Old Carrier 80U-19A furnace. Blower randomly turning off and on

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Old 02-21-19, 09:09 AM
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Old Carrier 80U-19A furnace. Blower randomly turning off and on

Working on my father's old Carrier 80U-19A furnace by "BDP Company Division of Carrier Corporation". Blower randomly turning off and on. Burner is on all the time when we set the thermostat to 85 but the blower will come on and it would turn off after 10 to 20 mins, rest for a few mins, then turn back on and repeat, sometimes after 30 mins or 1 hr.
We made sure all the vents are open. Air filter is new.
It is a stand pilot. I see the little flame 24.7.365.
So, not the thermocouple because the burner keeps burning, right? Limit control (if this furnace has it)?
It seems like there are many different designs. I spent hrs researching. I could not come up with any conclusion.

Is there even parts available for this 1970's furnace? I could not find a part diagram for it. Can those universal parts work on this?

BTW, thermostat is new. It is a simple heat only digital non-programmable 2-wire Honeywell TH1100DV1000.

Thanks in advance.

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Old 02-21-19, 09:31 AM
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Motor cycling on thermal overload or fan/limit switch cycling blower due to furnace not producing enough heat (underfired - gas pressure off or orifices plugged), out of adjustment, or failing.

Don't change parts until you know what's wrong.

This unit needs a thorough heat exchanger inspection, it's probably cracked. A new unit would have up to 1/3rd on the gas bill and be safer.
 
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Old 02-22-19, 08:48 AM
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Thanks for the input.
We in Northern California really don't need it. We have not used it for over a decade and this year we want to turn it on for the past cold week.

Time for a new one.
I still want to understand how all the components work but I guess there are so many kinds and it is not worth digging up this info.
 
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Old 02-22-19, 09:38 AM
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Let me still ask.
What if we keep on using it? It does warm up the house but sometimes it will not blow for 5 - 10 mins.
If the heat exchanger has a crack, then CO will escape out and get into the vents?
Blower cycling would not be the indication of a cracked heat exchanger, would it?
As long as the house is not filled with CO, I think we will keep it and use it only for the coldest days (down to 40F).
 
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Old 02-22-19, 12:30 PM
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If the heat exchanger is cracked, yes, it will put CO into the house. Any house which has any kind of fuel burring appliance should have CO detectors.

Blower cycling would not be an indication of a heat exchanger crack.

The black box above the burners looks like a fan control made by Camstat. The chances of finding one, if that's the problem, are somewhere between slim & none.
 
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