I have a Bryant furnace Mod. #394GAD024050 and after the temp has reached the set point and the furnace has cycled off the fan will come back on a couple of times for approx. 2 or 3 seconds. In the older furnaces with a machanical fan/limit switch some times the temp would creep up and cause the fan to come back on for a few seconds. My question is what energizes the heat relay on this type of furnace with the control board and why would the fan just come back on a couple of times? It seem to do this when the heat cycle has been around 10 minutes.
Lamar

The fan sensor or control is out of range or defective. Look on the back side of the blower door for a wiring diagram to locate this part. As long as your air filters are clean and all registers/cold air return ducts are open then the sensor/fan control disc is bad.

This model controls the fan via the electronic circuit board, so no mechanical adjustments/calibration are possible. The heating-speed blower relay is energized to turn the blower OFF, so several possibilities exist. Is main burner operation sustained throughout the heating cycle?

To KC13, yes the main burner operates throughout cycle. Everything is normal except for the cycling back on of the fan.
Lamar

Try this: Remove the blower access panel, and the cover from the circuit board enclosure (if present). Does the circuit board have 2 "ice cube" relays? If so, observe the relays while pressing in the access panel interlock switch. You should see the heating-speed blower relay open. Next, tape the blower door switch in, operate the unit briefly, and observe the relays for visible arcing at the end of the cycle (darkening the area around furnace will aid visibility). Post description of what you observe.

Thank you KC13, I will check this out next week as I will be out of town a few days. When I do I will be sure and post the results. Until then, again, thank you.
Lamar

This is not an answer, but another question on the same subject. I have a bryant furnace model 394gad036125 and am having the same issue with the fan through post #4. I have not tried KC13's suggestions in post #5 yet, but will when I get home. I have one additional issue, though. Each time I press in the access panel interlock switch, the control board seems to emit a flashbulb like light. I have not taken the cover off the control board yet, but the spark/flash is quite evident through the sticker/label that covers the control board cover. I called my HVAC guy and he said that the entire control board needs replaced and would be around $250 for parts, labor, and travel. I am always hesitant when someone provides a diagnosis over the phone. Does this seem right? And, isn't this something I could replace myself, if parts dealers would sell to residential consumers?

Thanks in advance.

The heating-speed blower relay on the board is actually powered open to keep blower off. When power is applied, the flash you see is the relay opening just as power is introduced. Not unusual, I see this almost every day.

Thanks for the help. I let the furnace repair man put in the new control board. It seems that he called the local Bryant parts dealer, who also diagnosed the problem. It all seems to be working well. The cost was as stated above plus taxes.

Thanks again.