How To: Quieting a Norcold Refrigerator

[BrianW]

As some have noted over the years, the Norcold fridge that SMB often installs can be prone to noisy operation. I had one in my 1998 SMB and it was pretty quiet and was still running strong 22 years later when I sold the van. My 2011 has basically the same fridge, which works fine but was pretty loud at night between rattles and vibration, so much so that it sometimes woke me up. I finally had some time this fall to try and figure out a solution. So far the easy mods I made have made a huge difference. Rattles are gone, and vibration is much better. Here’s what I did:
Here’s what the back of the fridge looks like. The compressor (vertical cylinder thing) is mounted directly to the metal body of the fridge. The cooling coils mount to the bracket that holds the compressor to the body. And there’s a small cooling fan mounted at the bottom. The noise begins when the compressor kicks on, creating a sort of harmonic vibration that creates rattles and transfers to the van through the refrigerator cabinet wood.

I figured it would help a lot if I could isolate the various components from each other, and especially from the metal body of the fridge. I first tried using some rubber sheeting I had (actually old MTB tubes), but that didn’t work at all (not thick enough). Then I hit the local hardware store to get some rubber washers and grommets. I installed the washers to both sides of the clips that hold the coil assembly to the mounting bracket. (An extra tip is to make sure the coil mounting screws aren’t too tight, to further reduce the transmission of vibration.) I got thicker rubber grommets to use between the mounting bracket at the refrigerator body itself. Basically trying to isolate any metal to metal contact. Finally, I zip-tied the whole assembly together to reduce vibration even more. End result was a huge improvement in noise for what was a pretty easy mod.

I do still get some vibration transmitted through the refrigerator cabinet itself, which I plan to address in the spring by adding some sort of foam padding to isolate the fridge as a whole from the wood. I’m pretty confident that should do the trick to get it really quiet.

[bigriver]

Super useful info that a whole lot of folks will appreciate. Thanks for the contribution Brian!

[boywonder]

McMaster sells vibration isolating mounts in many styles; they isolate the threaded mounts on either end, and as you found out that makes a big difference.

One issue with these is that with horizontal mounting they can sag, especially when designing for max isolation. You can go with beefier units to minimize sag at the expense of less isolation, it's all a trade-off.

McMaster has many other styles than what I cut and pasted below, but these give you the idea.

..in both inch and metric threads.....

[boywonder]

Originally Posted by BrianW

The noise begins when the compressor kicks on, creating a sort of harmonic vibration that creates rattles and transfers to the van through the refrigerator cabinet wood.

End result was a huge improvement in noise for what was a pretty easy mod.

I do still get some vibration transmitted through the refrigerator cabinet itself, which I plan to address in the spring by adding some sort of foam padding to isolate the fridge as a whole from the wood. I’m pretty confident that should do the trick to get it really quiet.

Applying some damping sheet (the peel and stick stuff) to the sheetmetal will make a difference as well if you are hearing metal surface resonances. For cheap you can use peel and stick window flashing, or the fancy stuff sold for sound damping.

If you use foam try to find peel and stick damping sheet with foam attached. Foam doesn't attenuate the sheet metal resonances; it's mostly used to attenuate high frequency sound in enclosures. The gooey glue layer between the damping sheet and the sheet metal kills the enclosure resonances better. When the panel vibrates, it moves the glue layer back and forth in shear, heating up the glue layer. That's how you remove the vibration energy.

[BrianW]

That a good idea to use the dampening sheets. I have some left over from installing new speakers in the front door. I was mainly planning to install it on the shelf where the frig sits, but adding it to the fridge’s metal itself isn’t a bad idea. Although there really isn’t room on the sides because it’s a tight fit when it slides in.

[boywonder]

It appears that you could install some damping sheet right on the sheet metal where the compressor is mounted. It still is quite effective if cut into strips, shapes etc. so maybe no need to unbolt the compressor, just peel and stick around it. Cover as much of the panel as you can.

If you were doing it scientifically you could superglue a small USB accelerometer to various places on the panel to find the max amplitude areas (the panel has a least one resonance mode with areas of large panel deflections and some areas with no movement...nulls...just like a guitar string or piano string) and stick the sheet there. This work is sometimes done in development to save $$ on damping sheet when you are building large quantities.

But screw that, just cover as much as you can with damping sheet......it should help.