harmonic distortion

[hvac01453]

I have been servicing an old Lennox heaper 80's vintage... and have a harmonic distortion that hums in the space. It only happens when the refrigeration circuit is operating. I even disconnected the condenser fan motor in the event vibration was comming from there. I installed a muffler in the event it was pulsations, to no avail. The only other thing I was thinking it cold be, is the metering device...I doubt the dryer would do that...Oh...the unit was low on charge and when up to full charge, the hum was even louder...I checked the rubber mounts on the compressor and they seem fine. I don't feel any vibration in the tubing with my hands either... any ideas? mad:

[herefishy]

By harmonic distortion, I guess your saying that it's noisy.

If it is a hermetic compressor, a spring of the motor-compressor suspension may be broken. Use a long screwdriver to place against your ear and the compressor shell and you may "hear" that the noise is emitting from the internal works of the compressor (or I guess you could get one of those automotive stethoscopes - the screwdriver does me fine).

[Argus]

If it's any guidance, I encountered a similar problem from your description many, many years ago on a beer cellar in the UK that was cooled with an old York hermetic. In my experience it is comparatively rare in refrigeration systems.

The problem was intermittent, it came and went and sure enough, it never occurred when the engineer was present.

In this instance it was LOUD- about the same intensity as a car horn. I had packed up and left the job thinking another abortive visit and I could hear it in the street. When I finally tracked it down, it was the TX valve. I concluded that the seat and needle arrangement was worn sufficiently for it to vibrate and cause a constantly pitched whine, like a single note on a church organ, though it seemed to favour a particular range of pressures in the liquid line and evaporator, because it came and went and seemed to be dependent on the valve position.

You get the same effect more frequently with water valves that tend to ‘hoot’ when the valve stem is loose against the seat.

In short if it is anywhere near the evaporator, check the TXV, though the noise can tend to travel around the system.

Good luck

[hvac01453]

A single note like an organ is a good discription, a whine or horn like sound is also just what it sounds like. I had this same problem on a Liebert split years ago, and the muffler did the trick although it was a refrigerant pipe that was making the sound going through a space...The TXV is the only thing I think left capable to make the pitched tone! Thanks for the replys!

[Argus]

No problem. Please let me know if it is successful.

Modern valves tend to be better machined than the older varieties, so it's rare problem these days. but a small valve can make a considerable racket........

To pinpoint the trouble, pumping the unit down while it is sounding off should make it go away because if it is a worn stem or seat, the harmonic noise is a vibration hammer and is pressure dependent. It should then return when the valve assumes the previous stem positions.

[hvac01453]

the customer won't spend anymore on the unit till something more serious happens to it....I'll change it out the next time I open the system, or do serious work to it. They're cheap and dont want to buy a new one....You know how that goes...

[adacus1]

the same can occur with high pressure regulators in compressor discharge lines those that ensure a minimum discharge pressure. On very low flow rates they can make anything from a low pitch hum to a 'screech' as they open and close rapidly