Condensing unit noise

[mark32]

Hello all,

I recently noticed that the a/c condensing unit at my townhouse makes a noise, intermittently, as it's running. The noise itself is hard to describe, but I'd say it's similar to the hum of a transformer, but a bit more pronounced, if that makes sense. Anyway, the noise will show itself, last about 5 - 10 seconds and fade away, only to reappear within seconds to a minute or so again later. This happens throughout the cooling cycle. I put my meter on it, and it steadily draws 6.5 amps, whether it's making this noise or running quietly. This unit is 13 years old and appears to be functioning properly otherwise. The specs on the compressor are 14.1 RLA and is rated for 208 - 230v. However, at the time of testing, the supplied voltage was 245v. I'm not sure if this is a dire situation or I can let it be. I just want to address this in an effort to both quiet it down and increase it's life expectancy. I did change the cap, but it didn't do the trick. Thanks!

 

[hbiss]

I wouldn't worry about the 245. 13 years ago 230 was the standard. Now it's 250. I think the noise is probably just sheet metal vibrating or the fan. Have you had a HVAC guy come and put gauges on it just for a checkup?

-Hal

 

[Ken_S]

Check the contactor, if it's not seating properly it will produce the 60 cycle humming noise you're talking about.

 

[mark32]

Thanks guys! As a matter of fact Hal....I did have an a/c tech acquaintance charge it up like two weeks before I became aware of this noise (Seems like we need a charge every three years). As a side note, the fan itself is smooth as can be. Ken, that's a good idea, I will open it up and see if I can tell if the noise originates from the contactor or not. Not sure if this helps, but what initially alerted me to this condition is, I heard this noise/vibration on the line set that runs into a closet in my room. (The line set, in total, is less than 20' in length)

 

[Little Bill]

Thanks guys! As a matter of fact Hal....I did have an a/c tech acquaintance charge it up like two weeks before I became aware of this noise (Seems like we need a charge every three years). As a side note, the fan itself is smooth as can be. Ken, that's a good idea, I will open it up and see if I can tell if the noise originates from the contactor or not. Not sure if this helps, but what initially alerted me to this condition is, I heard this noise/vibration on the line set that runs into a closet in my room. (The line set, in total, is less than 20' in length)

Check the line set from the unit to inside. Some of the insulation could be worn off and the noise you hear could just be vibration from the metal of the line set contacting something.

 

[herding_cats]

replace the contactor with a type the has a noise filter for the coil. ABB makes the best one for that.

 

[Eddie702]

Have them recheck the charge he may have overcharged it. You shouldn't get any vibration in the line set. If you do you could be looking for more leaks shortly.

I am assuming this is a straight AC unit. Ask the tech if it has an expansion valve or a piston at the indoor coil. The charging procedures for each one is different. TXVs get charged to subcooling and a piston gets charged to superheat.

His answers to you may point to weather he knows what he is doing ............or not. If he just put gauges on and jambed some gas in it without any other measurements it could be a problem

 

[mark32]

Thanks again for the replies! I just took the cover off the unit, and the noise is indeed coming from the compressor.

Little Bill, I'm guessing I sense this condition in the line set as it's such a short run, it appears to be well insulated.

Eddie, yes, this unit is just a/c. The guy did hook up his gauges and watched them as he charged the system. He didn't take the cover off to look for additional components as you pointed out though. He comes from a commercial background, not sure if that matters or not. I'm sure he'd stop by to recheck if I ask him too, but it would sound as if I'm questioning his work. The info you speak of is not listed on the nameplate? I'll take a pic of the internals and post it. Thanks again~

 

[mark32]

Here you go. I tried uploading a 1 second video, but the site says it' too large

 

[retirede]

Thanks again for the replies! I just took the cover off the unit, and the noise is indeed coming from the compressor.

Little Bill, I'm guessing I sense this condition in the line set as it's such a short run, it appears to be well insulated.

Eddie, yes, this unit is just a/c. The guy did hook up his gauges and watched them as he charged the system. He didn't take the cover off to look for additional components as you pointed out though. He comes from a commercial background, not sure if that matters or not. I'm sure he'd stop by to recheck if I ask him too, but it would sound as if I'm questioning his work. The info you speak of is not listed on the nameplate? I'll take a pic of the internals and post it. Thanks again~

If he didn’t remove all of the refrigerant and put the correct amount (by weight) back in, it’s not right. You can’t just go by pressures like you used to be able to with R12.

 

[mark32]

Thank you retirede! I'm not sure if he initially reclaimed the refrigerant or not, but I do know he didn't have a scale with him. Hmm, I just remembered a former neighbor of mine is an a/c tech. I'm going to send him the video and see what he says.

 

[Eddie702]

Compressor could be on its way out or he may have over charged it. Knowing it has a leak and is recharged occasionally some think "a little more" is better" but it isn't. The lineset vibrating is not normal.

Usually inside the panel cover there are instructions for charging. There are different methods depending on what components you have,. If not on the panel cover it is in the manual.

Weighing in the charge for a split system is not that accurate. You have to estimate the line length etc. Weighing the charge is more for package units, Split systems, weighing the initial charge in is ok the superheat or subcooling measurements are taken to get the right charge. I was an HVAC tech 46 years.

 

[mark32]

Just an update. So, I spoke with a few more hvac techs, and one suggested changing the contactor as the noise seemed to abruptly stop if I tap on the contactor itself once the noise in question started up. (This was a troubleshooting suggestion on his part). However, the noise continued with the new contactor. Another tech said "Scroll" compressors are known to be noisy. All in all, non of the techs I questioned seemed alarmed or overly concerned, and some mentioned that with it's age (13 years old) it's not out of the question for it to be a bit noisy. So, I guess I just let it ride and see what takes place down the road. I'm currently away on vacation, so I'll see if anything has changed once I return home next week.

Ps, I intended on posting this back when this thread was current, but it seemed like the site was down for a few days.

 

[fastline]

I'm licensed in HVAC. Likely you are slugging the compressor because someone did the 'gas n go'. It's not an electrical problem, it's a refrigeration problem. Called a plugged coil. But that takes more than 5min to fix.

No I would not "let it ride".

 

[kwired]

I'm licensed in HVAC. Likely you are slugging the compressor because someone did the 'gas n go'. It's not an electrical problem, it's a refrigeration problem. Called a plugged coil. But that takes more than 5min to fix.

No I would not "let it ride".

But shouldn't any sort of issue that changes loading of the compressor (even if for short time period) cause a change in running current during that time? Could be increase or a decrease in current, just depends on what the issue is and how it affects loading of the compressor. In OP he indicated current remained steady when the sound in question was occurring.

 

[fastline]

But shouldn't any sort of issue that changes loading of the compressor (even if for short time period) cause a change in running current during that time? Could be increase or a decrease in current, just depends on what the issue is and how it affects loading of the compressor. In OP he indicated current remained steady when the sound in question was occurring.

It's not something you will see on a meter. As compression ratio changes, indeed, current will change, but you will not capture a slugging event with a meter.

I hear crap all the time from techs "it's old, its a scroll, etc". Without a competent inspection, that is guesswork. Slugging can, does, and will kill a compressor. Then people say "it just died one day". Not, it was murdered in a slow and preventable death.

Hack techs add gas and run. Good techs find out why you need gas in the first place, if you really even do, and clean the coils, in which the evap is the one that is a real PITA.

 

[kwired]

It's not something you will see on a meter. As compression ratio changes, indeed, current will change, but you will not capture a slugging event with a meter.

I hear crap all the time from techs "it's old, its a scroll, etc". Without a competent inspection, that is guesswork. Slugging can, does, and will kill a compressor. Then people say "it just died one day". Not, it was murdered in a slow and preventable death.

Hack techs add gas and run. Good techs find out why you need gas in the first place, if you really even do, and clean the coils, in which the evap is the one that is a real PITA.

If is a significant enough thing to change the sound of the unit seems it would have a good chance of changing input current. Especially if it lasts several seconds or longer. Brief change- probably not going to catch without more precise metering equipment.

 

[fastline]

If is a significant enough thing to change the sound of the unit seems it would have a good chance of changing input current. Especially if it lasts several seconds or longer. Brief change- probably not going to catch without more precise metering equipment.

Nope, you are in dream land. Sure, it 'might' tickle a meter, but what number are you looking for? What is it telling you? This is no different than chasing a low voltage issue with an amp meter!

No, you put gauges on and check superheat and subcool, and all the other pressures/temps that can truly indicate system health. Checking current on a compressor is only one metric, and only loosely associated with health.

 

[fastline]

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.

 

[kwired]

Nope, you are in dream land. Sure, it 'might' tickle a meter, but what number are you looking for? What is it telling you? This is no different than chasing a low voltage issue with an amp meter!

No, you put gauges on and check superheat and subcool, and all the other pressures/temps that can truly indicate system health. Checking current on a compressor is only one metric, and only loosely associated with health.

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.