I have a furnace with the B18099-13 control board. The fan blows constantly whenever power is applied. The status LED on the control board indicates "OPEN LIMIT SWITCH"

Where are the two limit switches located? On board or off? Are there any tricks, quick-fixes, or "band-aids" for this situation or will I need a new B18099-13? I only ask because, as usual, this has happened on a Sunday and none of the electrical supply places are open.. . and it's pretty chilly in here.

Thanks in advance. Any help will be appreciated.

Tom

Fortunately the limit switches are near the combustion chamber, not on the board. I would expect a normally open switch, but the error sounds like a normally closed switch.

Follow the wires running from the board to the heat exchanger. Limit switches are often sort of oval with 2 wires, maybe even 3. They are located someplace that get hot when the furnace is on. If you can find a schematic, it may even show the wire color. A normally closed switch will look kind of like this, __._.___ , and a normally open like __./.___ If the switch is bad, or a wire disconnected, it will tell the board the furnace is too hot shutting the gas off and leaving the blower run. You may be able to identify the problem by connecting the wires to each other. If that relieves the code, take the switch to an electrical supply and let them choose a new one.

Something went wrong. You may be able to get the furnace to run by leaving the wires connected. However, that way, the next time something goes wrong, the furnace could over heat and burn the house down. I hate to point this out since most people are sensible enough not to do that.

The limit switch could be open for something as simple as a dirty filter or cooling coil, or a blickage in the flu pipe

Thank you both for the replies. I found the limit switch by tracing the red wires from the edge connector like you said, labman. It was simply a little dirty.

Removed it, gave it a quick contact cleaner bath, works fine now. Actually cleaned the furnace top to bottom. I'm going to get a spare limit switch just in case that one is going bad.

Thanks again lads.

Tom

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Originally Posted by hawkeman

I have a furnace with the B18099-13 control board. The fan blows constantly whenever power is applied. The status LED on the control board indicates "OPEN LIMIT SWITCH"

Where are the two limit switches located? On board or off? Are there any tricks, quick-fixes, or "band-aids" for this situation or will I need a new B18099-13? I only ask because, as usual, this has happened on a Sunday and none of the electrical supply places are open... ...and it's pretty chilly in here.

Thanks in advance. Any help will be appreciated.

Tom

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Tom,
I have had the same problem with the same board (B18099-13) on my Goodman Forced Hot-Air system. Only the status light is showing normal. When not calling for heat, the blower still runs blowing cold air throughout the house. I suspect the board will need to be replaced. I located one for under $100. Let me know if you need the info

Mike St. Pierre

Hi All, so once we find the limit switch needs to be replaced, where can the replacement parts be ordered on-line at a reasonable price? Thanks!

My furnace fan continuous runs never stop , either heat or cold off. It continuous runs 24/7 , I have no selection on thermostat board to turn it off,
Is it normal that fan runs all time even the ac turn off or heating burner turn off.?
The mechanic says may be fan switch is faulty, I am confused, please help me.