minutes later the blower fan went off. But, the burner motor keeps running. It's been about an hour and the burner motor is still running (still with no flame burning and no blower motor running).

After the hour, I raised the setpoint and the furnace fired up properly.

But, the burner motor never stopped running even when the furnace was not firing.

Could someone please explain to me what controls the burner motor? That is, is it supposed to stay on after ignition (the flame) is off?

109A_5

Hello @josephny,


The "Dead zone" is when it stops working. But what is the delay of minimal electric draw, the "Dead zone" delay time ? Probably not a seized motor. And what is the later higher draw ?

I would think with a seize motor there would be no "Dead zone".

To troubleshoot you probably need a multi-meter and know how to use it, something is interrupting the call. Is there 24 VAC between W and C on the control board when dead ?

109A_5

Hello @josephny,
The control module controls the burner motor, Red wires PSI, PSO and Black wire IND. And the fan switch controls the Blower motor. Would need to know the Make and Model of the control module to possibly understand better.

josephny

I think I figured it out.

After quite a long time, the burner motor stopped. I then raised the setpoint and the burner motor would not come back on.

So, with nothing but a hunch, I opened the top of the black wiring box attached to the burner motor to see if there were any visible problems. I touched a couple of wire nutted wires and the furnace kicked on.

I proceed to redo the wire connections, but that did not fix it.

I then looked at (what I now know is) the time delay relay and sure it it has lots of corrosion in it. Cleaned it up and now it seems to be working. So, my working theory is that this is the fauly part and the contacts were not opening and closing as they are supposed to.

I've been googling for the right part, but can't find it.

Numbers on the relay are:

12s20
H1-30
L8919
304987
H24v
C30-60

Does my thinking make sense?

Does anyone know where I can order one of these online?

Thank you.

Jamie Hall

Certainly might be part of the problem -- but I'm still concerned about the waveform of the current draw in the latter part of your graph. Something is trying to start -- and perhaps finally does -- and then something else with a much higher than normal current draw is trying to start and, it would appear, doesn't.

josephny

Jamie Hall said:

Certainly might be part of the problem -- but I'm still concerned about the waveform of the current draw in the latter part of your graph. Something is trying to start -- and perhaps finally does -- and then something else with a much higher than normal current draw is trying to start and, it would appear, doesn't.

I should have explained in more detail. The electric usage is recording for the entire house. The lights were all off, but there is still a fridge running, an electric hot water heater that (without hot water usage) kicks on twice per day for a few minutes, a well pump that also wasn’t on. 

So, the 100-200 watts continuously being used can be safely ignored. I confirmed this by totally powering down the furnace. 

The large spike are the electric heaters I have at the ready given the unreliability of the furnace. 

The square wave form showing during the normal cycling, I believe, is exclusively the furnace. I just don’t know exactly which components. 

That said, I’m not certain of anything, let alone that the time delay relay was the cause of the furnace failure. 

109A_5

Hello @josephny,
The numbers in the picture seem to match yours.
https://www.starsupplyusa.com/products/nordynemillerintertherm-104381-time-delay-relay

josephny

109A_5: Thank you!

josephny

12 hours later....
.




.
And a close up...
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109A_5

Hello @josephny,
Hopefully that was the problem !!!

"and sure it it has lots of corrosion in it."

What caused the corrosion ?

josephny

109A_5 said:

Hello @josephny,
Hopefully that was the problem !!!

"and sure it it has lots of corrosion in it."

What caused the corrosion ?

I don't know.

There has not been any water-exposure that I'm aware of.

Does 25+ years of use not fully explain?

I do have another theory, which I'll obviously share, but might as well preface it by disclosing that I am fully aware (and dismayed) that sharing it moves me even further (if that is possible) into the 'PITA DIY homeowner' classification (as opposed to the more desireable 'competent non-pro' category):

Just a couple months ago I installed an Ecobee on this furnace and I had mistakenly wired the power to the transformer that fed the Ecobee from a circuit inside the control box that was switched by the controls of the furnace. Basically, the furnace was cycling the power to the Ecobee every 10 minutes. So, my theory is that a few weeks of this was just too much for the delay relay and it couldn't handle this. I don't know if this makes sense, because this relay is supposed to be opening and closing many, many times per day. The theory is the result of an over-active imagination, which occasionally lands on the truth or a solution.

BTW, replacing the entire pilot/ignition/thermocouple assembly, I'm pretty sure, was overdue -- massive deterioration/corrosion there also.

For now, it's working.

Thank you all so much!

PS: Yes, I'd really really like to be more capable of everything heating-related.