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  #1   IP: 99.141.54.35
Old June 20th, 2009, 02:25 PM
okiejay1 okiejay1 is offline
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Default Furnace Blower Motor Runs Constantly & Furnace or AC Won't Run

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!
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  #2   IP: 98.30.163.230
Old June 21st, 2009, 07:13 AM
Mr T's Avatar
Mr T Mr T is offline
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Boards can often be very expensive. A service call and replacment of a cheaper part may be cheaper then trying a board that doesnt fix it (%99.999999999999 of the time they can not be returned)

Your fan switch sounds like it could be stuck. Its often combined with your temp overlimit switch. Its usually around the middle area of the heat exchanger section of the furnace. Try giving that a tap. It sometimes free's it up. If it free's up it may be good, or it may get stuck again. You will need a schematic of your furnace and a volt-ohm meter to troubleshoot it any further. If you decide to replace it, replace it with the exact same part. The over temp limit switch portion is a safety device.
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  #3   IP: 99.150.125.4
Old June 21st, 2009, 02:44 PM
okiejay1 okiejay1 is offline
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Quote:
Originally Posted by Mr T View Post
Boards can often be very expensive. A service call and replacment of a cheaper part may be cheaper then trying a board that doesnt fix it (%99.999999999999 of the time they can not be returned)

Your fan switch sounds like it could be stuck. Its often combined with your temp overlimit switch. Its usually around the middle area of the heat exchanger section of the furnace. Try giving that a tap. It sometimes free's it up. If it free's up it may be good, or it may get stuck again. You will need a schematic of your furnace and a volt-ohm meter to troubleshoot it any further. If you decide to replace it, replace it with the exact same part. The over temp limit switch portion is a safety device.
I have the furnace schematic and a volt-ohm meter. I can understand how the fan switch might be stuck, but would that keep the furnace from running or the air conditioner compressor from running? I think that there is something else either "locked out" or defective that won't allow the furnace or the air conditioner compressor to run. I can provide 24 volts directly to the compressor control wires and get the compressor to run. This doesn't provide temperature control, but since the fan motor now runs continuously, it allows the house to be cooled. I still need to figure out what in the system is not allowing the AC and furnace to operate as it should.
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