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Old 03-04-2008, 09:26 PM   #1
Howard
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Default Central furnace fan makes a loud noise when starting up

Noise goes back to normal after it's at operating speed. Do the bearings need lube?
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Old 03-04-2008, 09:34 PM   #2
imported_Greenman
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Default Central furnace fan makes a loud noise when starting up

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.
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Old 03-04-2008, 10:33 PM   #3
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Default Central furnace fan makes a loud noise when starting up

Quote:
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!

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Old 03-04-2008, 10:46 PM   #4
Midnight Rambler
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Default Central furnace fan makes a loud noise when starting up

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 ?
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Old 03-04-2008, 10:58 PM   #5
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Default Central furnace fan makes a loud noise when starting up

What does it sound like? Is it a loud hum for a few seconds?
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Old 03-05-2008, 08:21 AM   #6
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Default Central furnace fan makes a loud noise when starting up

Quote:
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... ERerERerEReERererERerererErerererERererererererrrm mmmmmmmmm(normal)
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Old 03-05-2008, 08:24 AM   #7
AlienCraft
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Default Central furnace fan makes a loud noise when starting up

Quote:
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.
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Old 03-05-2008, 03:08 PM   #8
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Default Central furnace fan makes a loud noise when starting up

Quote:
Originally posted by: Howard
Quote:
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... ERerERerEReERererERerererErerererERererererererrrm mmmmmmmmm(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.
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