Screaming Singing Squealing HVAC Noise FAQs

Q&A on Air Conditioner / Heat Pump Compressor, Air Handler, Ductwork
Screaming, singing, squealing, trumpet noises
Group 5 HVAC noise FAQs

FAQs on Scream, Sing, Squeal, Siren Noises at HVAC Equipment

High pitched squealing noise at the AC Condenser/Compressor motor

Outside AC unit, regular split system. It's been running fine, but not cooling as well as it should. Today, the fan came on on the condenser, but the compressor did not and it began making a high pitched squealing noise . We shut down the unit and the squealing continued for another ten minutes. What is it? - On 2019-05-15 by Chelsea

Reply by (mod) -

Usually squealing noises at compressor/condenser unit start up tell us that a motor is unable to run, either in the condenser unit fan or on occasion in the compressor motor itself.

The service tech will see which motor isn't starting and might recommend either a hard start motor capacitor (a temporary fix that might give some additional life to the unit) or a motor replacement.

For more detail, take a look at the AC Compressor squealing comments at

https://inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions_5.php#Squeal

Watch out: Some units have a high pressure safety valve. It sounds as if the fan was not working and the compressor was overheating.

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

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? - Hiya

Reply:

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

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. - Courtney said:

Reply:

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.

Loud Squeal from Central A/C - needed a new fan motor

I just experienced that loud squeal from my central A/C system.

Two or three years ago, the compressor of our old, 25 or so year old, system failed during a heat wave. I couldn't get anyone to do anything with it for "at least a couple of weeks," so I looked at alternatives.

All the service people told me that a new outdoor unit would have required a new indoor unit, but the ductwork is already undersized, so I'd really need a whole new installation - a couple of months to schedule and install, which was not happy news as the temperatures were in the 90s during the day and 80s at night with high humidity.

Long story short, I found a replacement compressor on-line and after talking to the vendor, selected one that replaced the one I had. I flushed the system with an approved cleaner, purged with nitrogen, and brazed the lines with the recommended material using new refrigeration copper fittings

. I pulled a vacuum on the system for 6 hours and then tested that it would hold 30". No leaks. The system has been working fine since then and the charge is correct as per the manufacturer's reheat chart (no TXV).

I just started to notice a periodic loud squeal from the outdoor unit that last less than a minute or so. I know the head pressures are high because the discharge air temperature from the condensing unit is unusually warm. Once the squeal stops, the condensors air discharge temp from the fan is noticeable cooler -- about normal for this unit.

Now what? Vacuum the system? Purge it? Install a filter? I have no idea what my next step is, but it's been working well, so I'd like to keep it that way.
I'm probably going to have to call someone in as this is a bit outside of my experience. - Thank you!!

...

The condensing unit fan was stopping and then starting again. When stopped, the head pressures went too high and the compressor screeched.

Then, for whatever reason, the fan would start turning again, and as the condenser cooled and the pressure reduced, the noise lessened.

A new fan motor solved the problem. - On 2016-08-30 by fc3 -

Duct damper open caused squealing noise

I went to a customer's house and found one of the dampner was slightly opening a little bit and then closing making a noticeable sound in the master vent because of the air getting by slightly.

Does this mean the Dampner is bad or can I tighten it some how? This is in residential home with three zones - On 2017-07-02 by Thomas -

Reply by (mod) -

Thomas,

Assuming that we are talking about an HVAC Zone dampener, you may need to disassemble it to find the loose part.

Or example the central baffle may be loose on an arm that holds it in position inside of the duct.

If there is a complaint about air noise passing the damper, which is possible since the damper will not be perfectly airtight, it may be possible to adjust it's stopping position just enough to change the opening size to eliminate the noise.

Siren or wowwow sound at the compressor

What would make what I call a beat frequency sound (nearest thing I can describe it with is the European police sirens that go up and down in frequency, like dee doo dee doo).

The time period is around 1-2 seconds for the beat frequency. I had a ceiling fan that did the same thing. Maybe it's the motor? On 2016-12-10 by Barry -

Reply by (mod) - wowwow sound is from a compressor that is hard-starting

Barry

Barry, I'm not sure but some possibilities are in the article above at

WaWa, Wow wow sounds from A/C or heat pump system, diagnosis

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.

See https://inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions_3.php#Huff

Quick scream at A/C unit start, like a small child who saw an insect.

Brand new noise. It is a quick scream at start like a small child who saw an insect. Lasts about 3 seconds at start. Is this related to humidity or 40-50 degree temperatures (ie, bearings or belt)?

Unit runs often because thermostat is inaccurate (yes, that is going to be replaced - a builder spec Honeywell that came with the house in 2006).

a/c is original unit. I rarely run heat above 20 degrees outdoors (townhouse is too well insulated, will hit 70 degrees inside when it is 32 outside with no heat operational, which I hate. I'm a 62 degrees woman all year round) - On 2016-11-23 by Katy -

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?

L.M.

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.

Follow-Up:

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

Reply:

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

Reply:

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.

More Screech, Shriek, Squeal, Whistle & Whine Noise at HVAC Equipment, FAQs

High pitched sound from freon line on my Payne air conditioner

I have a payne air conditioner. Very high pitch coming from freon line. Guys that came said psi is normal - On 2019-08-03 by Wendy weimer

Reply by (mod) -

Wendy

often the noise we hear at a refrigerant line is being mechanically transmitted from an HVAC motor or component nearby.

It's also possible that a refrigerant line is partly blocked or a refrigerant metering valve is malfunctioning

also

In the CONTINUE READING or RECOMMENDED ARTICLES see these two diagnostic start points for a high -itched whine or noise in HVAC systems

HVAC NOISE-3 HISS HOWL HUFF HUM - hiss, howl, huff, hum, groan, woo wuu wuff

HVAC NOISE-5 SCREAM SING TRUMPET WHINE WUWU - scream, sing, squeal, trumpet, wawa,

Furnace makes faint noise like tornado warning sirens

First of warm season, my basement furnace unit makes a faint noise like tornado warning sirens in the distance when running. The ring stops when I remove filter cover panel. What the heck? On 2018-05-12 by Jon

Reply by (mod) - air leak or air filter noise?

Jon

that sounds to me like there's an air leak either in the duct work or air handler or simply around the air filter itself.

See HVAC NOISE-5 SCREAM SING TRUMPET WHINE WUWU - scream, sing, squeal, trumpet, wawa, wowo, water gurgle, whine, whistle, wuwu

On 2020-01-26 by Stan - Squealing noise at Mitsubishi Split System

I have a Mitsubishi split duct system. Originally the upstairs unit only blew warm air. The downstairs unit workef fine. Repair man couldn't find the problem just added a little refrigerant. Than in the heat mode ,neither unit worked. When I put it in heat mode it would make a squeeling noise.

Repair man was here again, different company. He was on the phone with Mitsubishi and they went through the diagnosis together. Every test checked ok. Finally they said there might be a restriction in the line some where.

They recommended replacement of the whole system. I believe this can be fixed by someone who has experience in these units. This unit is 11 years old , but downstairs ac worked fine until first repair man looked at it and added a little refrigerant. They want $9,000 to replace the whole system. HELP!

On 2020-01-26 - by (mod) -

Stan,

Disappointing - "replace the whole system" might make sense if the technicians knew that the failure was a part so costly to replace that the repair approaches the cost of a whole new system - and on an 11 year old system that might be true; maybe a bad compressor in a hard-to-access location. But how do we know that.

When I was in refrigeration school we learned that most of the failures in refrigeration equipment were in the controls and switches.

So every spring when everyone in Dutchess County NY put their old "no-good" refrigerators out on the highway to be carted off as junk, a few enterprising HVACR techs would drive around in pickup trucks picking up the better-looking refrigerators, bring them into the shop, fix the bad defrost timer or door switch or thermostat, and then re-sell the perfectly good refrigerator.

So while neither of us is as smart as Mitsubishi technical support nor as your service tech, before spending $9000. I'd want to know more about what's really wrong.

To me this smells like an OPM problem: spending Other People's Money makes your (the tech's) job both easier and more-profitable, and it doesn't cost you (the person saying "let's just replace it all") a dime.

OTHER PEOPLE's MONEY is at
https://inspectapedia.com/home_inspection/Other_Peoples_Money.php

A squealing noise often means a failed compressor; there are certainly tests such as measuring current draw, that can diagnose that; but something as simple as a stuck reversing valve or defective thermostatic expansion valve can also prevent an A/C or heat pump system from working.

Squealing coming from our new A/C unit

I had a new unit installed in April. Still cool here that time of year so we were using heat. When it warmed up and we turned the ac on, we started hearing a loud pitch squeal. It only happens late at night/early morning. Typically between 1 and 6 am. It happens in between cycles.

Not directly before or after startup. It comes from the component that's in my crawl space (I'm not too sure what it's called).

I've tried different things to try to get it to stop and have figured out that it only squeals when the thermostat is set higher than the outside temp or close to the outside temp. In other words I have to have it set much colder than the temp drops at night.

For example, I have it set to 68 starting at 9pm.

Last night the temps dropped to 67. Woke up to it squealing this morning.

The installer cannot figure out what it is. He replaced the brand new blower motor thinking that's what it was. Didn't help at all. Any ideas? It's about to drive us crazy! - On 2018-09-23 by BJ -

Reply by (mod) -

if your technician has ruled out all mechanical noise sources such as those that might be related to a blower fan or it's driving Parts, another thing to check would be the thermostatic expansion valve

When the air handler fan is on a high pitched whine comes into our bedroom

A new Lennox air handler system installed yesterday. When the fan is on, a high pitched whining noise comes through the bedroom only.

Taking out the filter stops the noise. Filter is supposed to be 18" by 24" and that's what's in there. But there is quite a bit of space between the edges of the filter and the channel it fits in.

My earlier air handler, also Lennox, was very quiet except one time when the filter collapsed and the whining sound came back, only in the one duct.

Replaced the filter and everything was good. Installation company is not sure what the problem is. Any clues? On 2014-09-13 by J Smith -

Reply by (mod) -

J S

Since the noise is just in one area I don' think this is the fan unit itself; try looking for a return duct air leak

Followup by JS - why would the whining stop when I changed the filter

I will, but why would the whining stop when I changed the filter in the previous air handler?

Reply by (mod) -

Anon re whining ductwork

Dirty air filters reduce air flow, creating more negative pressure in the return duct, thus possibly increasing noise at duct leaks.

OR the noise is actually originating at air leaks around the air filter itself.

My ac unit makes a squeal or whistle.

My ac unit makes a squeal or whistle.

I will hear the fan motor turn on fine and then right before fan blower up in roof turns on it will make the noise and then also right before turn off.

Don't know what it is. I just bought this brand new unit 4 mo ago and its never made this noise before. On 2013-04-03 by sarah

Reply by (mod) - My ac unit makes a squeal or whistle

Sarah squealing compressors are discussed e at Squealing air conditioner and heat pump equipment, diagnosis

HVAC NOISE-5 SCREAM SING TRUMPET WHINE WUWU - scream, sing, squeal, trumpet, wawa, wowo, water gurge, whine, whistle, wuwu

Loud screeching noise from air conditioner

Just had my ac fan motor replaced 2 days ago. System ran fine since then. This morning I heard the system kick on and heard a screeching sound from the compressor. I went outside to see the fan trying to spin. I shut the system off, waited 10 minutes and turned it back on. The compressor fan was spinning but was making a EXTREMELY LOUD SCREECHING sound so I turned if off. What could this be??

Just had my ac fan motor replaced 2 days ago. The system was running great since then. This morning the system kicked on and the compressor was making a screeching sound, so I went out side to see the fan 'trying to spin'.

I shut the system off, waited 10 minutes then put it back on.

The fan was spinning but it was making a EXTREMELY loud screeching noise, so I shut the system off. What could it be? On 2012-09-11 by mrr2ro - On 2012-07-18 by Debi -

Reply by (mod) -

Debi,

The causes and repairs for screeching and squealing are described at HVAC NOISE-5 SCREAM SING TRUMPET WHINE WUWU - scream, sing, squeal, trumpet, wawa, wowo, water gurge, whine, whistle, wuwu

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.

There is also "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.

On 2020-07-26 by Rick - Whining noise at hospital HVAC system

I live near a hospital which has a very large HVAC system in the rear parking lot and this system makes a very consistent and very loud noise 24 hours per day, 7 days per week.

The noise very similar to a sine wave although if examined on an oscilloscope it would certainly have distortion.

The pitch is approximately 492 Hz. I have searched all over the internet for an explanation of what causes this noise but have been unable to find an answer. Can anyone help explain what is causing this noise?

On 2020-07-26 by (mod)

It's not uncommon for a fan or bearing or motor to whine, Rick; to find the exact component that's the noise source the service tech might need to try

- selective shut down of equipment to see what stops the noise

- use of a mechanic's stethoscope

On 2020-01-16 by Samantha - Magic Pak HVAC unit making a faint but persistent high-pitched noise.

The Magic Pak HVAC unit in my apartment has been making a faint but persistent high-pitched noise. The noise is not rhythmic, it's steady. The noise is present whether the heat or AC is running. I'm looking for help with finding the cause of this noise and fixing it.

It started earlier this winter. When I first noticed the noise, the unit was having an issue where it kept switching off unexpectedly/failing to turn on.

The repair guy replaced the fan - he said there was an electrical issue inside the fan which was causing a safety mechanism to stop the unit from running. Replacing the fan made the unit "run fine" - it switched off and on when I wanted it to.
A few days later, the unit failed again in the same way.

The repair guy changed the pressure switch. This fixed the unit, and the problematic noise went away.
But the problematic noise returned in a few days.

When the repair guy returned for a third time, and when he took the pressure switch out and put it back in, it made the noise go away for maybe a day or so. But now it's back and we are out of ideas about how to fix this noise.

The unit is technically running "fine" but I need help diagnosing and fixing the noise. It is not a normal noise for this unit, which I have had for years. The noise seems to be getting worse the longer I try to run it. The noise is also painful to me (I have sensitive hearing and it is causing me pain).

I need to get this problem fixed as soon as possible. This has proven difficult - so far, the technicians have dismissed the problem because the unit technically runs.

Other relevant info: I live in an area with cold winters - temps have stayed between about 0-35 this the winter.

On 2020-01-16 by (mod)

Samantha

The fact that the noise occurs in both heating and cooling mode needs detailing:

In heat mode is heat being provided by a heat pump - same basic machine that provides cooling - or by a separate electric, gas or oil furnace?

On 2020-01-20 by Samantha

This is very helpful, thank you so much for pointing me in the right direction. I do think you are correct that the burner is running in heat mode, as I recall that the flame was going out when it was -20 during the polar vortex last year.

One question - did you mean to write "you're not using the compressor unit in heating mode"? I thought the compressor was typically used in AC units, so I'm a bit confused by that part.

Samantha said:

- great question. I don't know, but here is the unit

Download from this website:

MAGICPAK PACKAGED HVAC UNIT MGE4 SPECS [PDF] (2018) at inspectapedia.com or contact MagicPak, 215 Metropolitan Drive | West Columbia, SC 29170
800-448-5872 Product Support 866-282-7257 retrieved 2020/01/17 original source: www.magic-pak.com/MagicPak/literature/technical-specifications/M-Series_MGE4_Tech_Spec.pdf

Moderator reply:

Samantha yours is an packaged HVAC system combining an electric cooling unit with a gas heating unit split system.

IF you are hearing a high pitched noise independent of whether the system is in heating or cooling mode AND if the gas burner is running in heat mode (thus you're not using the compressor unit in cooling mode) THEN I’d suspect

- a fan bearing failure

- an air leak

- something else we’ve not thought-of

A service tech can usually spot the problem, often by using a mechanic’s sthethoscope to identify exactly which component is producing the high pitched sound you’ve identified.

On 2020-01-20 by (mod) - Magic Pak HVAC persistent high-pitched noise.

Right; keep in mind I'm flying blind when I'm not sure what equipment you actually have.

Cooling mode: uses an outdoor compressor/condenser unit;
Some outdoor compressor/condensers are heat pumps; those can provide both heat and cooling, while a straight cooling-only unit just does that.

I think your unit is the latter.