When central AC is on, induction fan on my high efficiency Gibson/Nordyne furnace won't shut off. The yellow and red lights on the board stay on. The furnace cabinet says that a continuous red light indicates a "false flame or gas valve relay shorted". I can hear the pressure switch click on when I turn the power switch on, so I don't think that is a problem, but am not sure. If I disconnect the leads to the temp sensor on the plenum or on the induction fan housing, there is no effect on the fan. Disconnecting the leads to the gas valve has no effect.

Reading more, I see that a steady red light means it is OK. The cabinet instructions are kind of confusing on that. "Continous" apparently means continuously flashing. So, maybe the yellow light being on steady indicates detection of a flame? Since it is in cooling mode, there is no flame, but maybe that is why the induction fan won't go off? I have to believe it is a faulty temp sensor or pressure switch?

Ok, now I have disconnected, one at a time, the temp sensor on the mini-plenum, the temp sensor on the induction fan housing and the pressure switch and then jumped the wires of each of these with no change - the induction fan continues to run. I also removed, emery sanded and replaced the flame sensor probe. It seems that the board is sending a signal to the induction fan to stay on. Is it likely that the board or a relay on the board is bad?

Good thinking


Quote:: Is it likely that the board or a relay on the board is bad?

A new board is on its way. I will let the forum know if this solves the problem.

A new board is on its way, but will take a while and I will be away from my home for a couple of weeks. In the meantime, can I leave the inducer fan disconnected while the furnace is in cooling mode?

You could disconnect the wires sending power to the induction motor,, be sure to tape off ends good so they won't short against anything

Thanks, WM. I guess my question is: Is there any reason that the inducer fan must be connected when furnace is in cooling mode? I have unplugged it from the board and the system seems to be working fine. I don't see any condensation in the small plenum where the burners are located.

No,, no reason, its not needed in the ac mode

To close out this discussion, I got a new Nordyne board (common to a lot of furnaces), installed it and the system seems to work perfectly now in both heating and cooling mode. I immediately noticed that the yellow light is off. That light is identified as "Flame" on the board. I mentioned that this light was on in my first post, but no one picked up on that and I now realize that the inducer fan was on because the system was mistakenly thinking there was a flame in the burner. Since I did not install a new flame sensor, the problem was in the board.