Resonant frequency = eureka insight?

[john-hvac-new]

I think that resonance has something, maybe a lot, to do with the strong vibration, in heat mode, of my new, all aluminum indoor coil (plus the original line set).

The old coil was copper tube with aluminum fins. The new coil is all aluminum. That changes not only the weight but also the mechanical characteristics of the coil.

It's reasonable to assume that with this change, the resonant frequency of the system has dropped (or risen) - possibly so that it now matches the pulse rate of the compressor.

High side pressure is also a factor since the vibration is worse in heat mode, and worst of all with high outdoor and indoor temperatures.

Here is a link to an article titled "Installation and Maintenance Instructions for Air-Cooled, Remote and Water-Cooled Condensing Units":

http://www.trentonrefrigeration.com/products/Cond_Units/tcu_im.pdf

Although the article is about condensing units, it has a paragraph on the use of a discharge muffler to minimize the effects of resonance and pressure.

"A DISCHARGE MUFFLER may be used to help minimize the noise created in the discharge line of the
compressor. This noise my be the result of variations in piping configuration, the pattern of the gas flow, line sizes, operating pressures or compressor and unit mounting. A particular combination of gas flow and piping will result in a resonant frequency, which may amplify the sound and vibration to an undesirable level. Gas pulsations from the compressor discharge may also be amplified in a similar manner."

[the dangling wrangler]

New contractor can't figure it out,can he?

[john-hvac-new]

New contractor can't figure it out,can he?

That's pretty accurate - for the original contractor.

The new contractor's service manager is waiting on the Goodman rep before coming out to look at the system.

However, he did mention a device that they have which can be inserted in the line set, at the condenser, to reduce the vibration - so - I think he is already 'there' as far as what might be wrong and how to fix it.

I can see how this might be a fairly rare result - that changing from one coil type to another would change the system resonance of a system just enough to cause problems.

But still, I am disappointed that my original contractor, who is a pretty smart guy, didn't think of it - and basically gave up.

[the dangling wrangler]

Sounds like either a muffler, or vibration isolator.