North Carolina Compressor "hum" noise in ducts

Discussion in 'Maintenance and Troubleshooting' started by martyg, Dec 1, 2014.

  1. martyg

    martyg New Member

    I have a "package" unit installed (horizontally) in my crawl space. While very little noise can be herd from the air handler I get a compressor hum through some of my floor registers. The compressor is wrapped with a sound blanket. and my duct system runs from a ridgid plenum to a flex duct that connects it to a ridgid trunk line and then to flex duct up to the boots.
    Most of the noise comes from the boots at the end of the trunk line. The interior of the plenum and trunk line are lined with insulation.
    Does anyone have an idea of how I can damp down the noise?
  2. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Is the unit suspended from the floor or resting on the ground?
  3. martyg

    martyg New Member

    The air handler is sitting on blocks (on the crawl space floor) with a 1" thick neoprene pad between the cabinet and the block. However; the ridged truck line is hung from the floor joists on s cleats. I have been thinking that the flex duct between the plenum and the trunk would eliminate any direct vibration and assumed the noise was air borne. Still it's worth a try; I will rehang the trunk with nylon strapping and see if that helps.
  4. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    A canvas connector could help.

  5. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    It would be good to determine whether the problem is noise vs vibration. Granted all noise originates from vibration, but what I'm getting at is whether the compressor noise itself is moving through the duct system or whether some sort of harmonic or resonance is moving through the structures near the system.
  6. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Heating code uses the term "vibration isolation" or as Mark called it a canvass connector. This helps prevent telegraphing noise.
  7. martyg

    martyg New Member

  8. martyg

    martyg New Member

    I agree and am 100% sure it is the compressor noise traveling ( and being propelled by the fan) through the ducts. the compressor was loud from the minute it was installed, hardly the "virtually silent" Climate Master claims in their advertising.
    While in the crawl space all of the noise is emanating from the compressor side of the air handler and 10' away from it there is almost no noise. There is no noise from the ridged trunk line, unless you put your ear next to it.
    I'm still considering a canvas connector as it would place an additional break between the air handler and the ridged ducts but I feel like the noise is mostly air bound.
    I did re-hang that ridged trunk line with nylon strapping and removed the metal hangers. I maybe got a slight reduction in noise, but not much.

    Then I tried a new approach; I believe the compressor is transferring it's noise to the air handler cabinet which in turn is acting like a drum and broadcasting the noise. I remounted the air handler on spring loaded vibration isolators ( with cork and neoprene pads) and I would guess that I have a 50% or greater reduction in noise through the ducts! I'm also thinking that the noise traveling through the trunk is hitting the end cap and then just moving up through the flex runs at the end of the line so I'm going to add 6' of 8" flex to the end cap and just cap it off. Hoping that the noise will move past the last couple of runs and die in the new flex.
  9. geoxne

    geoxne Active Member Forum Leader

    Check to see if the compressor shipping brackets have been removed.
  10. martyg

    martyg New Member

    Thank you! I backed off the hold down bolts and the noise from the compressor was reduced by half again. I'm now at an acceptable level; there is still a little hum that you don't notice until the unit shuts off and it is completely quite.
    I checked the unit in my office and while it was not very loud loosening the hold down blots reduced the noise level there as well.
  11. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Take them all the way out and see what happens. Unless you are taking the machines on a road trip, they will not go anywhere.

  12. ACES-Energy

    ACES-Energy Member Industry Professional Forum Leader

    have you had the unit vitals checked out? I have seen noise issues with contaminated refrigerant, too much/not enough source water flow, air flow, should also look to see how the unit is operating..
  13. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    You generally want the entire underside of the cabinet supported or the compressor can ring the bottom like a drum.
  14. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Back in the day, I had a Lenox Pulse ring backing pans in a kitchen 60 feet away.
  15. martyg

    martyg New Member

    I installed two canvas connectors, one between the air handler and and the plenum and one between the 18" supply flex and the transition to the supply trunk line. And that did further reduce the noise in the house.
    While admiring my work I noticed a bit of hum from the pump pack that I was unable to hear before. The pump pack was mounted to a plywood panel that is attached to the foundation wall and it had neoprene&cork isolators between the plywood and the pump pack baker plate. I suspended the pump pack from the ceiling with a nylon zip tie and removed the lag screws securing the pump. This also helped.
    I was now at a point where I had eliminated about 80% of the offending noise and certainly at an acceptable level but I did still have a slight hum on one side of the house and it still seamed to me coming from the floor registers.
    While I was re-hanging the pump pack I notice quite a bit of vibration in the loop pipes so I returned to the dungeon and took a closer look at the loop pipes. My pipes enter the foundation at the center of the rear foundation wall and run at an angle to the side foundation wall near the front of the house, approximately a 30' run. The pipes were strapped securly to the bottom of the floor joists in four or five places and in full contact with three supply ducts and one retrurn air duct on the side of the house where the noise was coning from. I rehung the pipes so there is no longer any contact with the floor joists or ducts and the THE NOISE IS GONE!
  16. Ed Spicer

    Ed Spicer New Member

    Hello martyg, I am having vibration and noise issues as well. I was interested in your comment above about suspending the pump pack from the ceiling with a nylon zip tie. My pump is screwed into one of the concrete footers and the pump vibrates the footer and the floor joists above it. So, what did you connect your zip ties to and how? They must have been pretty strong zip ties. Appreciate all the information I read above and hopefully this will help as well. The noise is annoying me very much. I posted a photo of what I just described. Thanks

    Attached Files:

  17. Excellent comments ! The noise problem would be exacerbated by vibration of motor/compressor or fan blower. On brand new equipment, that usually is NOT the problem. As earlier noted, the rubber mounts on the compressor will not do what they are designed to do if the INSTALLER never loosened them from the factory shipping position. I know from commercial that more than one vibration isolator can SOMETIMES be necessary. Sound energy is reduced with the square of distance. Also remember that typical household ductwork insulated on the outside does not abate noise, much. Commercial grade ductwork insulated on the INSIDE does.

Share This Page