Condensing unit noise

fastline said:
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.
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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.
 
kwired said:
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.
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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.
 
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.
 
fastline said:
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.
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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.
 
Slugging is when liquid gets back to the compressor. This can be cause by dirty air filter, dirty evaporator, overcharge, defective metering devise passing too much liquid etc. Compressors are only made to pump gas. Any liquid will have the potential to crash the compressor....trying to compress an incompressible liquid.

The noise is unmistakable and is the kind of noise that would tell even a no HVAC person to "shut it off"
 
kwired said:
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.
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You seem very hung up on your theories. I suggest you go try that out and report back. Tell any HVAC guy that you "confirmed slugging by seeing higher amps on the compressor". They will all get a good laugh. You can't!
 
Eddie702 said:
Slugging is when liquid gets back to the compressor. This can be cause by dirty air filter, dirty evaporator, overcharge, defective metering devise passing too much liquid etc. Compressors are only made to pump gas. Any liquid will have the potential to crash the compressor....trying to compress an incompressible liquid.

The noise is unmistakable and is the kind of noise that would tell even a no HVAC person to "shut it off"
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As you are probably aware, there are different levels of slugging. Very minor to very major. Sometimes superheat will indicate major concerns, yet there are no noises. Some noises are indeed confirmed from a bad compressor, bad isolators, etc.
 
Thank you guys for all the help!

I'm still on vacation, but I'll contact another tech I am friends with and run some of this hvac jargon past him and see if he can help me out.

Fastline, you mentioned that I may have a plugged coil. How does one remedy such an issue? It just so happens that the tech added leak stop to the system after charging it. Maybe this solution caused this issue??
 
mark32 said:
Thank you guys for all the help!

I'm still on vacation, but I'll contact another tech I am friends with and run some of this hvac jargon past him and see if he can help me out.

Fastline, you mentioned that I may have a plugged coil. How does one remedy such an issue? It just so happens that the tech added leak stop to the system after charging it. Maybe this solution caused this issue??
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I think he was talking about the air side of the coil
 
Thank you Eddie!

Okay, I see what you mean. I thought the coils were pretty clean, as I hose it down once I see those fins getting clogged. But, he did use a coil cleaner regardless, as that's something he always does when servicing a unit.
 
mark32 said:
Thank you Eddie!

Okay, I see what you mean. I thought the coils were pretty clean, as I hose it down once I see those fins getting clogged. But, he did use a coil cleaner regardless, as that's something he always does when servicing a unit.
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No, what you missed in my posts is the word "EVAP", as in evaporator coil. As in the one indoors that you totally ignore, and all techs do too. It is pointless to even attempt to look at it unless it is easy and you know what to look for. Otherwise pressures and temps in the system will tell the story.

As for the stop leak, blah! That ain't even cool! That right there can clog a TXV, and certainly cause slugging. That should always be a last resort in a system because it usually destroys them rather than fixes them. Consider it like the "experimental injection" for an illness that is terminal.
 
fastline said:
You seem very hung up on your theories. I suggest you go try that out and report back. Tell any HVAC guy that you "confirmed slugging by seeing higher amps on the compressor". They will all get a good laugh. You can't!
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I don't think I ever said anything about confirming slugging by seeing higher amps. I certainly did not intend that if I did or was misunderstood. My thoughts on this were that slugging likely should put more load on the compressor and if so should increase amp draw. That is how induction motors work the more torque is being demanded the more input current they draw.

This slugging apparently doesn't load the motor like I think it would and the sound that was mentioned way back early in the thread probably is sound in the refrigerant circuit more so than sound being made by the motor itself if it this is what is happening. That said I find it hard to believe it doesn't change the load on the motor at all just might not be all that significant of a change, liquids will not compress and that should have some effect in how the compressor is loaded. Small amounts of liquid within a considerable volume of gas may not be to big of a factor. Even an air compressor has to deal with this as moisture in the air will condense as the air is compressed.
 
kwired said:
I don't think I ever said anything about confirming slugging by seeing higher amps. I certainly did not intend that if I did or was misunderstood. My thoughts on this were that slugging likely should put more load on the compressor and if so should increase amp draw. That is how induction motors work the more torque is being demanded the more input current they draw.

This slugging apparently doesn't load the motor like I think it would and the sound that was mentioned way back early in the thread probably is sound in the refrigerant circuit more so than sound being made by the motor itself if it this is what is happening. That said I find it hard to believe it doesn't change the load on the motor at all just might not be all that significant of a change, liquids will not compress and that should have some effect in how the compressor is loaded. Small amounts of liquid within a considerable volume of gas may not be to big of a factor. Even an air compressor has to deal with this as moisture in the air will condense as the air is compressed.
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I brought up slugging as only a 'potential' source of noise. However, all I am trying to tell you as someone with countless belt notches in the field, the current of a compressor is DYNAMIC. As in, it's all over the place depending on load conditions, and you cannot begin to 'predict' any level of current as being an indicator of flood back. This is why we use pressure/temp sensors, not an amp meter, to detect the concern.
 
fastline said:
I brought up slugging as only a 'potential' source of noise. However, all I am trying to tell you as someone with countless belt notches in the field, the current of a compressor is DYNAMIC. As in, it's all over the place depending on load conditions, and you cannot begin to 'predict' any level of current as being an indicator of flood back. This is why we use pressure/temp sensors, not an amp meter, to detect the concern.
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I spoke with yet another hvac guy in my contacts list, and while he also couldn't confirm if the noise is due to slugging (I was able to send him a video showcasing the noise) he echoed your advice in stating the system needs to be pressurized to determine where the leak is, then fix the leak, then recharge the system. (I'm guessing the stop leak would be expelled during pressurization? He also didn't like the fact the guy used it) However, this guy is now retired and no longer has the equipment to make this happen. So, I'll ask around my circles and see if one can help me out here.
 
mark32 said:
I spoke with yet another hvac guy in my contacts list, and while he also couldn't confirm if the noise is due to slugging (I was able to send him a video showcasing the noise) he echoed your advice in stating the system needs to be pressurized to determine where the leak is, then fix the leak, then recharge the system. (I'm guessing the stop leak would be expelled during pressurization? He also didn't like the fact the guy used it) However, this guy is now retired and no longer has the equipment to make this happen. So, I'll ask around my circles and see if one can help me out here.
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Some of the stop leak will come out with the charge, but some will be stuck in system. You would not evac the system to chase the leak, you just get your sniffer and other tools going and see if you can spot the leak just as it runs. If/when that is detected, then you make a plan. Sometimes that plan is replacement. Lots of factors. What is common is leaks in the evap or the service valves/ports. I typically will look for leaks around valves before EVER installing gauges. Just watch online vids to realize just how rare that is!

In many service calls, the system has lost some charge, and those schrader valves are well known to leak.

It would be real important to know if system has needed charge before, and how much was put in system recently to get it back to design charge. Trying to assess the magnitude of the leak.

Once your new guy hooks on to system, get him to snapshot the parameters such as what I attached from one of mine. Would also need to know the load conditions such as ambient dry bulb and indoor wet/dry bulb. Basically as much data as possible. But if you have a good tech, they will prob be on the hunt for any culprits, and be all over a repair BUT, I like to save this data so there is no BS about what the issue "was", and how it got fixed.

I've seen countless idiots overcharge equipment because they could not tell on their gauges, the difference between low charge and a bad TXV. Having good service records is important.
 

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herding_cats said:
replace the contactor with a type the has a noise filter for the coil. ABB makes the best one for that.
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Good advise, I have replaced old contactors only to find the new ones also buzz. Not just on HVAC either.
One thing you could do to isolate the source of the buzzing is temp some wire leads on to move the contactor out of the unit.
 
Thanks once more for the help fastline!

This would be the third charge for this 13 year old system. The first charge was six years ago, and the second was three years ago. So, it appears I get three years out of a charge. My concern at this point, however, is no longer the leak, but trying to save the compressor (In turn, saving me money). We have a service contract with the company that installed the unit (Which happens to be a segment of the local power company) but of course, they wanted to change the whole unit when they came out to look, and of course, none of the work would be covered, not even the labor if they were to just give us a charge. This kind of left a bad taste in my mouth, so I figured I'd give the work to one of my co-workers. Who thought it would lead to possible issues, although, it could be just a coincidence that the compressor acted up on it's own.
 
I've never seen those service agreement situations ever really work out for the owner. Seems to always be language that would deny any real repairs. You have a leak. That is likely documented. These systems should not leak. It should have been addressed 6y ago, somehow. IDK how many lbs they are adding, but you're probably like others where you don't call until it finally won't do much, so that would lead me to think several lbs of gas.

What I might recommend is uploading a private vid on youtube and dropping a link here so I can hear it. Other is that you really need someone with competence, not a scam tech, to eval the system. You might get lucky and the stop leak works, but all other parameters of the system should be checked. For all you know, the evap just needs a good cleaning. They really suck to clean on some, but so very worth it!

Something you can do by yourself is get some Big Blue or comparable bubble solution and see if you can get lucky. First place I would go is those service valves. Here is another trick I have used. I put a balloon around each service port and see if they try to inflate after days. With a small leak, you likely would not see a leak in an instant, it takes time. Another leak area is the TXV valve near the evap coil. It would be under the sheet metal. I've got lucky on a couple where a flare nut was leaking and a little tightening fixed it. But you have to be careful there. Tighten nothing unless you can confirm a leak though.

But really, the smartest thing you could do is ignore the "favor friend" resources, and ignore the service contract idiots they want to send, and find a well vetted, 40-50yo independent tech, and be onsite with him to go over it. Unlike bigger companies that suck people into their web of BS with "free tune ups", independents rely on word of mouth and skill to get business. The rookies work in the big companies. The good ones venture out on their own. They could not survive with no ability. The even smarter ones get out of residential work all together! lol
 
Techs used to carry a bottle of Nitrogen and I think test the system with that overnight or something. I agree with pumping down the system and weighing whats in there.
 
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