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I was working on my brother's electrical panel for another issue and turned on power. I just thought furnace was kicking on but after a little while he noticed it was not blowing heat and the fan will not shut off until the furnace is shut off, the green light is flashing 4 times as well. He shut it off at the furnace and as soon as he turned back it back on the fan immediately kicked right back on he tried this twice with no change. I am really not sure if that's what it did when I turned on the power or if it heated for a while then just kept the fan running or what. I was kind looking for any suggestions what to look for before I head back down his way.

Hi Wade,


Probably a stuck fan relay on the control board keeping blower running.


Test across W and C on the board for 24vac. IF you read 0vac, then test across Heat and a neutral for 120vac.


IF you read 0vac at W and C, BUT read 120vac at Heat and Neutral, the board is bad.



Thanks,
Robert

Hi Robert,

Thanks for the quick reply the board tested out ok, it was the limit switch right by the blower. I am guessing the furnace was running when I killed the power and it overheated just enough to pop it. I will have him keep an eye on it for a few days to make sure. Thanks again for your input this site is very helpful you have steered me in the right direction a couple of times now and saved me a lot of time and money in the process.

Hi,

The upper limit switch turns the gas valve off if overheating occurs due to dirty furnace or blower not working.



Thanks,
Robert