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whatshappening 02-09-2010 01:51 AM

Blower cycling and vibration
Lately (the past week or so), the blower in my furnace (GE - at least 20 years old, maybe 30, I'm not sure) seems to be cycling quite frequently and vibrating enough to cause the ductwork to rattle a little. Here's what I've done so far and what's happening. I know very little about furnaces, so excuse me if I use the wrong terminology.
I am not going to include my opinions here because what I think should be the right way, may very well not - I need expert opinions and knowledge. I'm getting pretty worried about this. :(
I removed the blower assembly and wiped it down, though it wasn't really all that dirty. The blower wheel turns very easily and without noise but does seem to be very slightly off center when spinning.
When running, it now vibrates a little less, but that may be my imagination.
When the furnace 'kicks on', first the burners ignite and all 4 bars have pretty even blue flames with the occasional orange lick every now and then. The burners burn for a couple minutes, then the blower motor turns on. It runs for awhile with no noise and a little vibration. Then, the blower motor shuts off but the burners keep burning. After maybe 30 seconds to a few minutes (I didn't time it), the blower motor turns back on. After a while (many minutes - again, I didn't time it), it will again turn off but the burners stay on. This cycle happens about 2 - 4 times each time the furnace is engaged. Finally, both burners and blower motor shut off together.
During this whole time, we are getting hot air and good flow from the vents in the house, seemingly normal.

It has just been the last few days to a week that I've noticed this motor cycling. For years previous, I'm pretty sure that the blower motor did not cycle on/off like this, but I never sat on the floor watching it like I did tonight.
Is this a dangerous situation? Any ideas as to the cause?
Thank you all in advance for any suggestion you can give.

Kurt1968 02-09-2010 04:48 AM

I had the same problem a couple years ago. The fan it wearing out. And out of balance. Mine got to the point where it just flew apart. Had to replace the fan assembly. Better have someone check it out. It keeps cycling because the motor is over heating.

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