Was at Mom's house today and noticed that her furnace fan makes a kind of
vibrating/humming noise the first few seconds as it starts up. It's a Gas
furnace (Trane) and a 10 year old house.
Recently I had to replace the blower motor in my 22 year old Trane and
cleaned everything. When I start my fan, there's an initial buzzing from
the transformer and the fan comes on right away. The transformer buzzing
gets quieter after 2 seconds.
I know that blower motors may need oil from time to time, but then if it's
in need of lube, why does it make a noise only on start? After it gets
spinning I only hear air blowing.
The noise from Mom's sounds "wobbly", very much like a fan that isn't
aligned or attached right but then evens out from centrifugal force as the
Could the blower have come a bit loose from the frame or the frame from the
housing? I won't be back there for a few days but wanted to get some ideas
on what to look for if possible. Or could dust just be gumming up the works
and making the motor work harder. I'm not sure if it's ever been cleaned.
Also, the labored startup of the fan seems to last a little longer each
time, like whatever is going wrong is getting worse.
The blower and fan set up is as simple as one can get. Just
disassemble the motor and fan assemblies and do a thorough cleanup and
the furnace will be good for another ten years or so. The maintenance
stuff to look for will be the fan's axle and axle bearings. I had
overtightened my fanbelt before and this caused the shaft to wear into
the bearings and ovalled it. To correct the fan's startup and stop
"clunk noise" I tightened the fanbelt further. This of course caused
further wear. By the time I took the fan assembly apart the shaft had
worn down more than half its diameter, and the bearring holes
oversized. Should you replace the axle and bearings do not add any
lubrication. The bronze bearings are meant to run dry. Lube,
especially grease is commonly dried by the heat. This caused the
bearings to sieze.
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