Furnace blower coming back on

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  #1  
Old 01-14-11, 05:39 AM
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Furnace blower coming back on

I have a Bryant furnace that has started having some issues. It runs fine and heats the house fine. The problem comes when it gets to the thermostat's set temp. The blower stops, but then 2 seconds later comes back on, runs for 4-5 seconds and shuts back off until the next cycle. On rare occasions, after coming back on the first time, it will come back on a second time for another 4-5 seconds and then shut off.
It is a Bryant furnace, model number 394 GAD 036075 Series F. It is a fairly old furnace. It was put in new when the house was built 20 years ago.
Like I said, the furnace runs fine and heats the house just fine. I have a feeling that the constant on and off with the blower cannot be good for it and I would hate to shorten the life of the furnace unnecessarily.
Any help on this matter would be greatly appreciated.
 
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  #2  
Old 01-14-11, 07:59 AM
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The manual for your furnace is at:

http://www.xpedio.carrier.com/idc/gr...i394g-25-1.pdf


Your furnace fan is controlled by the circuit board, which has a solid state timer which delays the fan shutoff after the burners turn off.


The short answer is that you shouldn't be experiencing the fan turning on again as you describe, which indicates that the circuit board is starting to fail in that circuit.

Probably that will continue to get worse until it quits working in some way.

I wouldn;t call it a hazard, but the general rule is that a furnace should be repaired so that it operates as designed.

Not a bad DIY job if you want to replace it yourself. I have this circuit board for sale for $80 left over from my now closed furnace repair business. I could post it on Ebay if you are interested in replacing the board.
 
  #3  
Old 01-15-11, 12:19 PM
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i found this post in a different forum, but it's from a couple years ago, so replying wouldn't do me much good:
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.
When I pressed the access panel interlock switch I saw the heater relay spark. I ran the furnace while the switch was pressed in. The heat came on, then the relay sparked and the blower came on. It ran through its cycle and got up to the thermostat's set temp. The heat shut off and the blower stayed on for another ~30 seconds. The blower shut off, about 3 seconds passed, the relay sparked again and the blower came on for ~2 seconds. It shut off, another 3 seconds passed, the blower came back on for ~2 seconds, and then shut off.
I don't know what any of this means, if it's normal or not, but it's what I observed.
I do like the idea of being able to change out the circuit board myself and is something i think i could do. The only concern I have is that I live in Ohio and it is currently the middle of winter. If I were to attempt to change out the circuit board and screw something up (which is a definite possibility) i would be without a furnace until I could get someone here who knew what they were doing.
 
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Old 01-15-11, 01:02 PM
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It's an edge connector that plugs in at the top of the circuit board and screwing in the wires from the thermostat and such at the bottom of the board.

It doesn't amount to much, but you certainly are free to decide if you want to do it.
 
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