I have a Trane XL80 furnace, about 16 years old, with heat only setup. After we turned on the heat, the pilot fire came on, then the furnace lit and the heats up, however the blower wasn't turning and not blowing air.

We opened both doors, saw the fan limit (a little round dial with setting to 150) turned as heat went up and down, and tightened the plugs (especially the one connected to blower motor for the large red wire).

Now, after we put back the blower door (at the bottom which there's a small box with a black botton on the left top), the blower motor started turning, and it CAN NOT STOP!

I tried the trick of "Shut the power off and tap on it with a screw driver handle." but it didn't help. Also probably our model is quite old, I didn't find any LED panel or board inside. Only a small light between the wires on the right side, which was always blinking green.

Changing from blower not turning to constantly turning really confused me. Is this relay problem or something else?

Thanks a lot for your help!

There is a little white button on that fan and limit. Did you accidentally push it in? Or, the tabs on the dial are misadjusted. st tab is fan off (about 95) setond tab fan on ( about 140) abd third one is limit, don't touch.

Thanks a lot NorthernHeat. I'm not sure where the white button is, so I attached the pic for the fan limit. Is it the little silver button b/w the 2nd and 3rd tab?

That one doesn't have one, many do. Just looking at this picture though, if this is taken while the furnace is cooled down, I can see why the fan is still running.