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Odd vibrational noise from blower(?)...

wcweaver3 Member Posts: 44
Hi there,
I have a 2300 square foot home served by a Unico AC system with a 3 ton American Standard compressor outside using R22 refigerant. The unit was installed 17 years ago (2005). The current American Standard unit is an Alligence 14, model number 2A7A4036B1000AA. This is a totally seperate system from the my hot water boiler heating system.

During the cooling season, I leave the fan on all the time and the compressor will cycle on and off based on the thermostat temperature. No problem there.

When I turned on the system for the season, I noticed an occasional vibrational noise upstairs. It sounded exactly like someone was using a pressure washer outside. I looked around and saw nothing. I traced it back to the AC mechanicals. For this system, only the duct work is in the attic. The coil and blower fan are in a bedroom closet (photo included). This bedroom closet buts up right next to, and I think goes over, the main home stairwell. When you go into the closet, you just hear a normal fan noise. However, the stairwell kind of acts as an ampitheater and magnifies the vibrational noise. You can really hear it in the stairwell and in another bedroom and kind of drives me a little nuts.

While the noise is exactly the same every time, and doesn't vary in intensity, when and how often it occurs is random. It can last anywhere from 5 minutes to more than an hour. It will happen 2 to 5 times a day. Additionally, it doesn't seem to be connected in any way with the cycling of the compressor. Sometimes I hear it when the compressor is off and sometimes when it's on. It doesn't seem to matter.

Any thoughts as to what might be failing?

Thanks very much!


  • Jamie Hall
    Jamie Hall Member Posts: 21,526
    Sounds like something affecting the fan -- but what is hard to say. It could be slightly out of balance. It could be some dirt on a blade. It could be a failing bearing. It could also be something slightly loose in the ductwork and fan casing which moves in an out of the way, affecting airflow to the fan.

    Good luck...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 8,382
    I had this problem which turned out to be bad motor bearings in the blower motor:

    Check the play in the motor bearings both up and down and front to back. Mine had no play front to back but a ton of play up and down where the weight of the blower was on the bearing and if i recall a lot of endplay.
    EBEBRATT-Ed Member Posts: 13,779
    In addition to the above check the blower wheel for any plastic or plastic bag that may have got sucked into it. Also check for dirty filters
  • Big Ed_4
    Big Ed_4 Member Posts: 2,368
    It is good practice to change the motor , cap and wheel together ....
    I have enough experience to know , that I dont know it all
  • wcweaver3
    wcweaver3 Member Posts: 44
    Much good advice! Thanks so much for the guidance!
  • clammy
    clammy Member Posts: 2,983
    . Possibly one of the armaflex insulation panels either on the blower compartment or coil may have come off blocking air flow and causing noise and the vibration . Or as other have stated check the blower motor for end play and possibly a loose blower wheel or blower housing mount may be loose . It looks like you could use a condensate trap on out coil outlet . I have heard condensate pans holding water making noise as they attempt to drain either till the pan is completely full of water or the blower shut off then the pressure differential is gone and the pan drains . Do yourself a favor and install a trap ,it should have been installed from day one it s in the directions from unico .
    Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating