Fujitsu mini split outdoor unit makes excessive noise

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frodo

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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

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

2015-12-07_0436  snap shot.jpg
 

mhylmz

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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.
 

Bill_Christian

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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.
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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