I awoke last night to hear the fan running in the attic. When I checked the thermostat it was set to off. I turned on the A/C and then shut it off thinking it would shut the fan down also but it just shut off and the fan kept running even with thermostat in the off position. I finally had to switch off the breaker to get it to go off. When I turn on the breaker it does the same thing. I climbed up into the attic to see if maybe a rodent got up there and was chewing on wires but everything looked clean and fine. I had a problem with my main breaker a couple weeks back and had it replaced because it was only maintaing 40 v not 120v( Old 1959 panel) to some of the outlets. I checked and have 120 everywhere. Could my thermostat have been damaged by the low voltage? Or is the unit itself in the attic broken even though it has the proper voltage? Any ideas?

Fan limit control could be losing its settings allowing the fan to come on in a hot attic.
Stuck relay or defective circuit board.
Open high limit causing the fan to run in the safe mode.

It was only 50 degrees outside and cool in the attic. I am near the beach so it is usually mild temps.

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Originally Posted by htrboy007

I awoke last night to hear the fan running in the attic. When I checked the thermostat it was set to off. I turned on the A/C and then shut it off thinking it would shut the fan down also but it just shut off and the fan kept running even with thermostat in the off position. I finally had to switch off the breaker to get it to go off. When I turn on the breaker it does the same thing. I climbed up into the attic to see if maybe a rodent got up there and was chewing on wires but everything looked clean and fine. I had a problem with my main breaker a couple weeks back and had it replaced because it was only maintaing 40 v not 120v( Old 1959 panel) to some of the outlets. I checked and have 120 everywhere. Could my thermostat have been damaged by the low voltage? Or is the unit itself in the attic broken even though it has the proper voltage? Any ideas?

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It was only 50 degrees outside and cool in the attic. I am near the beach so it is usually mild temps.

Fan and limit still could be defective and the other two items still apply.
You will need to track down the circuits in the unit the check the components to find the problem.

You may have a blower relay stuck closed. Its hard to say with the little info given. How old is the system and what brand is it?

Quote:

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Originally Posted by htrboy007

I awoke last night to hear the fan running in the attic. When I checked the thermostat it was set to off. I turned on the A/C and then shut it off thinking it would shut the fan down also but it just shut off and the fan kept running even with thermostat in the off position. I finally had to switch off the breaker to get it to go off. When I turn on the breaker it does the same thing. I climbed up into the attic to see if maybe a rodent got up there and was chewing on wires but everything looked clean and fine. I had a problem with my main breaker a couple weeks back and had it replaced because it was only maintaing 40 v not 120v( Old 1959 panel) to some of the outlets. I checked and have 120 everywhere. Could my thermostat have been damaged by the low voltage? Or is the unit itself in the attic broken even though it has the proper voltage? Any ideas?

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It is an aire-flo system and was installed 6 years ago. The unit is clean and I checked the low volt 5 amp fuse on the circuit board and it is fine. As soon as I plug the unit in and the thermostat powes up on the wall the fan kicks on but does not show"fan on" on the electronic thermostat. I t also will not signal the ac unit outside to kick on if cwitched to cool. Should I just replace the thermostat and go from there?

If you had electrical work done it sounds like they may have got the polarity reversed going to your furnace. Its an easy fix if this is the problem, reverse the two power wires inside the furnace junction box(power in). If you have black to black and white to white, reverse them black power in, to white on the furnace, white power in, to black on the furnace(KILL POWER FIRST!! ). The newer furnace are polarity correct so if the incoming power is reversed they don't work and with some the blower will run to let you know you have a problem.

Quote:

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Originally Posted by htrboy007

I awoke last night to hear the fan running in the attic. When I checked the thermostat it was set to off. I turned on the A/C and then shut it off thinking it would shut the fan down also but it just shut off and the fan kept running even with thermostat in the off position. I finally had to switch off the breaker to get it to go off. When I turn on the breaker it does the same thing. I climbed up into the attic to see if maybe a rodent got up there and was chewing on wires but everything looked clean and fine. I had a problem with my main breaker a couple weeks back and had it replaced because it was only maintaing 40 v not 120v( Old 1959 panel) to some of the outlets. I checked and have 120 everywhere. Could my thermostat have been damaged by the low voltage? Or is the unit itself in the attic broken even though it has the proper voltage? Any ideas?

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I a ctually didn't have any work done on the furnace or blower electrical. I just out of blue one night was on at 2 in the morning and I couldn't get it to go off without unplugging it. The house did have a failure of the main breaker resulting in it only letting 40v through instead of 120. It was replaced and everything works great but the blower still just runs

Just a stab in the dark with out seeing it but if the problem started after the voltage fix. If it's a older furnace the blower relay contacts may have welded closed from low voltage = high amp draw. If it's a new furnace I would look at the voltage polarity. Either or you will need to get to the unit and check it with a volt meter. If Black wire has 120v its not reversed. Check for 24v from G to C inside the furnace(thermostat wires at control board). If you don't have 24v from G to C it's a bad blower control.(control board or relay with fan limit control.)

Quote:

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Originally Posted by htrboy007

I awoke last night to hear the fan running in the attic. When I checked the thermostat it was set to off. I turned on the A/C and then shut it off thinking it would shut the fan down also but it just shut off and the fan kept running even with thermostat in the off position. I finally had to switch off the breaker to get it to go off. When I turn on the breaker it does the same thing. I climbed up into the attic to see if maybe a rodent got up there and was chewing on wires but everything looked clean and fine. I had a problem with my main breaker a couple weeks back and had it replaced because it was only maintaing 40 v not 120v( Old 1959 panel) to some of the outlets. I checked and have 120 everywhere. Could my thermostat have been damaged by the low voltage? Or is the unit itself in the attic broken even though it has the proper voltage? Any ideas?

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I was ablew to check both of those and both are fine. Is there anything else I can check on my own before I have to break down and pay a professional??