Condensing unit noise

[kwired]

Maybe I should clarify something. What is slugging? An industry term for liquid making it back on the suction of compressor. When liquid gets in a scroll, it is way more dense than a gas, causing an imbalance, thus noise. Then stupid techs say the noise is normal. TF it is! It is true there is a slight buzz to a scroll. Normal. Noises that come and go, not normal usually.

It would also have to pass through the compressor without changing loading of the compressor or input current should change. Liquid going through a compressor is like having a positive displacement pump. But here there is likely still enough gas in the mix to keep it from becoming too extreme compression wise.

 

[fastline]

The sound must entirely be coming from the refrigeration circuit then. Any change in sound from the motor likely is because of change of load on it, or a change of input voltage which should ultimately change the load as well.

Have no idea why the voltage would be a consideration. Again, chasing this on the electrical side is ridiculous. Install the proper sensors and check the refrigeration cycle.

 

[Eddie702]

I don't know what the OP is hearing it could be a buzzing contactor. They get dirt in them and a little rust and they can buzz. But that noise is usually steady but the OP mentioned tapping the contactor so that is a possible problem.

As far as what @fastline mentioned he is correct that most techs "gas & go" and as a result the unit may not have the correct charge. They don't spend time looking for leaks which they should do.

A unit with correct charge and clean coils and filters and the correct airflow (no undersized ducts) can last 30 or 40 years with some regular maintenance.

And as @fastline mentioned compressor amps is only one piece of the puzzle. The tech has to look at superheat, subcooling and operating temp and pressures.

The compressor motor is cooled by the suction gas so if things are not right the compressor will suffer.. Scroll compressors are rotation sensitive, not an issue with single phase.

We had a new job where the GC wanted cooling and fired up 15 3 phase scroll compressors without having HVAC check them an expensive mistake. he was about 1/2 right and 1/2 wrong.

If the rotation is wrong the compressor will draw low amps and will not pump and will fail after a few min of run time.

 

[kwired]

Have no idea why the voltage would be a consideration. Again, chasing this on the electrical side is ridiculous. Install the proper sensors and check the refrigeration cycle.

It would change how much current the motor draws. I'll admit I probably don't know enough about this "slugging" and how it may effect loading of the compressor, but I do understand motors and an induction motor motor will change current draw if either the volts, frequency, or driven load changes. this slugging sure sounds like it should change the driven load, even if only slightly for a short time but maybe it is minor enough that it is not easy to measure without more sensitive equipment? Liquids don't compress, but if there is still gas surrounding it then it would just compress that gas to more extent than if there were no liquid within it. I could see this being a lesser issue with a scroll compressor than a piston compressor but it still is likely to increase input power needed to some extent during the time it occurs.