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Coleman Blower being weird

Posted: Wed Jan 03, 2018 1:03 pm
by Montanan
Coleman Blend Air Furnace -DGAT075BDD
Because you wrote the definitive guide to troubleshooting Coleman's Blend Air Systems, I would like to submit a perplexing problem for your consideration.
The main blower on my furnace has developed a mind of its own in the last few months. At exactly 4:24 am every morning it will turn itself on for about 40 seconds and then shut off. I have also caught it a couple of times coming on at 12:20 pm, but as I am not generally in the house at that time, I can't say it happens every day. The furnace does not ignite during this event. Only the blower runs.
If I jump up and cycle the circuit breaker it will immediately stop and stay off. The same goes for cycling the switch on the furnace.
The green diagnostic light does NOT flash during this period.
Modification Kit 37323712001 was installed several years ago and other than this blower problem the furnace functions properly.
Blend air system (attic fan, ducting, etc) was completely removed during house remodel in 2010.
Here is my troubleshooting process thus far:
- disconnected green wire (fan) from thermostat. (blower still came on at 4:24am)
-completely removed thermostat. (blower still came on at 4:24am)
- replaced with new thermostat. (blower still came on at 4:24am)
- disconnected all wires from Blend Air Control Box. (blower still came on at 4:24am)
- disconnected "C" wire from I/C board. Wasn't hooked to thermostat anyway. (blower still came on at 4:24am)
- purchased and installed new Coleman I/C Board. (blower still comes on occasionally at 4:24am)
I can't imagine it being a limit switch as I don't get a flashing diagnostic light, the temperature in the furnace closet does not vary more than a few degrees, and the burner is never lit during this event. Where can it possibly be getting any information on what time it is?! I know that the Blend air system was on a 4 hour timed cycle, but as I recall, if power was lost and then restored, it would start the cycle again from that point. The thermostat has a clock in it, but completely removing the thermostat or replacing it didn't change anything.
Any ideas would be greatly appreciated. It's hard enough for an old guy like me to get a full night's sleep, and a wakeup call by the blower every morning at 4:24 am does not help!