Central furnace fan makes a loud noise when starting up

Discussion in 'Off Topic' started by Howard, Mar 4, 2008.

  1. Howard

    Howard Lifer

    Joined:
    Oct 14, 1999
    Messages:
    47,985
    Likes Received:
    6
    Noise goes back to normal after it's at operating speed. Do the bearings need lube?
     
  2. imported_Greenman

    imported_Greenman Diamond Member

    Joined:
    Jan 23, 2005
    Messages:
    3,372
    Likes Received:
    0
    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.
     
  3. AlienCraft

    AlienCraft Lifer

    Joined:
    Nov 23, 2002
    Messages:
    10,539
    Likes Received:
    0
    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!

     
  4. Midnight Rambler

    Midnight Rambler Diamond Member

    Joined:
    Oct 9, 1999
    Messages:
    4,200
    Likes Received:
    0
    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 ?
     
  5. Rubycon

    Rubycon Madame President

    Joined:
    Aug 10, 2005
    Messages:
    17,546
    Likes Received:
    342
    What does it sound like? Is it a loud hum for a few seconds?
     
  6. Howard

    Howard Lifer

    Joined:
    Oct 14, 1999
    Messages:
    47,985
    Likes Received:
    6
    Kind of, yeah, but it's not a constant sound... ERerERerEReERererERerererErerererERererererererrrmmmmmmmmmm(normal)
     
  7. AlienCraft

    AlienCraft Lifer

    Joined:
    Nov 23, 2002
    Messages:
    10,539
    Likes Received:
    0
    Yes, they have oiling points.
    Only really cheap ones don't.
     
  8. Rubycon

    Rubycon Madame President

    Joined:
    Aug 10, 2005
    Messages:
    17,546
    Likes Received:
    342
    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.