unusual request

[raymo]

Anyone here with extensive knowledge of reverse cycle a/c units?
My Fujitsu 7kw unit most of the time makes a sort of low whistling noise
which is cyclic, whistles for about 2 secs, becomes much lower volume for about 2secs, and then returns to its original volume; repeats this
ad infinitum. It is not loud; just audible enough to drive me insane.
As far as I know there are no oscillating parts in an a/c, [ the vane swing feature is disabled] ,and altering the fan speed doesn't affect the noise.
All suggestions or comments welcome.
raymo

[glend (Glen)]

I imagine that the compressor would be an oscillating component.

[sheeny (Al)]

Sounds like "beating" - two frequencies close together - the frequency of the beat is the difference in frequencies of the two original frequencies. This is the basis of tuning a musical instrument.


2s period corresponds to a 0.5Hz difference between say the compressor motor and the fan motor (or whatever the sources are).


Al.

[iborg (Philip)]

Hi


I am assuming you have a smart phone. Download and install an app such as Physics Toolbox.


It has various items listed under Acoustics. I suspect the Spectrum Analyzer or Tone Detector would be helpful to identify a situation such as Al has suggested.


Philip

[raymo]

Thanks for the responses, much appreciated.
Glen, the compressor is in the outdoor part of the a/c, and the noise is definitely coming from the indoor unit.
raymo

[JA]

Hi Ray,

If it is indeed whistling as opposed to a squeak or scrape, then it's more suggestive of problem related to air moving through or past an orifice or tight, possibly varying gap, BUT you mentioned the whistling doesn't change with fan speed which is not what I would have expected.

In any event I would do a few things to investigate ...
1. Remove the filter and inspect it for any damage or loose adhered debris.
2. Run the unit without the filter to determine if the whistling changes in any way.
3. Carefully examine with torch in side of the indoor unit looking for any loose components it debris.
4. Lastly, if you're game, remove the indoor unit cover (not always easy) and examine for loose components, debris or any mechanism with excess play.

Good luck on the hunt.

Best
JA

[raymo]

Thanks for the suggestions JA. The only thing that I haven't done is remove
the cover, because I am no longer stable on a ladder without holding on to
something. Getting old sucks. Looks like I'll have to bite the bullet and get
it professionally looked at.
Incidentally, I think you are right about the cause,
because as far as I know there are no moving parts inside the unit, apart from the fan
and the vane swing feature which is turned off. I discovered that the whistle doesn't
actually stop between pulses; it just becomes almost inaudible.
raymo

[peter_4059 (Peter)]

Maybe it is the refrigerant passing through the indoor unit. Try running it in fan only mode and see if you can still hear the noise.

[JA]

A clever suggestion from Peter (Hello Peter). Building further on that: try it it both heating and cooling modes.

Best
JA

[raymo]

Thanks for the latest suggestions. The noise remains the same whether set
on heating, cooling, or fan only, including the period when the unit is
quiescent when changing from one mode to another.
raymo

[Nikolas (Nik)]

Give it an almighty whack and see if that solves it

[iborg (Philip)]

One should never give something an almighty whack - one should simply employ percussive maintenance!

[raymo]

raymo

[Nikolas (Nik)]

Like this?

[Boozlefoot]

Selenocosmia crassipes. (Need to remove the cover to locate)

https://www.inaturalist.org/taxa/779...smia-crassipes

Also best fixed with a hammer.

[iborg (Philip)]

Hi


The app I mentioned also includes a sound meter, by moving the phone slowly around the unit, it may help pinpoint where the noise is coming from.


Philip

[raymo]

Sorry, I don't have any mobile phone, let alone a smart one. Don't have a smart tv either, not that that is relevant.
raymo

[iborg (Philip)]

I suspect a smart choice.