My home heating & air conditioning fan does not shut off by itself when the temperature is reached. It continues to run constantly.
I had to unplug the cord to get the fan to stop running.

Which fan is it that continues to run all the time. Is it the outside fan or the inside fan?

If this is the indoor blower that you are talking about, Check the on/auto fan switch on the thermostat, be sure it is switch to the "auto" position. If that does not take care of the problem it could be a stuck relay or bad thermostat etc.. If that doesn't fix the problem give us a little more info on the system age, model, gas furnace straight A/C??

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Originally Posted by letmetellu

Which fan is it that continues to run all the time. Is it the outside fan or the inside fan?

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It is the blower fan in the furnace itself, not the outside one.
I unpluged the power cord so the fan would stop. Last night when it got hot in the upstairs I plugged the fan in again and it ran and cooled the upstairs. In the morning I ask my wife to unplug the fan and she said it shutoff when the air stopped. So now it is working again.
Could it be the fan relay was just stuck? And leaving it off for a long while freed it up?

I'd say it's a fan relay, sometimes cycleing the power fixes the problem temporarily, but often it will act up again.

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Originally Posted by hvacservicetech_07

If this is the indoor blower that you are talking about, Check the on/auto fan switch on the thermostat, be sure it is switch to the "auto" position. If that does not take care of the problem it could be a stuck relay or bad thermostat etc.. If that doesn't fix the problem give us a little more info on the system age, model, gas furnace straight A/C???

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I did all the checks on the auto-fan switch and believe it is working fine.
I left the blower fan unpluged for about 5 hours. I plugged in the power again and the air kicked in cooling the upstairs. By morning the fan stopped all my itself again after the cooling temperature was reached. Could it be the relay was just stuck?
It have never seen this before. The furnace/air conditioners are about 13 years old. I live in Arizona so the Air gets a lot more use then the heating. But in any case that unit doesn't get that much use. I have two air conditioner one for the second floor and one for the first floor. Usually, the downstair gets more use then the upstairs.

How hard is it to replace a Blower relay on a gas furnace?

I would need the model of the furnace, but it most likely has a circuit board that the blower relay is built into, the whole board would need to be replaced. I would let it go for awhile, It may be 2 days or 3 years before it acts up again.

Some of the furnaces have a lockout delay when a problem shows up in the circuit board, sometimes they are as much as three hours, so it could be that was the problem. I would wait and not do any thing for a while, like someone said above it could reoccur and if it does we can deal with it then.

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