I have a goodman forced air heater. Recently, the squirrel-cage fan will turn on by itself without the burner having turned on first. To eliminate the obvious, I actually completely disconnected the room thermostat from the furnace at the point where it enters the furnace by cutting the wire.

Fan spontaniously comes on for 2-5 minutes then turns off. Half hour later, it does it again. Any ideas? Thanks!

Usually blowers are switched by relays. They are controlled by heat sensors or limit switches depending how old the furnace is. Usually if a relay sticks, it stays on. I would look at the temperature switches on the heat exchanger. It is just a matter of figuring out how it works, and what is bad.

We could be more specific if we knew how old the furnace is.

Furnace was installed in 1995.

That should be new enough to have a temperature sensor connected to a control board. If you are lucky, the high temperature sensor is crying wolf, causing the control board to turn the blower on to relieve the excessive temperature. The temperature sensor should be much cheaper and easier to replace than the control board. If the furnace has a decal with the schematic, locating the correct sensor should be easier.

Maybe your house is haunted...

I replaced the temperature sensor. Problem continues. The fan will randomly turn on during the day for 1 1/2 to 3 minutes every few hours. Are we talking bad control board?