New House - Wall mounted Air conditioner noise

[bbz404]

Hi guys. 

I have quite a specific air conditioner noise problem. In our new house, there are 4 air conditioning compressors all installed on the same outside wall. They're all inverters from Eminent brand, three 9,000 BTU ones for the bedrooms and one 18,000 BTU one for the living room. 

Now, two of the smaller units make some noise when the compressor is running. However, it appears only when the speed is not maximum and the noise is quite strange. When you're in bed it sounds like a spinning washing machine. Going outside near the compressors you will still hear some vibration noise but it will sound different. 

Other units are fine. 

We've had all of the inside units cleaned already but this didn't help with the noise coming from outside obviously. 

I chose Eminent brand specifically for their low noise as I've experienced them in a hotel we've been staying before the house was completed and they were the quietest units I've ever seen. The hotel ones were regular compressor ones though, not inverters. 

Now I am a bit frustrated as I paid extra to have these Eminent installed (same price as Daikin) and the outside noise is annoying. 

The inside units also make more noise than my Mitsubishi one in Bangkok for instance and this really is a bummer. I am afraid the whole installation is not done properly. 

 

Any ideas on the origins of the outside "washing machine" noise?

[stubuzz]

I think it can only be the compressor or the fan. Is it still under warranty?

[bbz404]

1 minute ago, stubuzz said:

I think it can only be the compressor or the fan. Is it still under warranty?

Sure still under warranty. But that would mean it's a manufacturing problem in your opinion?

[wgdanson]

2 hours ago, bbz404 said:

I am afraid the whole installation is not done properly

Sounds like they did not put any kind of sound insulation, rubber washers, on the bolts holding compressor supports to the wall. My Mitsubishis do have that.

Edited August 24, 2018 by wgdanson

[Moonlover]

I'm sure that your problem is due to 'harmonic resonance'. Even though the compressors run quietly, they do still do produce some noise, which is, of course vibration.

 

That vibration is hitting the 'harmonic frequency' of the wall and causing it to vibrate and the sound is being amplified. It's the same effect that we experience from the sound box of a loudspeaker.

 

The solution is to physically isolate the compressor units from the wall with damping mounts. Have a chat with your installer.

Edited August 24, 2018 by Moonlover

[CGW]

I agree with "Moonlover" its harmonics, not sure if your unit has a "quite outdoor unit" button - Daikin have this? worth a try, may change the harmonics.

Our kitchen hob extractor does similar.

[bbz404]

Sorry just got back to the house and managed to take some photos. Actually I have rubber dampers under the compressors but not on the wall mount. Is there some specific screw to use that dampens the noise going to the wall?

[johng]

maybe  loosen the dampers a bit  or try some different  thicknesses

[Moonlover]

58 minutes ago, bbz404 said:

Sorry just got back to the house and managed to take some photos. Actually I have rubber dampers under the compressors but not on the wall mount. Is there some specific screw to use that dampens the noise going to the wall?

Now that you've posted a photo, it is obvious what the problem is. Your installer has simply put some rubber sponge pads under the unit. That does not isolate the unit from the mounting frame.

 

You need purpose built dampers, sometime known as anti-vibration mounts or antivibs. See Johng's photo.

 

No, the mountings frames are not normally mounted to the wall on these. They only work with the bolts mounted vertically.

 

As I said previously, get the installer back to do a proper job.

 

Good luck.

 

ML

[bbz404]

14 minutes ago, Moonlover said:

Now that you've posted a photo, it is obvious what the problem is. Your installer has simply put some rubber sponge pads under the unit. That does not isolate the unit from the mounting frame.

 

You need purpose built dampers, sometime known as anti-vibration mounts or antivibs. See Johng's photo.

 

No, the mountings frames are not normally mounted to the wall on these. They only work with the bolts mounted vertically.

 

As I said previously, get the installer back to do a proper job.

 

Good luck.

 

ML

I've just had a look around the village and the other wall mounted air con units are as in the attached photo. Only mine use different rubber mats. I will ask the installer back. 

 

Moonlover, what do you mean by "

No, the mountings frames are not normally mounted to the wall on these. They only work with the bolts mounted vertically."? 

[johng]

3 minutes ago, bbz404 said:

Moonlover, what do you mean by "

No, the mountings frames are not normally mounted to the wall on these. They only work with the bolts mounted vertically."? 

The metal frames are not mounted to the walls with anti vibration pads/damper pads.

the aircon compressor units sit on  the metal brackets  but isolated from them via  the damper pads.

they are designed to take compressive force ie mounted vertically   if you use them horizontally  like you would have to between the bracket and wall..then  the whole lot would fall off the wall because the rubber would not support the weight    they are 2 ( supposed to be ) separate  lengths of threaded studding "welded" together by the rubber damper.

[bbz404]

1 minute ago, johng said:

The metal frames are not mounted to the walls with anti vibration pads/damper pads.

the aircon compressor units sit on  the metal brackets  but isolated from them via  the damper pads.

they are designed to take compressive force ie mounted vertically   if you use them horizontally  like you would have to between the bracket and wall..then  the whole lot would fall off the wall because the rubber would not support the weight    they are 2 ( supposed to be ) separate  lengths of threaded studding "welded" together by the rubber damper.

I see so really I just need the correct vertical dampers. Horizontally, it's fine right? 

[johng]

You need the correct damper mounted vertically between the metal bracket and the aircon metal casing

as shown in my photo.

 

it is not normal to have dampers between the wall and the metal brackets.

[Moonlover]

43 minutes ago, bbz404 said:

Moonlover, what do you mean by "

No, the mountings frames are not normally mounted to the wall on these. They only work with the bolts mounted vertically."? 

Yes correct. The mounting frame should be solidly attached to the wall as yours appear to be.

 

The unit, once mounted properly on dampers then 'floats' on the rubber mounts and is mechanically isolated from the frame itself. A motor vehicle engine is mounted in a similar way, for the same reason.

 

I'm your problem will be resolved if you follow mine and Johng's advice.

 

Good luck.

 

ML

[sometimewoodworker]

4 hours ago, Moonlover said:

No, the mountings frames are not normally mounted to the wall on these. They only work with the bolts mounted vertically.

 

3 hours ago, johng said:

it is not normal to have dampers between the wall and the metal brackets.

Possibly a miscommunication, bbz404 wall mounts are correctly mounted to the wall (no dampers)

 

but the rubber dampers are too thin and quite possibly the bolts are too tight, it could also be that the outside units are just noisy and have poorly balanced fans.

[Moonlover]

I do hope that we haven't had loads of TVF members rushing out to look at their A/Cs units and thinking 'there are no damping mounts, it's been installed wrong'.

 

Don't worry. Not all installations need them. It all goes back to what I mentioned before, harmonic resonance between wall and unit.

 

Our bedroom unit does not have any either, but because it's mounted close to the concrete support post the wall is less likely to vibrate. And in fact it runs completely silently.

 

So no need to panic.

[bbz404]

any idea where I can purchase the correct dampers? HomePro? Or any Air-Con supply shop?

Installer is not available now so I would like to try on one of the aircons myself. Shouldn't be too hard of a job.

 

Thanks

[bbz404]

Moonlover, very good advice as in rental house in Bangkok we have a Mitsubishi outside compressor unit maybe 1.5 metres from our heads when we sleep and we cannot hear anything. And I confirm they also have just small rubber mats. It is however mounted near a concrete column as you say. Also it's not an inverter so the speed of it is always the same, either on or off only.