Photograph of an old burned-out air conditioning compressor unit HVAC Noise Descriptions & Recordings - Group 5
Air Conditioner / Heat Pump Compressor, Air Handler, Ductwork screaming, singing, squealing, trumpet, water gurgling, whine, whistling, wuwuwu noise

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Diagnose these HVAC noises:

Screaming, singing, squealing, trumpeting, water gurgling, whining, whistling, wuwuwu sounds at an air conditioner or heat pump.

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.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

HVAC Noise Diagnosis of screaming, singing, squealing, trumpet, water gurgling, whine, whistling, wuwuwu sounds

Photograph of  This new compressor was placed directly against
a brick wall. One third of its condenser coil cooling ability was blocked.Article Contents

Screaming HVAC compressor/condenser unit noise & warnings

Watch out: turn off electrical power to the screaming A/C Condenser / Compressor unit immediately. It may be unsafe to continue to operate.

Common causes of loud screaming sounds at an air conditioner or heat pump compressor/condenser unit

Loud screaming noises at the compressor unit may also be described as a high pitched compressor noise, compressor whining, compressor screaming, or bearing noise.

Since some people describe these sounds as hissing rather than screaming, also see HISSING SOUNDS, HVAC

Other Sources of Screaming (high pitched whine or whistle) Sounds from HVAC Equipment

With power off check for play in the blower fan assembly. Sometimes we temporarily confirm a bad bearing by putting a drop of oil right into the bearing assembly. If the noise stops we've identified the parts that need replacement.

Examples of field reports of hissing noises from A/C and heat pump systems are found at our FAQs section below.

Question: screaming jet engine noise from the heat pump or A/C condenser/compressor unit

(June 12, 2015) Hiya said:
When the compressor kicks on, our office's large commercial A/C unit sounds like a jet engine, and it had gotten progressively worse over time. Is this normal?



Above we include some common causes of screaming sounds from air conditioners and heat pumps.

For more examples of possible causes of screaming and jet engine soundfs you can use the

link NOISES, HVAC SOUND DESCRIPTIONS - home - you'll see an index to A/C noises that includes howling that may give a clue about what's going on with your system -

or see HOWLING HVAC sound noises.

Question: high pitched screaming heat pump

(Feb 18, 2014) Courtney said:

My heather [sic] [heat pump?] recently began making a low high pitch screaming sound the entire time the heat is blowing, it piercing and started to hurt my ears. I also noticed it made a loud bang just before the heather kicks on. Should I be worried?

I also forgot to put that it makes a tick tick tick sound for about 10 seconds before it kicks on at all. Im sure its an old model i live in a very low rent if that says anything apartment.


Sounds like a compressor having trouble starting. The noises you describe don't sound very safe. I understand it's cold but it would be safer to leave the equipment off while waiting for a service call.

Silence: No Noise, Silent or Soundless HVAC Compressor or Fan Unit

Silent or normal noise A/C Compressor - still to be replaced?

My AC is blowing warm air. Everything is in working order except the technician found a leak from one of the tubes coming out of compressor closer to the unit itself. He told me that the whole compressor would have to be changed. Is it true? The compressor sounds normal. - Ehab

Reply:blowing warm air ... lost refrigerant; I answered this question just a minute ago - maybe on our refrigerant gauges page?

Ask him/her why you need a new compressor instead of a fix of the refrigerant leak and either a recharge, or if your refrigerant is an obsolete R12 or R22, why not use a substitute refrigerant?Note that a compressor may sound normal or even close to silent but be running but may not be pumping refrigerant.

If this is the case the unit has broken internal parts and needs replacement.

A symptom would be no refrigerant pressure difference between high side and los side lines even with the compressor "running".

Singing or rumbling compressor/condenser unit noises

Sounds like a whining, singing or rumbling sound coming from the compressor/condenser unit fan motor may be due to a broken internal cooling fan motor part or a vibration set up between the fan blade and fan motor/shaft.

Squealing A/C or Heat Pump Compressors: examples, diagnosis, repair

Reader Question: loud squealing, clanking compressor noise

Above: we provide a video of noisy squealing clanking A/C compressor - condenser unit - 6 Sept 2013

This brief video contributed by one of our readers (L.M.) demonstrates start-up troubles and loud continuous squealing, clanking, and what I take to be some humming at the outdoor fan-compressor unit. The unit is unable to start and run normally.

A/C Compressor Noise Description:

Twice in the last month in a half, we’ve had this squealing metallic noise coming from the exterior condenser. 

On both occasions the AC was running fine all day, then about 930 or 10 PM it starts making this noise.  In both cases it eventually stopped making the noises on its own.  It makes the noise only while AC is running.  Fan only is OK.

Some guesses at what the noise means are given below.

Other videos: VIDEO GUIDES at

Sources of squealing noises at an air conditioner or heat pump compressor



Because I couldn't see clearly in the photo and there was some intermittent clanging, I first thought to check for a fan blade assembly that is hitting an obstruction, is loose on its drive shaft, wobbling, hitting the enclosure.

But your note that the noise is intermittent argues against a loose part or assembly.

But ultimately, to me this sounds to me like a unit that is unable to start. I suspect a bad compressor motor or bearing.

That cyclic sort of clanging-buzzing sound may be a motor or fan motor trying to start in response to a start relay; the continuous squealing though sounds like a bad motor.

I speculate that during the day the compressor is running continuously in hot weather, perhaps also making the motor itself quite hot.

Then finally in the evening as temperatures fall, the compressor and centeral A/C gets ahead of the building cooling load enough to cycle off - but not for long. Trying then to re-start fairly quickly the motor may be unable to re-start against a remaining high refrigerant head-pressure.

Such troubles can be caused by a failing compressor motor, an improper refrigerant charge (less likely), a sticking refrigerant control valve (possible), or something else I haven't thought of.

It's time for a service call by an experienced HVAC tech.

Let us know what your service tech reports - what we learn will assist other readers.

Also see RUMBLING NOISES A/C compressor/condenser or blower fan motor noise

Reader Question on squealing A/C outdoor compressor/condenser Unit

Our compressor started squealing intermittently the other night around 1:30am. Did it for about 2 hours but not consistently nor constantly. drove us and the dogs crazy. hasn't done it since. HVAC tech says it was the compressor bearings and can't fix it since its 20 year old unit. I think that's love. what do you say? - Secn

Reply: normal air conditioner compressor squeals?


Normal vs abnormal squealing sounds at A/C compressors (Secn said: ... "that's love"... is that a new term for B. S. Turns out Secn meant "leak" but his spell checker thought otherwise. )

Anyway, there are multiple possible sources of squealing, such as the compressor motor, or even a fan motor. If it's the compressor, it's dead or dying; because the units are hermetically sealed, they're not repairable.

BUT ... as we cited in the article above "Normal air conditioner compressor squealing: Some compressors emit a high pitched noise during normal operation or just at startup. This noise should be brief and just at start-up, and will probably have always been present on the system if it's normal."

In your case it the compressor never squealed before and is noisy now, it's less likely to be "normal" and more likely to mean the unit is nearing end of life.

Your choices may be to install a hard-start capacitor to try to keep it going as long as possible, figuring soon it'll need replacement, or to go ahead and replace it now to reduce the risk of being days without A/C during hot weather.

I'd be inclined to limp along until the end of cooling season if possible - the A/C techs will be less busy then.


Thanks Dan. yep, wonderful spell check changed from the word I had originally typed to "love". it was a clean word though but B. S. works just as well. hah aha.

So, the tech also said it's drawing high amps along with the bad compressor. Would the cap fix this too? He said he can't service anything on it Cruz it is R22 freon and can't be obtained anymore. I know they are moving to the R410a but I still say B. S. - Secn


Sorry Secn but high amps draw means the motor is near end of life. The cap may keep it going a while but it sounds like it's bad news. Tech is also right about the refrigerant.

You may be able to install a new compressor, evacuating and cleaning the system (better to do it BEFORE a compressor burnup as a burnup contaminates the piping and increases the later repair cost a bit), installing a new compressor and a substitute refrigerant, possibly having to make some other adjustments, but less costly than a wholesale replacement. Keep us posted. - DJF

Reader Question: hard starting A/C compressor, squealing noises, high pressures: diagnosis & repair

Hello and thank you in advance for any assistance you can provide. My house central air conditioner began to make squealing nosies upon start up so we had a professional repair company come inspect it. It would still start, eventually, after turning itself off and on several timnes, and the cooling still worked great.

The first inspector said he checked coils (they were dirty and my husband cleaned them), capcity, contactor, etc.

This person put on a hard start kit, and went away. Well, the problem was still there and in fact worse. We called again, and the company sent someone else who checked more areas and filled up the freon and went away.

Well, it was still starting very hard, with noises, and my husband removed the hard start.

He began to check the voltage and wires and borrowed a pressure guage from a good friend who does this for a living. We thought is might be the high pressure shut off switch, but when we started it again last night with the guages on, the high pressue shot up for about a minute and then slowly came down and settled within its stated range.

We sat by the outside unit watching it the entire time of course to shut it off at the switch outside if needed.

Again, cooled just fine, but now we have seemed to eliminate the high pressure switch as being bad and we don't know what else to try. Our friend said he has never heard of a unti starting with such high pressure and then settling back down with no issues.

We are of course trying to avoid replacing this unit. It is a YORK, 12 years old, and installed by the builder when we bought this house new.

It is a 5 ton unit as we have a dual zone system, which just means it has a damper in the attic unit that directs the flow from one side of the house to the other. Do you have any thoughts on what else to check, what to do, or do we just throw in the towel and buy a new unit? - T & L A, 7/11/2013


Some of this AC squealing and high pressure diagnosis you've gone thorugh is indeed a bit confusing; squealing compressor noise is not likely to be fixed by cleaning the coils - it's more like doing what one knows how to do regardless of the problem.

Typically a squeal means hard-starting which could be a bad compressor motor, bad start capacitor, or a compressor having trouble starting against a head pressure (try leaving the system off for 30 minutes and then re-starting). Similarly, just "adding freon" is not going to fix the problem - "to a carpenter every problem looks like a nail"

Watch out: I would NOT be messing with pressure checks even though you have a gauge; the problem is that without connecting the gauge set to a can of refrigerant and purging the gauge hoses and fittings you risk introducing air into the A/C sytem and messing up its charge or worse, introducing contaminants.

You may be uncomfortable being candid, but you should certainly tell the HVAC tech what you've done so far, so that nobody rules out a messed-up or contaiminated refrigerant charge. Otherwise people could waste still more time and money by not guessing the complete history of the system.

Installing a hard start kit is the first line of attack many techs use as it's quick, easy, inexpensive. When that does not work, a more careful inspection and test of the unit controls, charge, voltage draw during startup, and similar steps are needed for an accurate diagnosis.

I suggest calling your HVAC service company, talk calmly and without accusation (or they'll just go into defense mode) with the service manager, and ask him to send a senior, experienced technician out to test and diagnose your system.

Also see the article beginning at the top of this page for some discussion about A/C noises and


Whoosing Sounds at HVAC Equipment: causes of periodic whoosing noises on heat pump systems

Whistling Noise at HVAC Equipment: diagnose whistling at the air handler or compressor/condenser or in Ductwork

Whistling sounds in HVAC duct work or air handlers are often due to air leaks see

Whistling Thermostatic Expansion Valves (TEVs): on refrigeration systems that include a liquid refrigerant receiver and as long as there is adequate level of refrigerant in the system and the TEV is working, the refrigerant charge amount is not absolutely critical.

But on any refrigeration system, receiver or no, if the refrigerant charge gets too low (there is a refrigerant leak somewhere) then refrigerant gas cycles up through the TEV rather than liquid refrigerant. The result is that the TEV will begin to run "wide open" and it will often make a loud whistling sound.

A whistling TEV means low refrigerant. (You won't hear whistling at a capillary tube metering device).

Listen for a whistling thermostatic expansion valve - a sign of low refrigerant and if you hear that whistling sound


Reader Question: whistling squealing window air conditioner [recording provided]

8/28/2014 I have a window/wall air conditioner that recently started making this very annoying "squealing" sound. It doesn't happen all the time though... In fact, it almost seems to trigger when something else happens (e.g. when the walls rattle or vibrate, or when a door closes, etc) although sometimes it just kind of happens.

The unit is actually mounted in the wall on a chassis and when the noise is active, it's pretty loud inside the house but it's almost non-existent if you're standing outside next to the compressor. The only way I can get it to stop squealing is to smack it on the side a few times, but even with that it still starts to squeal again (at one point or another).

WHISTLING WINDOW AIR CONDITIONER is a recording I made of the sound in case that helps.

Any help / advice is most appreciated. Also, because I rent the place I'm kind of at the mercy of the landlord (which is why I haven't just replaced it myself).


Jeremy a window AC compressor motor that's squealing - if the sound is indeed coming from the motor - would most likely have the same causes as the squealing noises in the article above.

"Typically a squeal means hard-starting which could be a bad compressor motor, bad start capacitor, or a compressor having trouble starting against a head pressure (try leaving the system off for 30 minutes and then re-starting)."

On some air conditioners the noise you describe could on occasion also be traced on occasion to a bad thermostatic expansion valve. The fact that the noise stops when you smack the unit could point in that direction.

I'll post your recording HERE [link to .m4a noise recording] to encourage other hvac techs to comment further.

9/1/2014 Thanks for the response, mod.

A little update. I made a video to try and give you a little better idea of what's going on, because I believe the squeal is coming from the air handler/blower fan.

Also, while my camera was inside the top of the unit I noticed a buildup of water at the bottom and then realized that normally the unit drips water on the outside but I haven't seen water dripping in quite a while (about a month).

Assuming the squeal is coming from rust on the shaft between the blower and the partition, and that the rust is coming from the water that would normally drip onto the ground, is there anything I can do to fix it? Or even make it so it drains the water again? I have a feeling that even if I'm somehow able to fix it, the standing water will just cause it rust over again (assuming that's the problem, of course).

Video can be seen here: jeremy [dot] ws/ac [dot] php

Jeremy's shrill high pitched SCREAMING WINDOW AIR CONDITIONER RECORDING recorded from his video [3.6MB sound file]


I think you're right, Jeremy - in that I see the blower cage assembly is wobbling like mad. Perhaps there's a failed bearing in the squirrel cage fan. Turn off the system, remove power, and see if you can wobble the fan assembly on its shaft.

I added links to a sound recording from your system, and if you can email me the video or provide a download link I could add it here for other expert HVAC folks to comment upon.

Wow Wow WaWa or WuW sounds from an A/C or heat pump system

Please also see GROANING, HUFFING, WUWUWUsounds from A/C or heat pump system, diagnosis where we discuss these noise descriptions together.


(June 11, 2015) Odd wahwahwah noise said:
I am a new condo owner. The other day I turned on my AC and left it on auto. It worked fine, no unusual noises. Then last night I decided to turn off the AC and open up the windows. My AC unit is located outside in a cabinet on the porch. My bedroom is upstairs.

While I was laying in bed trying to get to sleep I heard a very loud wahwahwah noise,I knew my AC was off but it sounded like a fan or compressor on.

I went to see if air was coming out of the vents and it wasnt. I confirmed both of the thermostats were turned off. I could hear the wahwahwah throughout the house.

After 15 minutes it stopped. then it started up 5 minutes later.[Wah Wah Wah noise from the A/C unit] this cycle continued and continued and i was baffled and agitated. Finally, i decided to go turn on my ac, so i did. I let the air blow through the vents for a minute or so then turned it off. the sound NEVER came back.

I dont know what this could be since the unti was OFF, but after i started it up again and then turned it back off it appeared to resolve the issue. Now I'm worried to even turn the AC on again. I do have a home warranty and its only a $60 service call to have someone come out, but has anyone heard of this issue?


Sure Odd. In the HVAC noise links above see NOISES, HVAC SYSTEM DIAGNOSIS - home and you'll see several categories of noise descriptions including GROANING, HUFFING, WUWUWU the one you name.

Question: whistling AC at time of turn off

(May 19, 2014) Anonymous said:

My a/c unit is making a high pitched whistling noise when the unit goes off. Any ideas?




we discuss whistling that is often traced to air leaks in the duct system. Let me know if that's your case.


Continue reading at NOISES, HVAC SOUND RECORDINGS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see HVAC NOISE-5 SCREAM SING TRUMPET WHINE WUWU FAQs - questions and answers posted originally on this page

Or see these

HVAC Noise Diagnosis Articles

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