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Old 10-02-2012, 06:17 PM   #1
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Rooftop unit Trane XL14C compressor vibration


Hi

browsed the HVAC forum but could not find an answer. I have a rooftop unit that was installed by some hacks I have since hired a reputable company to fix all their errors but one persists:

The rooftop curb is a solid piece of metal sitting on the pitched roof, and the lip that the unit rests on is too narrow to hold rubber isolators. Because of the metal to metal contact, I have a low frequency vibration that is felt rather than heard in some of the rooms, and the main source is the compressor.

My question is that would additional rubber isolators under the compressor help since I cannot put any between the bottom of the unit and the curb lip?

Would strengthening the roof joists with 2X4 sections tying them together decrease the roof vibration ?

anybody has any advice ?

thanks!


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Old 10-02-2012, 09:03 PM   #2
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Rooftop unit Trane XL14C compressor vibration


Additional weather stripping between the unit and curb may help. Doubt additional rubber under the compressor will help any.

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Old 10-02-2012, 09:09 PM   #3
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Rooftop unit Trane XL14C compressor vibration


check the compressoritself,might need to be floated on the rubber feet that are bolted down during shipping..take a needle nose pliers and pull the tubes out reinstall the bolt and washer socket down till the washer isn't turning with your finger...eye ball the round bottom of the compressor should not be touching the condenser base...check the fan section also it should float a bit making sure they removed the shipping lock down stuff..any thing in a rooftop that spins or turns has to float
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Old 10-02-2012, 09:19 PM   #4
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Rooftop unit Trane XL14C compressor vibration


see if you can find strips of high density neoprene instead of weatherstripping..but only if the weather stripping doesn\t work..I'm afraid it might get chewed up or deteriorate too quickly.

Also, the vibration can usually be further dampened by spring isolators but not sure if you can apply to your mountings
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Old 10-02-2012, 11:56 PM   #5
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Rooftop unit Trane XL14C compressor vibration


knowing that they were hacks, I will check and make sure that everything is "floating" like you said. I will see if I get the new guys to put some neoprene under the unit. Thanks for the info, guys, much appreciated!
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Old 10-03-2012, 08:51 AM   #6
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Rooftop unit Trane XL14C compressor vibration


even the compressor discharge line(super hot line) that travels from the compressor to the top of the condenser within the unit exposed coil area...can give off vibes...had a commercial rooftop 40 ton unit went down 4 floors on the steel within the wall.put my ear up to the wall in a conference room and heard a song goin' on...went up on the roof slid a crow bar under the hot line there and lifted it off the metal base.might not be the unit to the curb.could be the curb to the roof hitting a beam
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Old 10-03-2012, 10:58 AM   #7
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Rooftop unit Trane XL14C compressor vibration


Quote:
Originally Posted by joeyl View Post
knowing that they were hacks, I will check and make sure that everything is "floating" like you said. I will see if I get the new guys to put some neoprene under the unit. Thanks for the info, guys, much appreciated!
And to add to Biggles comment. Have a helper stay in the room where the vibration is heard while someone (you) tweeks the lines, the compressor, etc. to see if the vibration can be lessened. Is the fan unit a consideration for the vibration?
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Old 10-03-2012, 11:04 AM   #8
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Rooftop unit Trane XL14C compressor vibration


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And to add to Biggles comment. Have a helper stay in the room where the vibration is heard while someone (you) tweeks the lines, the compressor, etc. to see if the vibration can be lessened. Is the fan unit a consideration for the vibration?
no the fan unit is not even on when the cooling cycle starts and I can feel the pulsing from the very beginning of the cycle, so it really has to do with the compressor and the refrigerant lines. The techs that came out also made sure that the unit was level, which it was.
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Old 10-03-2012, 11:20 AM   #9
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Rooftop unit Trane XL14C compressor vibration


I have gone through this with a boiler system over offices...$20,000 later installing spring vibration isolators..big improvement but not completely solved. How about using a sky hook..lol...sorry...
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Old 10-03-2012, 11:38 AM   #10
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Rooftop unit Trane XL14C compressor vibration


my tech emailed me back and here is his suggestion:

Right now we are trying to isolate the unit so it doesn't transfer into the house. my suggestion would involve isolating the compressor from the unit by installing vibration absorbers in the refrigerant piping. This would reduce the energy that is being transfer into the unit thereby reducing vibrations in the house.


That sounds pretty close to what Mr Biggles suggested.
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Old 10-03-2012, 04:25 PM   #11
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Rooftop unit Trane XL14C compressor vibration


i would stay away from the vibration elimination off the refriferation lines not going to solve the problem...or you help your wallet put a screw driver tip on the discharge pipe and your ear up to the handle it's not coming from there. what brand and model is the unit..any chance for a pix of the unit on that curbed roof..this may be a try but some automotive type hose cut to 4" pieces...pinch up the unit off the curb and slide a piece in each corner ..just to see if the noise changes.seeing this rooftop the curbing it was placed on has no isolation or elimination on the curbing.. it is all within the Trane unit from the factory fan and compressors....bet its the unit to curb...

Last edited by biggles; 10-03-2012 at 04:41 PM.
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Old 10-03-2012, 04:49 PM   #12
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Rooftop unit Trane XL14C compressor vibration


The model is 4YCY4048B1096AA. I will try to take a pic either tonight or tomorrow.

thanks for the suggestions!
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Old 10-10-2012, 12:20 AM   #13
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Rooftop unit Trane XL14C compressor vibration


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I don't think much can be done with the compressor mounts, they are floating as is.

However I can press my hand on the side of the curb and the vibrations get less intense. Could it be the curb being a loudspeaker?
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Old 10-10-2012, 07:45 AM   #14
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Rooftop unit Trane XL14C compressor vibration


did you happen to take a nut off the compressor foot to see if the metal tube sleeve is out or still there....i would remout that discharge sensoer get the tension off that wire going under that suction line..and wire tie all those wires together...if the harmonics is changing with the touching of the curb it is the unit to the curb...nice install clean.... could of been missing a rubber gasketing before the rig....
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Old 10-10-2012, 11:05 AM   #15
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Rooftop unit Trane XL14C compressor vibration


yes I took the nut completely off, and there was no sleeve there.
The techs came by last week and put 10 of these little 1/4" thick square pads between the curb lip and the unit. Result: not much change

His other idea is that maybe the previous company cut too much of the roof (they did not cut 2 small holes for the return or supply but instead cut a huge hole the size of the curb , and there is too much flex in the area now. Maybe I should be reinforcing the roof slats/trusses from the underside????

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