Central furnace fan makes a loud noise when starting up

Howard

Lifer
Oct 14, 1999
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Noise goes back to normal after it's at operating speed. Do the bearings need lube?
 

Greenman

Lifer
Oct 15, 1999
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Perhaps it's the bearings, could be a drive belt slipping if it has one, might also be a bad capacitor if it's a capacitor start motor. Take it apart and look would be my advice.
 

AlienCraft

Lifer
Nov 23, 2002
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Originally posted by: Howard
Noise goes back to normal after it's at operating speed. Do the bearings need lube?
Most fan motors have oiling points.
You'll need the fan model number and a Johnstone catalog.
They had diagrams last time I did that.

It may be marked. use a light machine oil. fill 'er up!

 

Midnight Rambler

Diamond Member
Oct 9, 1999
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Since the noise subsides after a few minutes of running, I'd agree with Greenman, likely could be the bearings.

If a newer furnace, would the fan motor even have oiling points ?
 

Rubycon

Madame President
Aug 10, 2005
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What does it sound like? Is it a loud hum for a few seconds?
 

Howard

Lifer
Oct 14, 1999
47,989
10
81
Originally posted by: Rubycon
What does it sound like? Is it a loud hum for a few seconds?
Kind of, yeah, but it's not a constant sound... ERerERerEReERererERerererErerererERererererererrrmmmmmmmmmm(normal)
 

AlienCraft

Lifer
Nov 23, 2002
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Originally posted by: Midnight Rambler
Since the noise subsides after a few minutes of running, I'd agree with Greenman, likely could be the bearings.

If a newer furnace, would the fan motor even have oiling points ?

Yes, they have oiling points.
Only really cheap ones don't.
 

Rubycon

Madame President
Aug 10, 2005
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Originally posted by: Howard
Originally posted by: Rubycon
What does it sound like? Is it a loud hum for a few seconds?
Kind of, yeah, but it's not a constant sound... ERerERerEReERererERerererErerererERererererererrrmmmmmmmmmm(normal)

That's normal. The windings hum is augmented at starting (essentially LRA) but the hum is lessened as the amperage drops as the speed kicks up. If the motor uses a starting capacitor and that is going bad the starting period will take longer and become more noticeable.