reducing rooftop AC vibration

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  #1  
Old 02-05-18, 11:51 AM
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reducing rooftop AC vibration

So my neighbor put a new unit in and it's vibrating and driving us crazy (we're on the top floor; he's below us). It's a ThermalZone unit. He's had various AC people come in and try to get it to stop vibrating through our apartment but we're not having too much luck. The last AC guy said he thinks the problem is the AC stand is placed on support planks, and if the unit was moved to an area of the roof (like over the living room) with a little more give it would probably be better.

So 3 separate questions:

1. Does that sound like something we should try? It's 180 lb unit and I'm worried without support it could fall through at some point. It's a 60-year building that doesn't really have the best construction.

2. Before we do something that drastic I was thinking of rigging together a platform underneath the unit (23 inch clearance) with a rubber or vibration pad top that pushes up against the unit to see if distributing the weight more makes it any better.

Does this sound like a particularly crazy plan? It wouldn't carry the whole weight, just push up enough to carry some of it. If it sounds like something that might work, does anyone know of a way to make sure it pushes up enough? The unit is bolted to the stand so there's no way to lift the unit up and place it on the platform. I was thinking of using some sort of jack, but I don't think jacks are meant to lift things permanently. Are there any kinds of extendable legs that act as a jack in that way?

3. Would heavily insulating my ceiling possibly fix this? I don't mind getting that done on my own expense because it will also help with keeping the place cool (this is in South Florida), but I don't want to do it unless it helps with the vibrations, too.
 
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Old 02-05-18, 01:28 PM
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It's possible that the AC unit is just hitting the resonant frequency of that part of the roof. Moving the unit even just a few feet might be enough to prevent it from resonating and cut the apparent vibration dramatically. Generally I'd try to move it closer to the edge of the roof or to a load bearing wall underneath the roof.
 
  #3  
Old 02-05-18, 04:03 PM
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Originally Posted by Pilot Dane View Post
It's possible that the AC unit is just hitting the resonant frequency of that part of the roof. Moving the unit even just a few feet might be enough to prevent it from resonating and cut the apparent vibration dramatically. Generally I'd try to move it closer to the edge of the roof or to a load bearing wall underneath the roof.
Thank you for the advice!
 
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Old 02-05-18, 04:13 PM
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If that is the outside unit of a split system..... it's going to be connected with refrigerant lines and power. There isn't going to be too much movement available with that tether.
 
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Old 02-08-18, 04:42 AM
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Is it blower noise? or is it the refrigeration lines that are vibrating, is it noisey with only the blower running? Is it vibrating badly on the roof?
Geo
 
  #6  
Old 02-10-18, 11:19 AM
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Vibrating outdoor unit

Since this outdoor unit is on the roof if maybe fixed to the roof so high winds will not blow it off or cause damage to the refrigeration lines, you may insert rubber pads between the unit and the surface it comes in contact with and then re-secure the unit to what it was secured with just not to firmly also loosen the bolts on the compressor just a tad, and finally make sure the fan blade is not bent. That sucker turns roughly at 1075 rpm's so it to can vibrate. Moving the unit will be costly and without any guarantee that it will help your situation. Good luck!
 
  #7  
Old 02-15-18, 10:00 AM
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thank you everyone!

Thank you everyone! I think you all are pretty much right with everything you say. I'm worried about moving the unit because there aren't really supporting walls under the roof where I would have to move it to not hear it. The last AC guy bolted it down better and put a lot more vibration pad support and it's gotten a little better.

So my last question is this:

I'm trying doing something a little jury rigged before I consider expensive options. I bought a cheap $5 IKEA metal and plastic stool (weight capacity 220 lbs), put plywood under the unit, then had the stand legs be on 4 vibration pads on top of the plywood, with 4 large (6"x6" vibration pads) stacked between the stool and the bottom of the unit. Picture is attached.

It actually seems to help! The unit is definitely quieter when you're standing next to it. The bedroom hasn't improved too much but the rest of the house has. I'm kind of shocked because I am not the handiest guy.

My question for the experts on this forum is now:

Does anybody see any drawbacks with this? It's jammed in tight enough so it's supporting some of the unit weight and should not be moved by the wind. If a hurricane's coming I'll have to go up and take it in temporarily, but fortunately that's something that happens on average once every few months (and if I forget, it's like $20 worth of materials).

But can the unit be pushed up like that? Anything I'm not thinking of that could be a problem down the road? Any modifications that you think would make it work better? I'll probably reposition it to try and make the bedroom quieter.
 
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Old 03-08-18, 08:48 AM
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level

make sure the unit is level. most people miss this
 
  #9  
Old 03-25-18, 05:03 AM
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I would try adding concrete garden blocks to the unit to change the mass. Vibration frequency is related to two things, mass and stiffness. You can change the stiffness a little bit in your case but you could also change the mass a great deal. Buy some concrete curb blocks and put them in the mix with rubber floormat or something similar underneath. I had a fan doing the same thing. Fixed it with stepping stones.
 
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