I have an Armstrong forced air (induced draft) natural gas furnace with central AC (made around 1990 -- Model: EG6H80DC14-1, Serial: A18315MNA). I had a problem at the end of the heating season where the blower motor would run continuously (even when the thermostat is turned to "off"). I thought that I had read that there was a safety feature in the furnace that caused the blower motor to run continuously after the furnace had failed to light for a few times. (A homeowner would notice that the blower was running all the time and call a repairman to fix the problem). If this is the case, how do you reset it?

I now just tried to run the central air, and I still have the same problem with the blower motor running continuously (it constantly runs no matter if the thermostat switch is turned to "heat", "off", or "cool" and the fan switch is set to "auto" or "on"). The only way to shut off the blower motor is to shut off the power to the furnace via the "light switch" mounted on the outside of the furnace. Along with the blower motor running continuously problem, the furnace will not light and the AC compressor will not run when "heat" or "cool" is selected at the thermostat.

I read in the forums to check the transformer voltage to the furnace control board. I am getting 24 volts AC from the transformer to the control board. I tried jumping the "R" and "Y" terminals on the control board, but that did not start the AC compressor. There appears to be a couple black boxes (relays?) identified as K1 on the control board and a different black box as K2 on the control board. I tried gently tapping on them with no change. I also disconnected and reconnected each wire to the control board one at a time, but that didn't help solve the problem.

The control board has Heatcraft 38493B001 printed on it, but I have not had any luck "Googling" that number. Does anyone know what the replacement control board is for this furnace?

Also, does anyone have any other ideas on what to do to solve the problem of the blower motor running continuously and the heating and cooling functions not working other than replacing the control board?

Any suggestions are appreciated.

Thanks, in advance, for your help!

Sounds like you may have limit problem if it has doen this sense the end of heating season.

Sounds crazy but have you changed the batteries in your thermostat. I have seen a lot of customers who have an issue like this and all we needed was to change the batteries in the thermostat.