AC Beat Frequency

[Cate&Rob]

Jlawles2 Joseph,

Great input! I never thought to cross check the beat frequency with the line voltage. Which is easy for me to do with the meters that you suggested! I think I can access frequency on my EMS.
Thanks!

Rob

[Jlawles2]

Rob, Don't confuse voltage and frequency. Remember both hot legs are generated at the same time so any frequency variance will be present in both legs. I don't know where you are in FL, but there are 3 large power plants that I know of and all will experience the same period of frequency. It's actually very predictable and the plants have software that help manage it.

Note the three plants are outside Tampa, South of Jacksonville, and South of Miami. There may be others, but those are the ones I know of. The closer you are to one, I would imagine the more prevalent the period in frequency.

[Jkwilson]

Just one AC . . . so, nothing to compare to.

Rob

I'm wondering about duct work. We had an issue with vibration from a coolant pump feeding an improper flex line. As flow rose, the line expanded, but when the line stopped expanding the pump eased up due to the increase in pressure causing the line to contract a little. It set up a little pressure loop that caused the cabinet to vibrate.

[TedS]

Rob, Don't confuse voltage and frequency. Remember both hot legs are generated at the same time so any frequency variance will be present in both legs. I don't know where you are in FL, but there are 3 large power plants that I know of and all will experience the same period of frequency. It's actually very predictable and the plants have software that help manage it.

Note the three plants are outside Tampa, South of Jacksonville, and South of Miami. There may be others, but those are the ones I know of. The closer you are to one, I would imagine the more prevalent the period in frequency.

Right. There will be no frequency difference between legs. The feed is split phase from one side of the transformer.

[Canyonlight]

Rob - as John shared we have not experienced this type of sound either. And yes, while you have a 100,000K miles on your rear AC lol, we are barely broken in especially since we added the front AC in 2018.

Will be curious to see what you determine just in case we do, to see what we may need to consider. I am guessing that Cate has not noticed nor have Angel and Molly reacted in any way.

Dan

[Scott'n'Wendy]

Rp The frequency of the power grid is cyclic, it has a period to it where it fluctuates between about 58 Hz and 62 Hz.

It is not cyclic if you mean it varies up and down from 58 to 62 hz regularly. It is a very steady 60hz cycle though... lol
An Unexpected VERY high load can cause a frequency issue.

[TedS]

Rather than a beat frequency, there may be an unstable motor speed due to an unstable load varying at the 1 cps rate. Motor hunting. That could sound like a beat frequency.

[Scott'n'Wendy]

A bearing or other friction issue could would cause additional motor slip, which would change the motor rotation speed, but I have a hard time logically connecting that to the described problem.
Amperage would increase. Do you have a clip on ammeter Rob? Take a reading after running a minute then another when the issue shows up? If it's a couple amps higher..2 or 3.... could be a clue.

[Cate&Rob]

Rather than a beat frequency, there may be an unstable motor speed due to an unstable load varying at the 1 cps rate. Motor hunting. That could sound like a beat frequency.

Hi Ted,

"Motor hunting" is the best description of this noise. It seems to have something to do with extended compressor run time. We are currently heading north, temperatures have cooled and the AC compressor cycles to maintain set temp. The noise is gone .

Rob

[AlexPeterson]

Cate&Rob It might possibly be helpful to install an app like "Spectroid" on your phone. This will allow you to see the various frequencies of sound. Here is an example of a screen shot of it on my phone. The vertical purple lines are running traces of the various peaks of frequencies recorded. This trace is from a very quiet room. Your A/C should jump out, as well as the beat freq you are hearing. If not helpful in solving the problem, it will be fun!