Please Help with Suburban NT-30M Furnace before I rip off all my skin.

[berea777]

Hey folks. I'm at my wits end and sure could use some advice. I have an older Suburban Dynatrail Furnace, NT-30M. It starts perfectly, fires and heats like brand new. When the temperature is reached it promptly cuts off the burner and then the blower continues to run, and continues to run, and continues to run, and continues to run, and......(you get the picture). Today I just spent $125 on a new Dinosaur board and replaced the old original board. I must say it starts and runs better, but the blower fan still doesn't ever shut off after the temperature is reached. When I say never shuts off, I mean like an hour later it's still running. I don't understand what the problem is. I assumed it was the board and that's why I replaced it. This unit does not have a separate fan-control relay. Could it somehow be the wall thermostat? I don't understand why that would be. I know some of you will say to just replace it, but it works great otherwise. I recently cleaned the burner out and it seems solid as can be. Help, help, help.

[Minno]

Hi and welcome to the forums!

Will the blower shut off if you turn the thermostat down? I mean after you say set it for 70, and it heats the trailer up to 70, if you bump the thermostat down to 65, will the blower shut off?

Have you tried replacing the thermostat?

[RickDavis]

I am taking an educated guess here without a manual in front of me but as i remember it the sequence when you turn up the thermostat should be, blower comes on, after a time burner lites, the early run is to clear gases from the furnace., when temp is reached the burner shuts down.. If it does this your thermostat should be ok. There is a thermodisk thermostat somewhere near the heat exchanger that comes on when the furnace reaches a certain temp. Once this closes the fan will continue to run after the burner shuts down.. After cool down it is supposed to open shutting off the fan.
This is most likely the culprit. This looks like a piece about the size of a quarter with a couple mounting ears on it and 2 wires.
They are usually marked with a temperature range and are inexpensive.
If I am off base, my apologies. My book for that furnace is not here right now.