Central furnace fan makes a loud noise when starting up

[Howard]

Noise goes back to normal after it's at operating speed. Do the bearings need lube?

 

[Greenman]

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]

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]

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]

What does it sound like? Is it a loud hum for a few seconds?

 

[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)

 

[AlienCraft]

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]

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.