I have a carrier forced air furnace. The exhaust fan keeps turning on and shutting off at random. It usually only does it when its warm enough outside that the furnace won't kick on I have the thermostat set at 65 degrees and is 72 in the house there's no need for the heat to turn on but the exhaust fan kicks on and off it doesn't do it all the time either it'll do it for an hour straight and then stop for the rest of the day its not blowing air out of the vents its just the small fan on the front of the furnace it kicks on and off every few seconds, even if I turn the thermostat to off it will still do it. Looked at many forums and they all say it's the circuit board, I don't get it because when its cold out the furnace works fine the fans only come on when the furnace kicks on. Don't know what's causing this.