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  1. #1
    Join Date
    Jul 2008
    Posts
    11

    Low pitched hum from furnace blower when AC cycles on

    Hello all. Glad to be a new member of the site. I have a 15 year old York furnace, mod#P2MPD14N08001B 115v-1PH-60hz. The York A/C unit was replaced about 3 years ago with a Frigidaire FS5BD and evap coil C3BA-048. At the time the A/C and evap coil were replaced, the tech also removed the blower wheel for cleaning. One thing I've notice since the repacement A/C and evap, is that everytime the A/C cycles on I can hear a low pitched hum resignating up through my bedroom floor as my 8'X8' utillity room is just below. The noise is only present when the A/C is on. With just the fan in "on" or with heat during the winter, I do not hear it. At first, I thought it was sound resinating from the outside unit that's located just below my bedroom window (one story down), but when I place my ear directly to the floor carpet area where the furnace is located just below, the hum can be heard loud and clear. This past weekend, I replaced the 15 year old blower motor and run capacitor thinking it might be showing it's age with noise, but the hum is still present. I thought that I could live with it, but I'm a light sleeper and find the hum somewhat annoying everytime my A/C cycles on, while trying to fall asleep. Any input would be greatly apreciated. Thanks

  2. #2
    if sound is not present without cond unit running sound like a possible vibration in line-set.was this replaced also?

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,601
    Not an uncommon complaint with an A/C that has a scroll compressor.

  4. #4
    Join Date
    Jul 2008
    Posts
    11
    Quote Originally Posted by dezerttech View Post
    if sound is not present without cond unit running sound like a possible vibration in line-set.was this replaced also?
    The lines were not replaced, however one thing, I thought lowered the sound just a bit, I removed the line-set holding bracket that secured the line to the floor joist. I thought it was vibrating sound up through the floor. At first it seemed liked the sound deminished a bit, now I'm not too sure. Should I have had my lines replaced? Can 14 year old lines become noisy? I didn't here a peep out of them with my old York A/C unit and evap.
    Last edited by Glenn54; 07-11-2008 at 12:37 PM. Reason: additional info.

  5. #5
    Join Date
    Jul 2008
    Posts
    11
    Quote Originally Posted by BaldLoonie View Post
    Not an uncommon complaint with an A/C that has a scroll compressor.
    Any tricks of the trade to quiet it a bit?

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,601
    Isolate the lineset from the building. You probably did help it manipulating that bracket. Changing lineset wouldn't change things unless they were run differently. Your oldie didn't have a scroll which is why you didn't used to hear it.

  7. #7
    Join Date
    Jul 2008
    Posts
    11
    Quote Originally Posted by BaldLoonie View Post
    Isolate the lineset from the building. You probably did help it manipulating that bracket. Changing lineset wouldn't change things unless they were run differently. Your oldie didn't have a scroll which is why you didn't used to hear it.
    OK, I removed the remaining holding clamps completely decoupling the lineset from my house framing. That reduced the noise a bit. Would wrapping the line in additional padding help any or is this about as good as it's gonna get?

  8. #8
    Join Date
    Jul 2008
    Location
    Alabama
    Posts
    658
    Quote Originally Posted by Glenn54 View Post
    Hello all. Glad to be a new member of the site. I have a 15 year old York furnace, mod#P2MPD14N08001B 115v-1PH-60hz. The York A/C unit was replaced about 3 years ago with a Frigidaire FS5BD and evap coil C3BA-048. At the time the A/C and evap coil were replaced, the tech also removed the blower wheel for cleaning. One thing I've notice since the repacement A/C and evap, is that everytime the A/C cycles on I can hear a low pitched hum resignating up through my bedroom floor as my 8'X8' utillity room is just below. The noise is only present when the A/C is on. With just the fan in "on" or with heat during the winter, I do not hear it. At first, I thought it was sound resinating from the outside unit that's located just below my bedroom window (one story down), but when I place my ear directly to the floor carpet area where the furnace is located just below, the hum can be heard loud and clear. This past weekend, I replaced the 15 year old blower motor and run capacitor thinking it might be showing it's age with noise, but the hum is still present. I thought that I could live with it, but I'm a light sleeper and find the hum somewhat annoying everytime my A/C cycles on, while trying to fall asleep. Any input would be greatly apreciated. Thanks


    Hey Glenn, try this.

    Turn the a/c on. Go outside. Turn the power off to the outside unit.
    Go inside to see if the noise is still there. If it is, there may be duct issues when they changed the coil. If not, the scroll compressor is the answer.
    Vibration limiters could be put on the outdoor unit to make the noise tolerable.

    I did see this once..... we tried everything to quiet a unit down. Turns out that the condenser fan motor was the culprit. Had a bad bearing causing the noise.

  9. #9
    Join Date
    Jun 2008
    Location
    west point, ga.
    Posts
    328
    Back when I was in the gas business we used fiddle sticks.

  10. #10
    Join Date
    Jul 2008
    Location
    Alabama
    Posts
    658
    Quote Originally Posted by RDP View Post
    Back when I was in the gas business we used fiddle sticks.
    WTF is fiddle sticks??

  11. #11
    Join Date
    Jun 2008
    Location
    west point, ga.
    Posts
    328
    Everybody knows what fiddle sticks are.How long have you been in hvac?

  12. #12
    Join Date
    Jul 2008
    Location
    Alabama
    Posts
    658
    Quote Originally Posted by RDP View Post
    Everybody knows what fiddle sticks are.How long have you been in hvac?

    Wise hvac master. Forgive young grasshopper ignorance.

  13. #13
    Join Date
    Jun 2008
    Location
    west point, ga.
    Posts
    328
    All is well my son.Seriously i vote vibration limiters.

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