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Diagnose these noises: hiss, howl, huff, hum sounds at air conditioners or heat pumps or at heating systems & in HVAC duct systems or air handlers.
Air conditioner or heat pump noise diagnosis & cure: this air conditioning repair article discusses the diagnosis and repair of air conditioning compressor noises which range in importance from normal (if annoying squeaks and squeals, to rattling loose bolts and hardware, to costly compressor damage indicating air conditioning compressor or A/C compressors at or near end of their life.
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The following HVAC noise descriptions are a continuation from the article beginning at NOISES, HVAC SOUND DESCRIPTIONS
Hissing sound and humming from my AC - It was the capacitor! Thanks! - Bingo
Question: Hissing Compressor noises, ice on the suction line, hissing ssssss sounds from air conditioner
sir i check my out door unit i see the compressor is getting cold and after few minutes the amperes will going up start in 17 up to 20amp.,and it comes sound like noise, yes that was my compressor also, din after few minutes suck line becomes ice and noise coming like ssssssssssssssssssssssssssssssssssssssssss..... - Danny Carumba
Watch out: Danny: Because SOME A/C compressor hissing noises can be due to dangerous internal over-pressure conditions, I'd ask a service technician to check the air conditioner promptly. Please see our catalog of sources of hissing sounds in air conditioners and heat pumps, described at SCREAMING A/C compressor/condenser unit sounds. Such equipment should be shut off immediately.
Question: Hissing in "surround sound" after installing a new high efficiency A/C and Heating System
I have a very high pitch hissing sound "surround sound" throughout the whole condo. We did install a new /better/efficient AC/heating system...some original duct and tubing is still in place. The problem is, we can't sleep with this noise! And cannot pinpoint where its's coming from: wall.
I need a professional with GOOD hearing to hear this. We will be putting some sound proofing on the garage back wall that abuts, unfortunately the condo (6 units attached) doghouse. We have had all items on the wall of the doghouse shut off and can STILL hear this high pitch hissing? Any suggestions to what we can do and WHO to contact?
Have had 2 electricians, and audiologist, etc. check this but their hearing is not like mine and I do not have tinnitis, because when out and about I hear fine and not the hissing. HELP please. I really don't want to move. - El
Reply: Track down sound source before installing soundproofing around an A/C or heat pump system
El, before installing soundproofing it makes sense to track down the source of the annoying noise - especially since the noise, if abnormal, could indicate failing or even unsafe equipment that needs repair.
We discussed hissing at the compressor condenser unit at SCREAMING A/C and warned about this problem in the article above. But not all hissing is due to extreme pressure. An A/C or heat pump compressor (of the reciprocating or piston and cylinder design) that continues to run with damaged internal refrigerant valves may make a hissing noise too. In this case the motor will continue to run, it may not even overheat, but it's wasting electricity and running more than it should.
An HVAC tech may diagnose bad A/C compressor valves by noticing that the high and low side pressures equalize very quickly when the motor stops.
Hi Dan ...thank you for responding to my question. I cannot track down the source - it's Surround sound - everywhere - not emanating from one spot unfortunately! I do live in a condo setting, had the Condo president shut off all electrical items in the doghouse: housing of the electrical, pumps, phone, etc. Shutdown could still hear the noise!
It seems no one can hear this ...except my family and none of us are in a business to locate the source.
We do have all underground lights, no poles. I have tried earplugs even, I don't have tinnitis, because when I am not inside the condo - no problem. Electricians and even PSNH don't seem to hear the very high pitch noise. If I could locate the source: one spot - I would gladly put a hole there.
I think until everyone else's' stuff starts breaking down so we can get a 5 for 1 deal this won't be fixed - and I know at this point the original builder is probably past the taking to court stage. Contractors who worked on these? To pass code IMO - barely. Any sources or websites you can suggest I'd appreciate. Thank you. EL
I would also like to mention that a Large PSNH box sits at the end of our driveway....they opened it up and changes a plug of sorts (???) not sure what, but also, a lot of underground cables under our particular front yard:PSNH, cable, etc. Itwould cost a lot know it would cost a lot , but don't feel we should have to pay since it (source)unknown still, is the cause. We also, have to contact Dig Safe prior to planting..
.I would think that the cable's, etc. would be way under , at least 4 or so feet...does anyone know building codes on cable depth necessary to pass codes in NH? If so please post here and info. as to contacts:web page , phone numbers, etc.
It seems to have increased as far as sound over the past 4-5yrs. We have also had a PSNH person come out to our condo to check our meter and it says with limits of Section PUC 304.02 by NHP Utilities (NHPUC), Chapter PUC 300, rules and reg's for electric utilities - really. I feel like I've exhausted my resources and I am not in this field...any thoughts to help? - El.
El, beginning at NOISE / SOUND DIAGNOSIS & CURE we organize some approaches to trying to track down odd sounds. To get anywhere with public officials or electricians they will of course need to either hear the sound themselves or confirm it with instruments.
Question: Hissing sound traced to a bad capacitor?
Hissing sound and humming from my AC - It was the capacitor! Thanks! - Bingo
Question: Hissing at compressor/condenser unit in hot weather, heavy load or after 5 minutes
I have a carrier 2000, don't know how many tons it is but here's the problem; I had a few hot days above 100 with abnormally high humidity. I turned on the AC in the early morning when it was relatively cool. It ran for 3 days straight with no issues. Then I noticed the air wasn't cool at all. Just warm and humid. I went outside to investigate.
The condenser was making an obnoxious humming and it sounded like the compressor had a blow of valve. It was hissing like it had a leak with a large amount of pressure behind it. I waited a couple days to turn it back on. It started fine the condenser sounded good and the fan started like it should and it was finally pumping out cold air. 5 minutes go by.
I hear the loud humming again and the hissing. So here is my question: Is my compressor shot or am I low on freon. Because it will over heat and shut down. Thanks for your help.
Reply: humming ususally means a motor is having trouble starting; hissing may be different.
Aaron: "The condenser was making an obnoxious humming and it sounded like the compressor had a blow of valve. It was hissing like it had a leak with a large amount of pressure behind it." suggests an overpressure at the compressor, perhaps a blocked condensing coil or dryer. Your system needs service, but the compressor is not necessarily shot - let us know what your tech says.
Dan: Thanks for the tip. By doing some research (and I am no HVAC guy by any means) I found that the compressor would indeed over heat because of too much pressure. I looked at the a coil in the furnace itself and it looked fine. I don't however understand " the dryer" factor. I did wash the outside of the unit before i started it and the air filter is spotless.
Reply: causes of hissing due to HVACR compressor over-pressure conditions
Aaron: if there is an overpressure at the compressor, a cause is usually a blockage somewhere. I don't know all possible causes, but some examples are
Other hissing sounds in HVAC systems may be traced to air duct leaks.
Reader Question: trouble tracking down a hissing noise at an Amana air handler w/ Goodman compressor/condenser - since original installation
3 months ago, I purchased an R-410A split system.
Since day 1 it has had a hissing problem. It is loud enough that people ask me what it is. The hissing comes from inside the air handler. The hiss starts as soon as you turn the unit on.
[The hissing sound] goes up in pitch for about 8 seconds, stays steady for 2 seconds, then goes down in pitch for about 8 seconds, and then there is no hiss for 2 seconds. Then it starts again and continues the cycle until the unit is turned off.
The fan running by itself doesn't make the hiss.
I have had 3 AC guys look at this and they can't figure it out. They only have guesses and want to do expensive things to try to figure it out. I can't afford that.
What gets me is they can't explain the 20 second cycle. It is like clockwork.
Any ideas? Thanks, Mark - 6/21/2014
Perhaps this is due to a sticking thermal expansion valve?
Reader follow-up: AC guy says "air in the system"
That is what I was thinking. Something wrong with the expansion valve.
The AC guys that have looked at it say it has air in the system because their gauges fluctuate from 279 and 304. But I would thing a bad TXV could cause that also???
I could understand air in the system making it act goofy, but to have something that is exactly 20 seconds every time sounds like a device of some sort messing up.
They want to vac the freon, put nitrogen in, then redo the freon for $966. Another AC guy said about $400. Either way, that is a lot of money for something that should be covered under warranty.
One of the sites I was on stated that you need to remove the TXV bulb before connecting the lines so you don't overheat it. They said if it is too hot to touch, you have already blown it. The AC guy didn't even use a quenching rag. But if it was blown, wouldn't it just stop working all together?
Your reasoning about the effects of air in the system is correct. Air is also a contaminant. It not only changes the operating property of the refrigerant gas, it also may add moisture.
Failure tomprotectmthe TEV from overheating during installation also violates the installation instructions and is likely to damage the valve.
Really? In all events, even the company's explanation, even if it were correct - which the logic of which is a bit foggy - would indicate improper original installation.
Refrigerant can leak out of a system for a variety of reasons that cause leaks in different locationsn some of which could be an installation error, but ambient pressure air does not leak *into* a pressurized refrigerant piping system. (Air can be introduced into a system by improper procedures in hooking up test equipment. )
If you realize that air in the system would, be mixed in with a gas and thus change its properties would be distributed throughout the system the pressure variation is not explained.
Conversely a sticking TEV, often caused by contaminants (such as debris from oxidized materials due to overheating) might cycle in its regulating performance, as the valve can frost up, then defrost, or can open not enough, or too much, causing changes in the high and low side pressures that in turn cause the valve to open or close again in response.
Electrical or control board component,failures might also cause cyclic behaviors ofmthe equipment, but in that cas we'd probably see corresponding changes in motor operation that would be easy to observe.
When the compressor runs continuously but,system pressure is varying its the refrigerant metering system (or a bad reversing valve) that come immediately to mind.
If you let them clean and recharge the system first without changing out the TEV there is a small chance that such a procedure would remove a contaminant fouling,the TEV (though I doubt it).
Since in all events we are talking about installation errors that one would think were under warranty (if they will agree) you could then let them go ahead.
Watch out about insisting on a particular repair. If you do that the company will decry any responsibility for, the success of the job (and may adopt a sloppy attitude that subverts the insisted on approach even if it should have worked).
While sometimes it is cheaper and faster to replace or change several things at once than to complete a detailed and precise problem problem diagnosis, in general what you want as the consumer is for the repair contractor to own responsibility for a correct and economical repair, without shotgunning the repair approach by doing unnecessary work at your expense.
Reader follow-up: making a recording of air conditioner hissing noise
Thanks for all the info. I will try a few more calls and see if I can find an AC guy that is a little more logical.
I have the system down right now to do plenum repairs, but when I get it back up I will try to make a recording and do a little more detailed diagnosis. I don't have the tools to do much, but I can see if it changes with the outdoor temp or indoor temp.
I will let you know how it goes.
I forgot to ask this. There is only a thin piece of insulation wrapped around the bulb/suction line and the insulation is open on both ends. I thought that was a little strange, but I found some pictures of other goodmans that were the same way. Would it hurt to put more insulation to see if it changes the hiss?
Also, If I take the TXV bulb loose from the suction line (to help narrow in on the problem) while it is running, will that damage anything?
I'd love to hear a recording and to add it to our diagnostic library. Moreso when we have a final diagnosis that makes sense of the sound.
This is a link to a youtube video of my AC problem. It is mostly just sound with little audio. I need to try a few variations to see what causes a change, but I thought this might trigger something in your mind from you past experience.
Are there any suggestions you have for making a better recording, like location of the mic, when it is cool outside or hot outside, cool inside or hot inside, windows open,.that sort of thing? Let me know if you can't access this video. I may need to make it public instead of private.
https://www.youtube.com/watch?v=i4iDxGiBfIM [this video is "private" and cannot be viewed at this link - Ed.]
I did notice that the compressor changes the sound that it makes just a little. Sounds like the load is changing. But it isn't as noticeable as the hiss inside. The recording makes the hiss sound worse than it is because I have the mic taped to the liquid line.
The liquid line is just a little warm and actually gets a little cool for a few seconds during the 23 second cycle.
Have you tried a mechanic's stethoscope?
Yes, but I don't have an electronic one. Had a hard time getting the mic to stay in position with the earpiece.
I just did the work about an hour ago, so it may be a fluke. Maybe the hiss will come back. I will let you know.
I thought it was strange that this even worked since the other pictures I have seen of goodman systems have the same small amount of insulation around the bulb.
Since the second AC guy said the system was overfilled and vented some freon, I would assume that it was correctly charged at some point, yet it has always made the hiss. With that said, what would be your hypothesis now that the extra insulation has made the system quiet but not fixed the split?
I'd figure the TEV is hissing, possibly not functioning perfectly. I'm not clear on why overcharging would cause that symptom. The TEV is metering liquid refrigerant on the high side of the system out into the cooling coil on the low side. It is designed to have liquid input and allow output of refrigerant that quickly changes to a gas - hence cooling the cooling coil.
I agree with you. But I am not sure how to get Goodman to fix it.
I think the second AC guy was ignoring the hissing and focusing on the low split. From what I have seen, most AC people (with the exclusion of you and a few others) don't appear to truly understand how the txv works (not that I do either). So, they try to ignore the txv and blame something they understand.
Just curious, do you have an engineering degree in something? You appear to be much more intelligent than most AC guys.
The split was 13-14 when he got here and 13-14 when he left. And I still had the hiss. So he didn't do me any good.
I would think that, since the temp of the air going over the coils doesn't change very fast, the txv should stay fairly steady, unless it has a problem.
Is this roughly 20 second cycle what they call txv hunting?
I have field exprience repairing HVACR systems, went to school on it, but am not an engineer and am not necessarily smarter than the other fellows you mention, but unlike some, I'm willing to read the instructions on the box rather than just use it to kneel upon. Also I've spent quite some time fielding and researching questions from InspectApedia readers.
The TEV is basically a thermostatically operated valve that opens to let refrigerant into the evaporator coil. Some of them are adjustable. Sometimes dirt or crud messes up the valve causing it to malfunction, ice up, or hiss.
We must keep in mind that guessing at a diagnostic when all I see is filtered through the pinhole of email means I'm just speculating.
PS: I wanted to add that your statement
"The liquid line is just a little warm and actually gets a little cool for a few seconds during the 23 second cycle."
may indicate a fluctuation in the TEV valve operation.
Howling Sounds from HVAC Systems: air conditioners, blower units, compressors, duct systems & heating systems
Howling noises at HVAC systems are often traced to
Howling at the Furnace Blower Traced to Wiring SNAFU
The following reader Q&A was originally posted as a FAQ at BUILDING NOISE DIAGNOSIS & CURE
Question: howling at a Coleman downdraft natural gas furnace - no A/C - but blows cold air
30 January 2015 Bill G said:
As you say the noise has to do with the air handler blower assembly (not the burner) I'd look for a failing bearing on the blower assembly or its motor or if it's a belt driven unit I'd look for loose or damaged belts or pulleys. Of course also look for collapsing air filters, duct crimps, holes, leaks that might sound or not sound like howling depending on air velocity.
My current guess..which may be off the wall is a possible motor control issue?? These AC motors are pulse sync controlled and if the control board is sending a bad bad sync pulse it may give this type result...maybee...?
Okay DJ.. we are fixed!
Excellent, Bill. I'll add your comments to this article series and elsewhere as it may help others.
I'd think about checking for
Reader Question: howling residential gas boiler traced to dirt in the system ?
(Jan 4, 2015) Jackson said:
I have a residential gas boiler heating system that is not just whining, it's howling. It actually sounds like there are three or more howls going on at the same time and the noise is even throughout the house. The circulation pump appears to be running fine and the heat exchange is not cracked/broken. Any suggestions?
Start right at the boiler: if the noise is at or in the boiler I'd shut if off immediately as it may be unsafe.
If the nose is coming from piping check for a failing circulator pump motor.
At HOWLING NOISES in BUILDINGS we include additional examples of howling sounds traced to heating or cooling equipment.
(Jan 6, 2015) Anonymous said:
Inspected the boiler again and decided to drain the water out to check how dirty it might be but it came out clear. Can't see any reason that it would howl. Put it together and howling has stopped. ?
I can only guess - which is mere arm-waving: that sometimes draining a system will move a bit of debris or dirt, changing an orifice through which water was running. I'd still be looking at circulators; also see if there's a correlation between howling at the boiler (other than you with laughter at this advice) and temperature or boiler on or off time or boiler pressure. Other howl points might be check valves, zone valves, even air bleeders or piping elbows.
or wa-wa-wa sounds or wow wow wow sounds or Huffing & Puffing Sounds: examples, diagnosis, repair advice
Question: Thanks for posting this -- it's been helpful to read! My question: The fan runs fine on our AC unit, but the compressor makes a slow, thrummy, WuwWuwWuw sound about every 30 seconds, as if it's trying to start up but can't, and there's no cold air coming out of our vents. I'm not sure if this is the same as the "humming" described above. Is it possible that this is caused by a loose connection or faulty capacitor? Or should I assume that it's something more serious? - Tiny
Question: Ours has a different sound outside: a sort of huffing and puffing. We only hear it after the unit has been running for a long time. Any ideas? - Herbert Lewis
Question: I saw the q&a about the wow-wow-wow sound but no answer other than tell us what you found. I have had it since it was installed but the heat pump tech said it was normal. I know it was not but gave up. Now it's bothering me more. Any new/better answers? The wow cycle period is about one second - in radar search antennas we used to call it "hunting." (for the right speed). There it had to do with control feedback settings, but somehow that doesn't translate to a heat pump unless it means too much coolant. Could that be it? - Dick, 3/11/2012
Reply: Huffing Puffing wawa or wowwow A/C Units - still and open question, how to investigate
Herbert: huffing and puffing is a new one to me: an air conditioner compressor making this noise might be reaching an overpressure condition due to a control failure or blockage - let us know what your HVAC tech diagnoses - it will surely help other readers
Sometimes the wowwow sound is from a compressor that is hard-starting. In that case you are hearing the electric motor trying to start against head pressure (or against a binding internal part), perhaps cycling on and off.
Dick, thanks for the question. We're very serious about developing a dictionary of sounds and their diagnosis and cure; but sometimes, especially by text, I just don't quite know what a sound is or even quite what it sounds like. The wowwow is one of those I'm unsure about in that there are several causes and several sounds that people describe as wowwow wawa. But in this FAQ (just above and continued below) we include some possible explanations and will add others as they crop up.
An on-site an expert might observe something cycling (as you describe) that helps track down the problem. For example, if you used a mechanic's stethoscope and tracked the sound to a specific part that is emitting the sound (probably a compressor or maybe a thermostatic expansion valve, on occasion a fan motor or bearing) then once we know where the sound is coming from, we can dig into what might cause that part to do that. For example a part on a system may be making a sound not because that part is itself defective but due to another control.
The sound is LOUD and must be from the compressor itself and passed along via the tubing.. The compressor is outside on the ground level and it is distracting on the floor above (beach house on stilts).
Here are some added steps to take to track down a sound to its exact source - a first step in diagnosing sounds
Pick up a mechanic's stethoscope (at your local auto supply store).
Go to the piece of equipment, air handler indoors, compressor/condenser unit outdoors, and listen to be sure you're in the right area.
Use the rod in the stethoscope to track the sound to a specific part that is emitting the sound (probably a compressor or maybe a thermostatic expansion valve, on occasion a fan motor or bearing.
Watch out: there are electrocution shock hazards and cut-off finger hazards or other injury hazards from moving parts and live electrical contacts. While the equipment has to be running if we're going to track down a sound to its emitting part, this process should be performed with great care and by someone with experience to avoid the chances of a serious injury.
Then once we know where the sound is coming from, we can dig into what might cause that part to do that. For example a part on a system may be making a sound not because that part is itself defective but due to another control.
Reply: Hard Starting A/C and Heat Pump Compressors May Make Groans, Wuw, and WaWa or Wah-Wah-Wah- Sounds
Tiny, it sounds as if your A/C compressor is indeed having trouble starting; It makes sense to be sure all wiring connections are secure (Watch out for electrocution shock hazards) but I suspect you need a hard-start/run capacitor kit. I would leave the system OFF until it is repaired. And keep in mind that a hard-starting compressor may be at/near end of its life.
Thanks so much for that input. I've been trying to decide whether it's worth having someone come out to check the capacitor, and it sounds like it might be. I'm not really prepared to pay to replace the compressor or the whole unit this summer, especially since I'm up in Canada, so the A/C is more like a luxury than a necessity. Thanks again! - Tiny
Reply: check for bad start capacitor;
I think it's worth checking for a bad start/run capacitor because if that's the problem it's an inexpensive part and avoids someone selling you a compressor condenser unit that you probably didn't need. Also a bad motor winding can cause similar complaints.
I have a 13 year old Armstrong AC, 4 ton, 10 S.E.E.R. in our house. For the past 5 years (ever since we got into the house), the outdoor compressor unit has been making loud humming sound. The sound does not sound like humming if I stand next to the compressor unit outside.
However, inside the house, the sound is of humming. The AC has worked fine - no leaks, cools properly etc. I have had it serviced but every time the service person chalks the noise to age and recommended a new AC w/o any investigation. It could be just age but I'd welcome suggestions things I can check for myself.
I followed the two lines (thin copper line and the larger/covered in black line) running between outdoor and indoor AC units. If I put my ear next to the larger line, I can clearly hear the humming sound along its length as I move from the outdoor AC unit to the indoor condenser unit. I can also feel vibrations/tremors on this larger line.
I have been hearing a humming when my air conditioner is running now for about a week but the air is cool and working o.k. but this is coming from the compressor outside and wondered what it could be??? - Joyce Ballard
There is a humming noise coming from the Heat Pump AC unit when the thermostat is in the cool setting, but the thermostat is set below room temperature (air conditioner not running). If I move the switch on the thermostat to the off position the humming stops in the unit. Do you have any idea what is wrong? Thanks, Don 6/3/12
Hi, I live on the second floor of a condo and hear a loud constant low pitched humming noise coming from inside the wall where the tubing enters the unit from the outside and travels up the wall and across the ceiling to the internal blower. The sound is not present when the heat is on. It is a deep harmonic mmmm sound and has a vibration component. The AC blows cold and otherwise seems to be working. The compressor is 10 years old. - Barbara Rich 4/9/12
Reply: Pinning down the exact humming noise source on HVAC equipment: refrigerant line noise transmission, loose component parts, low voltage transformers, and hard starting -electric motors
A humming noise that you are hearing at the larger refrigerant line (the suction or "low pressure" line) can help you trace the noise to its source: the indoor air handler or the outdoor compressor-condenser. Knowing the source can help track down a detail that may or may not be repairable, such as a loose part, loose compressor mount, or worn out compressor internal parts.
Watch out: a humming noise coming from an electric motor or A/C - Heat Pump compressor motor that is not actually starting and running is likely to indicate that the motor is unable to start, and is at risk of overheating or damage. Humming from a motor that can't start is sometimes repaired by replacing a bad start/run capacitor, but if the motor is actually failing and seizing, it will need replacement.
Sources of humming sounds from HVAC systems are outlined at HUMMING sounds from A/C or Heat Pump system
which usually leads diagnosticians to COMPRESSOR CONDENSER NOISE
and in that article at our description of ELECTRIC MOTOR HUMMING.
In the most expensive case we're looking at a BURNED-OUT COMPRESSOR
Often the problem is a bad start capacitor. (CAPACITORS for HARD STARTING MOTORS )
Aside: humming on oil fired heating equipment may be a normal sound transmitted to the building via oil piping attachment points. A/C refrigerant piping may also transmit equipment noises if it is not properly routed and mounted.
Question: Condenser not working, humming sounds
My a/c condenser is not working, the fan blades do not turn, when I lower the indoor thermostat and then go out doors to the condenser pad, I hear " a humming click" approximately every twenty seconds or so, as if the unit is trying to turn on.
Reply: humming indicating hard-starting or frozen compressor motor
Hilary it sounds as if you are describing a hard-starting or stuck compressor motor. The click you hear may be the the result of the system turning itself off (unable to start) followed by a cool-down interval, and then the system tries again. You need a diagnostic service call and if in luck it could be a a bad start capacitor. Out of luck, a shot compressor. Other problems can also cause the compressor to have trouble starting, such as a bad refrigerant control valve.
Reply: Rattling, followed by Low Humming Noises and hard starting compressors
Kim: that humming sound makes me think your compressor is either suffering hard starting or is at end of life and close to seizing.
Continue reading at HVAC NOISE Group 4 - loud start up noises, popping, rattling, rumbling, running water or select a topic from the More Reading links shown below.
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