This is a thread I was hoping Number Twelve would answer but anyone is welcome to chime in.

I have a fairly loud AC unit sitting next to my house. It is now 10 years old and has been about equally loud since my neighbor build his house next door. Before the house was built, there was nothing to reflect the sound so i don't remember how loud it was before the house was built. The original owner was a cranky old man like myself and he never went outside so i was never concerned.

Last year, a new family moved into the house next door and they have little kids and play in the yard next to my AC unit. It has to be loud for them and I am a bit embarrassed. Is there any advice how to quiet the compressor/fan unit? I am not sure how loud/quiet it should be but any advice is appreciated.

 

Is it the compressor that is loud or the fan that is loud?

Either one could be as simple as having a rubber vibration isolator bushing that is bad.

Some years ago I was given a good dehumidifier that had that problem because one rubber bushing that held up the compressor had fallen apart.
The previous owner had it in his basement and could not stand it because it could be heard on the second floor when it cycled on.

A piece of rubber hose and a larger bolt and it was good to go and very quiet too!

 

You have the right idea about the building being a sound reflector. Think of something that would wreck its ability to bounce sound, or add bushes at least a foot taller than the condensing unit, or build a wooden fence at least 18 inches away from the condensor and 2ft to 3ft higher. You usually don't have to close it in on all sides.

Don't create the sound, or don't bounce it, or absorb it, or re-direct it. That's all you can do.

ps, I didn't copy tcmtech because 1) he's right, 2) they usually don't fail that way at 10 years old, and 3) you said it was probably that way since birth.
It's usually just bad design, like a 15 inch fan blade at 3450 RPM instead of an 18 inch fan blade at 1750 RPM, and there's not much you can do about that unless you're good with sheet metal and want to redesign the fan section.

Oh yeah, the sound standard is something like 78 db at 15 feet, but I don't remember because it's up to the manufacturer to obey that law. The only thing I can get searching the internet is 45 db, A weighted, at the property line. Not the right number for your job.

 

The fence/sound wall was my next option. i was hoping some company was widely known for designing quiet fan blades (air foils instead of big pieces of sheet metal) or something I could do with my compressor.

I think my compressor outside is way oversized for the A-coil in side. I was wondering if that was causing some of my problem (I forgot to mention that the first time). I have no proof but the size of the big loud RUUD unit just seems odd compared to the neighbors' units.

 

I fitted mine with four rubber vibration mounts from an army surplus outfit, they resemble the automotive motor mounts, just a bit smaller.
Max.

 

I think my compressor outside is way oversized for the A-coil in side.

Not possible. If the compressor is too big the A coil will freeze.

So...describe the sound. Do you get a big BA-OOOoo when it starts? That's the compressor. Bearing noise? That can only be ball bearings. The bushings don't get noisy, they just seize up. Fan turbulence? Bad design. Rattles? Fix 'em yourself. etc.

You can get a blanket for the compressor, or make one. (The compressor steals most of its cooling from the Freon flow.)
You could change the design to a squirrel cage fan, but, again, you're into sheet metal work and some math you better be right about!

 

I was just out to answer your question. The sound is a combination of fan turbulence (not annoying), compressor noise (like a commercial air compressor), and what I now realize is a bunch of sheet metal flexing and vibrating.

I think some of the rubber mounting ideas may help.

My compressor unit sits on two metal shelf brackets they are attached to the house. Since these have RUUD labels on them, I assume they are designed for this purpose. The brackets are sized for the 2x4 stringers connecting the two brackets to make the shelf.

I will take the unit apart and put some Epdm gasket in material along all seams to stop the metal-to-metal noise and put some rubber jounce bumpers under each foot.

 

Sounds like a plan.

Let us know how it turns out.

 

It's a rare machine that I can't fix the rattles by replacing missing screws or tightening the screws it still has. Sometimes a tiny pre-bending of the wire shield or a piece of sheet metal so it is under tension or compression after it's screwed down.

Of course, I carry over sized screws by the hundreds. The sheet metal is so thin that the holes get stripped out regularly. That's one good reason why you shouldn't oil the motor bushings every year if they are still flooded with last years' oil. Oil it now and write the date on the machine, then come back in 2 years or 3 years and check again.