Homeowner Cries for Help

I have a old White Rodgers Furnace however this year I go to turn my furnace on and the the heat kicks on and off as it should however the blower stays on and refuses to turn off. I learned if i tap the furnace it goes off every time. If the furnace is not on I can put the the Fan in Auto and On and it will turn on and off but not once the Furnace heat kicks it on then I have no control to turn it off. Please any suggestions. Online i read possible sensor or fan limit switch.

It is definitely your fan/limit switch which is a bi metal coil which as it heats and cools of course expands and contracts and as it does that it turns the controller itself and makes or breaks contact. When they fail the coil does not have the strength to turn the wheel as the wheel corrodes and gets dirty. You may be able to lubricate it with spray lubricant and turn the wheel slowly back and forth a couple of times and get it to work, but to get a new one and replace it is a simple operation and very easy to get to. Just make sure you clip the small wire at the bottom because if your fan circuit is 24 volts which it probably is that wire must be cut to prevent sending line voltage to the control side of the transformer.