Tracking down a vibration

[desA]

I've got a small unit - approximately 700x700x750mm, with a single scroll compressor (rubber mounted on factory-supplied mounts), fan mounted onto the casing (box front) - no rubber mounts.

I'm getting a small niggling vibration that seems to work its way towards the rear of the unit. It seems to rise up in level, then drop off. I've listened to the compressor - nothing out of the ordinary. Touching the piping seems to show the vibration coming off (or onto) the discharge line, & tracking down two long, thin service ports.

I've a keen ear & hate a vibration, no matter how small - it's not a lot - just irritating to my ear.

What I had thought about was fan-to-compressor interaction eg. beats, where the frequencies are coupling at times to track through a vibration. The other alternative is a check valve in the discharge line - mounted in a vertical upleg - 180 degree loops bottom & top - some 300mm away from check valve.

Another thought was to add mass in the right places. I've seen rubber mass dampers installed on the suction line of rotary compressors, for instance.

I'd appreciate advice on how to track down the real origin of the vibration & simple ways on how to solve it.

[tony--1]

have you tryed running fan and comp separately to see where it is coming from ? . not for to long just to test

[ice_cold]

Instead of tracking down the source of vibration, you may try adding some mass to the suspicious parts one by one, and see if it cuts off the irritating noise.
In my opinion it may be quicker and more practical rather than tracking down.
Please inform us about the result.

[desA]

have you tryed running fan and comp separately to see where it is coming from ? . not for to long just to test

That's a very valid idea. It makes good sense - then it can be established if either one is creating the problem, or their combination.

I'll do that & report back. Thanks very much.

I also plan to install rubber washers either side of the fan bolts, & a fan speed modulator, to adjust fan speed (beats de-coupling).

I've done all the obvious stuff like check that the compressor, piping is not touching the case - no issues here.

The noise seems to eventually amplify through the evaporator, near the return end - after having traveled through the discharge pipework, but it's difficult to pin down - comes & goes.

[desA]

Instead of tracking down the source of vibration, you may try adding some mass to the suspicious parts one by one, and see if it cuts off the irritating noise.
In my opinion it may be quicker and more practical rather than tracking down.
Please inform us about the result.

I've started adding on certain pipes, but so far, this has not helped. The trick will always be to find the right spot...

I see that some rotary compressor manufacturers (eg. LG) advise use of a heavy rubber mass damper on the suction line.

[chemi-cool]

Vibration is a pain and usually ends in a cracked tube.

Fan and compressor are working together so its important to find the vibration when they are both running.

Copper tubing has a different design for a recip, scroll or rotary.
Changing direction of rotation can help at times but you are having a scroll so it doesn't work.

How about tightening the compressor to the base using hard rubber blocks?
Changing the tubes layout?