blower motor goes on and off by itself

[Mr Bill]

rob77c -
> No way you know of to test the circuit *

Does this 1993 unit have a * I have sold Ruud for 20 years and I don't think their furnaces with boards show up on the market until about 93/95, you could still have the old adj. fan limit.

- never mind I saw you have a inducer motor. I have seen furnaces act like this with bad stats or shorted low voltage wiring, you can check to see if it's low voltage short by taking all the low voltage wires loose from the board and see if it still does the same thing.

[Freon]

Thank you and a very Merry X-mas to you also, heatseeker. We all learn from each other in this forum. That's the goal.

[rob77c]

I think I'm done with my diagnostics. I removed the thermostat wires, the wires coming in from the AC unit, and the wires coming from the humidifier, and the fan and inducer motor still come on. I'll be ordering a new board today. Thanks for all the help, and I'll post an update once I get the new board in.

[rob77c]

It's fixed! Put the new board in yesterday, and problem solved. Freon, thanks for your able assistance. Happy Holidays to all.

Rob

[how]

Few things will mess up a board and give erratic actions like a loose ground wire. Now the damage may already done but whether you try to stay with this board or move on with the next, I would check out this possibility. This means checking all the green ground wire connections from the board all the way back to the house panel. It can also be a loose ground in any junction box, on/off switch box or in the exterier spiral jacket box connections of your main furnace feed line if that serves as your ground.