# Fujitsu mini split outdoor unit makes excessive noise



## mhylmz (Nov 27, 2015)

We have installed a Fujitsu AOU48RLXFZ1 outdoor unit on the exterior wall of our house. There are 6 indoor units connected to this outdoor unit. This is in San Francisco Bay Area. 

When the outdoor unit is running, it creates a significant amount of vibration and noise. Although there are vibration dampening neoprene pads under the feet (between unit feet and wall bracket), it still vibrates the whole wall when it runs on high. It is also very loud behind it. I measured about 72dB at low frequencies (~125Hz) at about 3 feet distance from the back of the unit. The compressor seems to be source of all vibration. The fan is very quiet. Condenser seems to have a high level of low frequency noise. The mix of vibration and low frequency noise is very irritating. I can hear the noise behind 3 walls in the next room.

The first question is whether this is normal. The outdoor unit is mounted on wall brackets and the space between the back of the outdoor unit and the wall is about 12 in. 

When I checked the compressor inside the unit, I saw that the compressor is sitting on rubber isolation feet. However, the bolts are not tightened to press the compressor to the rubber feet. There is a 3/8-in gap between the nut/washer and the compressor feet (which sits on rubber isolation feet). Does it need to be tightened?

Another observation: The rubber feet under the compressor seems to dampen the vibration that travels through the compressor feet. However, anything that touches compressor body vibrates a lot. And the whole outdoor unit vibrates with it, includes electrical wires and copper lineset connected to the outdoor unit.


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## oldognewtrick (Nov 28, 2015)

How old is the unit and who did the install? Is something new or has this been an issue since day one?


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## mhylmz (Nov 29, 2015)

I did the install recently. This is a brand new system. And it works fine except the noise part. The issue was immediately apparent upon turning on all indoor air handler to max heating capacity.


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## mhylmz (Nov 30, 2015)

Here are some pics of how the compressor legs are bolted. You can see the gap between the metal washer and black compressor leg sitting on rubber legs. There is a rubber washer between the metal washer and the compressor leg, but it is not pressed. I tried to press the nut down, but it does not turn any more. So, either it was designed like that, or we are missing some sort of thicker rubber washer between the washer and the compressor leg.


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## nealtw (Nov 30, 2015)

I went looking at the installation manual, they do say something about more noise if hung on a wall and the talk about more cushoning when sitting on concrete. and then I found on pg 36 that the y have something called low noise mode which takes away from performance. Good luck


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## nealtw (Nov 30, 2015)

[ame]https://www.youtube.com/watch?v=6TsvZqOFHyw[/ame]


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## buffalo (Nov 30, 2015)

I had a Fujitsu and it was pretty quiet. How solid is the wall? Mine was a single 2 ton minisplit s so yours sounds like a much larger unit.


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## mhylmz (Nov 30, 2015)

The wall is a 2x4 16" OC stud wall with no insulation. Siding is 7/8" stucco. I opened up the walls in that room to add insulation. I will also add some noise reduction assembly (green glue with 2 layers of drywall). I hope it will help. The noise is pretty low when only a few indoor units are running. The problem starts at around max load. I also tried "low noise mode", it helped a little, but not much. Vibration seems to be the main problem.

I will move the unit from the wall if nothing else helps. And also add noise deadening boards behind it.


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## mhylmz (Dec 1, 2015)

Here is an official response from Fujitsu, for anyone having a similar problem: "If wall brackets are on a frame wall, noise from outdoor unit can be amplified. If sufficient vibration dampeners do not help the situation, the only recourse may be to move unit off wall brackets and mount on heat pump risers on the ground. The nut on the compressor mounts can only be tightened so far there are spacers that limit how far it can be tightened."


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## nealtw (Dec 1, 2015)

They are just full of help.


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## frodo (Dec 3, 2015)

.....................


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## WyrTwister (Dec 3, 2015)

Mount it on the ground & get rid of the wall brackets .

     The 2 I installed ( with help from family ) are mounted on a concrete slab and on 12" x 12" x 3" " paving stones " .

     You installed the unit .  So it did not quite work out .  Experience is what you got when you did not get what you wanted .

     Correct it and be happy .

God bless
Wyr

PS  How high are you off the ground ?  How securely are the brackets mounted to the wall ?  Do you have any vibration isolators between the brackets and the outside sheet metal housing of the condenser unit .

     I think you probably need some looseness in the compressor isolators , to allow the compressor to move a little ?


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## frodo (Dec 4, 2015)

always been my experience to remove the bolts hold the condenser, not lock it down.

think about it.  if you cause it to become ridgid to the frame,  when it shakes it will transfer he shake to the cabinet

if it is loose, when it shakes, the rubr will absorb the movement.

matter of fact..all compressors usually have a tag that says remove shipping bolt before install


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## mhylmz (Dec 4, 2015)

WyrTwister: 
The unit is 2 ft off the ground. Brackets are custom made from 1.5" steel square tube, 2" steel channel, and 2" angle irons (all 1/8" thick) and secured to wall very well. The bracket can carry four of these units without any problem, probably wall will give up before the bracket 

The reason for custom made bracket is the fact that Fujitsu manual required min 12" clearance on the back side. I could not find a ready bracket that can hold 220 lbs and give 12" clearance on back. There are vibration dampening pads under the feet of the unit, so units does not directly touch the bracket. 

frodo: Yes, I agree with your assessment. In fact, there is very little vibration next to the pads that the compressors sit on. The problem is, they made the unit very tight and lot of stuff touches the compressor inside the unit. So, when the compressor start vibrating, it is transferred to copper tubes and wires etc. 

May be the most interesting part is that the actual bracket does not vibrate much. Most of vibration seems to be transferred to the wall through the liquid-tight conduit  I got some sorbothane vibration dampeners. I will add those in all contact points and see how it does. 

Another option is to create a steel platform off the wall and keep the unit where it is now. That is relatively easy to test by adding temporary supports from bottom and disconnecting the unit from brackets. If it does not help either, I will just move the unit on a concrete pad. That will require some new copper tubes etc.


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## nealtw (Dec 4, 2015)

Build a table to bolt to the concrete below and leave it where it is but not bolted to the wall.


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## WyrTwister (Dec 5, 2015)

nealtw said:


> Build a table to bolt to the concrete below and leave it where it is but not bolted to the wall.



     That is what I would do , also .

     Or use concrete blocks under it , stacked to match the bottom of your frame .  Would be better if they were filled with concrete and a little rebar .  The interior of thus formed rectangle of concrete blocks could be filled with dirt .

     All in all , looks like you did a pretty good job with the install .  This one point just snuck up on you and bit you a little .

     If all your refrigeration lines are leak free & all the units are performing OK , I would not mess with them .

God bless
Wyr


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## BASguy (Dec 5, 2015)

nealtw said:


> Build a table to bolt to the concrete below and leave it where it is but not bolted to the wall.




+2 A buddy of mine had a similar problem with his install and we built a nice wood platform and moved it off the wall about 6 inches.  Worked great.


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## frodo (Dec 6, 2015)

mhylmz said:


> WyrTwister:
> 
> Most of vibration seems to be transferred to the wall through the liquid-tight conduit
> 
> I got some sorbothane vibration dampeners. I will add those in all contact points and see how it does.




is the conduit you have the line set in, touching the unit?

if so.

remove the conduit [looks to be sheet metal] from the unit.
leave a 1'' gap between unit and conduit.
seal the gap with childers [pooky]  

Mastic:  Whenever edges or cuts of fiberglass are exposed, we seal the fiberglass with CP-11 or CP-10 Vi-Cryl white mastic.  This mastic is a fibrous based paint which will seal the fiberglass from water.  Mastic can also be used to paint the ASJ jacket of Fiberglass Pipe Insulation to protect the jacketing from weather (great for use in exposed crawlspaces).  Tip: CP-11 is brush grade (most popular), CP-10 is trowel grade.

if the conduit is causing the problem,  this will isolate and weather seal the gap.


as far as stuff touching the compressor,  open the unit,  bend the crap out of the way.  use zip ties if you have to.

it appears to me, the unit is vibration isolated, but the piping is not

or rather the conduit for the pipe


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## WyrTwister (Dec 6, 2015)

Never thought about it before .  

     Non - Metallic Liquid Tight might be a little better than Liquid Tight with the spiral metal core ?

God bless 
Wyr


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## WyrTwister (Dec 7, 2015)

frodo said:


> always been my experience to remove the bolts hold the condenser, not lock it down.
> 
> think about it.  if you cause it to become ridgid to the frame,  when it shakes it will transfer he shake to the cabinet
> 
> ...



     I agree , try loosening the bolts , instead of tightening them down .

God bless
Wyr


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## frodo (Dec 7, 2015)

WyrTwister said:


> Never thought about it before .
> 
> Non - Metallic Liquid Tight might be a little better than Liquid Tight with the spiral metal core ?
> 
> ...




you do not want any metal, bridging the unit to the conduit

i do not know liquid tite

i know childers cp-11

we use it on commercial jobs


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## mhylmz (Dec 8, 2015)

With "conduit", I meant the electrical liquid-tight metallic one.  It is attached to unit as expected.

The lineset cover is PVC, it does not directly touch the unit. There is a 12" gap, but the lineset is wrapped inside another PVC tape between the lineset cover and the unit, and it touches the unit. I will use the mastic as recommended.

Thanks for the great tip everyone. I will work on the table idea soon.


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## Bill_Christian (Aug 19, 2021)

mhylmz said:


> We have installed a Fujitsu AOU48RLXFZ1 outdoor unit on the exterior wall of our house. There are 6 indoor units connected to this outdoor unit. This is in San Francisco Bay Area.
> 
> When the outdoor unit is running, it creates a significant amount of vibration and noise. Although there are vibration dampening neoprene pads under the feet (between unit feet and wall bracket), it still vibrates the whole wall when it runs on high. It is also very loud behind it. I measured about 72dB at low frequencies (~125Hz) at about 3 feet distance from the back of the unit. The compressor seems to be source of all vibration. The fan is very quiet. Condenser seems to have a high level of low frequency noise. The mix of vibration and low frequency noise is very irritating. I can hear the noise behind 3 walls in the next room.
> 
> ...


This is a long shot but could be an easy fix. If compressor vibrates at same frequency as wall, or a multiple (twice, triple, half, a third) or fraction (2 to 3, 2 to 5...) it can get REALLY loud. If it's a variable speed compressor (most new ones ARE), can you limit it to not hit the magic number? (Watch the video of the Tacoma Narrows Bridge to see what matching frequencies can do.) I have see this with a big rooftop unit, when supply fan hits magic speed the whole roof goes "live".


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