HVAC Noise Diagnosis & Cure FAQs

Cooling or heating system noises

HVAC Buzzing Noise FAQs

Reader Question: loud buzzing noise from compressor unit

I had problems with my central unit freezing up and dripping water on my fan motor.. decided to have a technician change out my coil inside.. when he left my central unit outside starting making noises i never heard before.

My air conditioner kicks on inside first then after a couple of minutes it tries to kick on outside , it makes a loud noise then it runs finally and quiet like a central unit should run outside.. what is causing this all of a sudden, never had problems until he changed my coils out..not calling him back to my house. Bruce McCann

Reply:

HVAC compressor buzzing video: the HVAC noise diagnosis introduction near the top of NOISES, HVAC SOUND DESCRIPTIONS includes a video example of brief buzzing at the fan/compressor outdoor unit along with some possible explanations. Below we discuss several A/C or heat pump compressor noise observations and possible explanations.

Bruce, I am not clear on why a coil freeze-up indoors would lead to changing the outside coil - maybe low refrigerant or improper high side vs low side pressures? In any case, I would indeed give the service tech a call, tell him or her what you are observing, and give the technician an opportunity to return, see what's wrong, and fix it.

Most technicians want their work to be correct and successful. Let us know what you're told - it will surely help other readers.

Bypass bad circuit breaker to fix a buzzing noise?

LIcensed tech came out yesterday to repair A/C. Fixed problem.

Today handler is making a loud buzzing noise. (He cleared the drain and bypassed breaker that he said was not needed. He said the breaker was bad, but he bypassed it, as it was not needed or required by local codes.) Now a tech won't come back until Monday.

Is it safe to keep running unit? We raised the thermostat so that it does not run as much.
Thank you! On 2018-09-28 by Carmen -

Reply by (mod) - do not bypass the circuit breaker - risk fire or shock

Carmen

Watch out: Bypassing a circuit breaker could be risking an electrical fire or shock injury. I would turn the system off and ask for a proper repair.

The buzzing may just be a bad relay in the A/C, and I realize that the breaker the tech bypassed could have been simply a service shutoff next tot he A/C equipment.

But bypassing ANY circuit breaker makes me worry that the wiring (aluminum for example) or breaker, or controls are unsafe - and dangerous.

Buzzing from furnace fan compartment, fuse blows

40 y/o Payne furnace: after burners come on, buzzing sound from fan compartment for 20-30 sec. and then burners go off; on/off furnace switch fuse blows - (Apr 2, 2014) Sandor Lipschultz

Reply: check for a bad relay or contactor used to control HVAC motors

Buzzing is often a bad relay switch. Sounds as if there may be a failed motor or control.

An overcurrent when a motor can't start-up can aksi be the cause of blown fuses.

Occasionaly I also find buzzing at the low-voltage thermostat.

You need a service call from an experienced HVAC technician.

For safety, leave the system off. If the weather is cold right now, call for emergency service.

Question: what the attached air conditioner buzzing clanking sound recording means?

Attached is a few seconds of the noise made by our Kenmore air conditioner/heat pump, when the propellers start turning, about 10 seconds into the recording. It was much worse in the winter with the heat pump, so we heated with oil only.

It was so bad, the house rattled inside. The compressor and motor were replaced a few months ago, but the noise persisted and the maintenance company gave up after eight visits. When the weather got hot, we decided to give the air conditioner a try.

The air conditioner was working without us noticing any noise but now we can hear it, as you can tell from the recording. What can we do? Your help would be greatly appreciated. - L.G.

Recording of Kenmore Air Conditioner Noise  - buzz, rattle, hard-start

Reply:

Honestly, I'm not sure, but the sound we heard in your recording sounded like a mix of buzzing and rattling. I've heard sounds similar to this from both a failing crankshaft in a motor and from an air conditioner compressor that was liquid slugged with refrigerant due either to an improper charge or a malfunctioning refrigerant metering device.

If that's right we may be hearing a hard-starting compressor.

I have two suggestions: a technician, using a mechanic's stethoscope, ought to be able to pinpoint this noise to the offending part or motor. If the noise is traced to the compressor motor I suspect my guess above is not far off. It is possible that once the system has been running for enough time the noise may fade as the compressor has pushed the refrigerant out to the high side of the system.

Watch out: liquid refrigerant slugging of a compressor motor is a problem that occurs on the low pressure side of the system where the equipment is designed only to move refrigerant as a gas, not a liquid - liquid slugging of refrigerant at the compressor motor is likely to destroy it.

See REFRIGERANT FLOODBACK, LIQUID SLUGGING

I hope you've already eliminated more obvious external rattles such as a bad bearing or motor shaft or fan blade ticking against screen or internal component.

At RECORDINGS of A/C or heat pump sounds & noises we have introduced a new HVAC diagnostic feature (thanks to you) where we posted this air conditioner sound recording to permit other readers or experts to offer comments.

Mouse-damaged components caused banging noise at the compressor

Had service technician yesterday since we heard a loud banging noise the night before from the compressor. When he took the outside casing off to inspect, there was evidence of mice nesting inside. The nesting was cleaned out and a loose wire was fixed.

Unit operated normally the rest of the day and again that night the loud noise was heard.

The technician returned the next day and replaced the contactor that he said was loose and partially burned on one side. Again, unit operated normally entire day and noise was heard again tonight. What could be happening? On 2018-08-23 by Brian -

Reply by (mod) -

Good going for the tech to find and fix the mouse damaged components in your compressor/condenser unit.

But yes there can be other causes of banging noises. Assuming the banging is at the compressor/condenser unit, see BANGING A/C or heat pump
found at
https://inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions.php#Bang

Loud Buzzing fromn A/C electrical box

The AC voltage box in the attic is making a loud humming or buzzing always. What could cause that? - 2017-12-04 by Ava

Reply by (mod) - electrical problems that could be causing buzzing

Ava

there are a number of possible electrical problems that could be causing buzzing in an electrical box, including these examples (this isn't an exhaustive list)

• a bad electrical connection that is arcing
• a failing electrical component such as a relay
• a failing circuit breaker
  
  I can't guess at exactly what's happening in your case because I don't have any information at all about what electrical equipment is present.
  
  Watch out: However it's very important to avoid a possible electrical fire or even building fire that you turn that equipment off at the electrical panel and call a service technician or licensed electrician for repair.

See also ELECTRICAL SYSTEM NOISES where we give more examples of buzzing noises that are electrical in origin.

Question: heat pump buzzing due to motor mounts?

The heat pump, outside unit, is mounted on steel brackets. It buzzes constantly when running. Could this have anything to do with it's mount?

Also, right before it cuts off, it makes a louder buzzing noise and then stops.

The noise is affecting my life! It makes me feel ill due to the vibration. - (Nov 29, 2015) Margaret

Reply:

Yes loose condenser unit mounts can be a source of buzzing.

HVAC makes loud buzzing noise for 10 minutes same time every day

Hello! I have an HVAC that at the same time every day makes a loud buzzing noise that make sure the house vibrate, and lasts for exactly 10 minutes.

This has been happening since we purchased the house almost a year ago. It is an 18 year old unit on the roof, and we have had service professionals come and look and they find nothing wrong.

They looked at the unit while the buzzing wasn't happening however as it only happens at night and early morning and they won't make calls then. We have a nest thermostat and thought that was the culprit, and so we dismantled it but the unit still went off.

We live in Southern California and it happens regardless of temperature, and regardless of whether the unit is blowing heat/air. We turned the power to the unit off one night and it didnt go off. Another night we turned the power off while it was happening and the sound continued! Any advice would be appreciated! On 2017-03-18 by Lisa hartman -

Reply by (mod) -

Lisa:

Do look through the buzzing noise sources in the article NOISES, HVAC SOUND DESCRIPTIONS

Or see NOISES, HVAC SYSTEM DIAGNOSIS - home if you haven't done so already.

If the problem has been there for some time that may make it easier to find - but of course it's tough for your techs to diagnose if the noise doesn't occur when they're there.

Certainly a thermostat won't itself cause noises, though improper switching of a compressor/condenser on and off could be trouble - such as turning a system off and then turning it back on immediately - a compressor can have trouble starting against the high pressure that remains in the unit for a few minutes or more after it's first turned off.

If the noise is really regular in occurrence and duration I'd ask the tech to consider that information:

- cooler night time temperatures

- timers that are turinng the sytsem on and off

- something else in the building or at the site that is time or clock driven

Buzzing noise at Carrier Performance Series A/C unit Model # 38TXA060350

I have a Carrier Performance Series A/C unit Model # 38TXA060350. During the cooling cycle, when the compressor kicks in, there is a buzzing noise coming from the compressor and continues until the cooling cycle ends.

If the noise was just outside it would not be such a problem, however, the noise follows the lines into and thru our basement and is very irksome. What is the problem, the solution, and is there a way to mitegate the noise?

thanks,
jim On 2012-07-14 by jim -

Reply by (mod) -

Jim, take a look at the text near the top of this article and you'll find a live link to buzzing noise diagnosis cure;

Buzzing sounds (also crackling) at electrical components anywhere, including compressor relay switches, electrical connections at any component, and quite seriously, at circuit breakers can be an indication of arcing and an electrical problem needing prompt attention. See Electrical System Noises

Air Handler Makes Buzzing Noise when Heat is Turned On

My indoor A/C handler is making a loud buzzing noise when the heat is turned on, the noise starts as soon as the heat kicks on and ends when the heat kicks off.

I'm pretty sure my system has a heat strip if that helps.

What should I be looking for if I remove the front plate of the handler to take a look inside? - On 2017-12-12 by Bryan W.

On 2017-12-13 by (mod) - buzzing noise repair

Bryan,

Please take a look at the description of a common sources of buzzing noises at

HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing

That would be the best place to start

Rooftop ac/heater is making buzzing noise

My rooftop ac/heater is making buzzing noise. I read several of these articles and they do not seem to match my situation. I have a payne unit. The noise seems to be coming from the compressor coils, even when all power is secured. It will buzz for 4 or 5 seconds, and stop. This happens on and off randomly.

The noise is not at the compressor, but the upper copper coils. I dont suspect any leaks because the air conditioner does work great otherwise, and if there was some sort of leak the unit would not be working anymore.

The noise does not have any thing to do with contactors or motors, or capacitors. I have replaced all of those, and they all work.

The noise does not come from those parts anyway, and the noise should not be present when there is no power. This gets annoying when I go on roof to wash down my solar panels. On 2014-11-26 by Mark

Reply by (mod) -

Mark I agree you want this buzzing diagnosed but I'm unclear from your note just what might be going on.

1. are you saying the buzzing happens when power is off?

2. you are sure buzzing is not from any of the electrical components - I'd look again as relays often are a buzzing noise source as are failing motors. A loose electrical connection can also be a noise source as well as dangerous.

3. Check motor mounts and all other mechanical fastners. Try pressing on the exterior of the access panel or door or cover when the equipment is buzzing.

4. Check for a bad fan bearing

Question: Buzzing sounds from air conditioner

My outside fan motor is running but the unit makes a loud buzzing noise every few minutes or so, the motor was replaced last spring.

I sprayed the motor shaft with wd40 just to get me by till I can get another fan motor if that is needed. I do not know if the capacitor was replaced or not. the loud buzz only lasts for a few seconds then stops, I just turned the unit back on, Any ideas on what I can do or a place to find a motor?- Rodney Looney

Compressor started producing a buzzer noise which lasted about 4 seconds then stopped and repeated again. The time between buzzes varied from a 10 to 20 seconds. The noise reminded me of the sound you hear on the radio when they do there check of the emergency broadcast system. - Jim

I have a Trane 4 ton gas pack that is making a intermittent buzzing noise when the compressor operates.

We are located in Phoenix, AZ and the noise seems to have started this season when temps heated to 100 and above.

Naturally, I'm concerned that this might be compressor noise since the unit was manufactured and installed before the AC season in 1994. Thanks for any suggestions you can offer. Doug

More info:
The unit is on the roof of a flat roof house and the noise is most noticeable when standing below the unit.

The noise is a higher frequency buzzing that could be a panel or other object vibrating close to the frequency of the compressor.

To my knowledge, I have not been on the roof when the noise occurred, or if it did, I didn't hear it with all the other noise. It seems to occur at various combinations of temperatures.

Under some conditions, there is no noise, but other times, such as during a long run when we lower the temp after the sun sets, the noise may start several minutes into the cycle. A few times, I noticed noise soon after starting that only lasted for 20 seconds or so.

We run the indoor temps between 85+ and 81 over a 24 hr period using a programmable thermostat.

I have banged and thumped on the case, removed the outdoor fan grill and looked for loose fasteners within the compressor/condenser portion of the case and checked all of the fasteners on the outside of the case to make sure they were tight. I put card-stock shims between joints of panels, etc to prevent any vibration that might occur.

So far, nothing has eliminated the noise that seems to occur only under certain combinations of outdoor/indoor conditions.

The noise pattern may be different from when I first noticed it. I checked the pressures, for the first time since we got the house 8 years ago and and added 4 lbs of R-22 to get it back to normal operating conditions at 95F.

The performance isn't noticeably different, but the noise pattern may have changed somewhat, while the sound is about the same, when it does occur.

Last winter I removed the top of the unit to oil the indoor fan motor. That is the first time it has been removed since we owned the house. As far as I know, everything was reassembled correctly.

My experience is limited to light to medium maintenance of only my own auto/home AC systems for the past 4 decades.

I installed a quick start system about 5 years ago on general principals because one worked wonders on similar but smaller gaspack in another part of the house. - Doug

Reply: Buzzing Sounds at an A/C or Heat Pump System May Mean Failing Electrical Parts

Rodney: if you need a new condenser fan motor you should be able to match the original by taking the old one to your local HVAC supplier, or you can probably find a replacement online. I'd be sure you note the motor information and specs from it's data tags or just bring in the old motor to your supplier.

Watch out - don't keep replacing motors unnecessarily. A bad fan motor contactor relay or even a loose wire could also cause buzzing in the condenser/compressor unit outdoors. .

Jim: sounds like your compressor is having trouble starting up? Or does it buzz but run ok otherwise?

Doug,

buzzing sounds from an air conditioning component might be a failing electrical component and could involve even a fire risk; I'd try to track down more carefully where the buzzing is occurring. A burned compressor contactor relay, for example, might buzz.

Noise diagnosis is tricky in part because there is some subjectivity in how people describe sounds (buzzing vs humming for example). Taking care to not get whacked by a moving part like a compressor fan, one can sometimes use a mechanic's stethoscope to get right to the source of a sound from mechanical equipment.

Follow up:

Dan,
Thanks for your suggestions. I'm relieved that you didn't point to the compressor as a typical source for noise like mine, but I know I can't rule it out yet. I took a dowel rod up to listen to for any noises, but at 94 deg, it didn't make any abnormal sounds (my wife confirms).

I did notice that the top of the condensor at one edge was vibrating and a potential source of noise. I'll check it later. I opened the control compartment and all seemed normal and no loose components there.

I would like to be able to listen to the compressor, but there's no way without dueling with the outdoor fan and I would likely lose. I'll let you know if I ever come to any conclusions.

Follow up:

Dan,
A while ago, I wrote about intermittent noise from my roof mounted gas pack. After spending a lot of time on the roof and poking around inside the compressor compartment, I am reasonably certain the noise is coming from the compressor itself. I checked the compressor mounts and they are solid and there are no loose parts to vibrate and cause noise.

In the process of pushing the compressor around to see if the mounts were loose, I heard the compressor hit the side of the shell.

I was looking around another site and the owner mentioned that the compressor suspension mechanism can break and cause noise that sounds like a bad bearing.

A friend of mine knows a person in the refrigeration business and after my friend described the problem, he said it sounded like a broken spring in the compressor suspension.

I guess I am going to have to replace the compressor before the start of the next season, if I make it through this one.
Hopefully I will replace it before there is a burnout.

Would you recommend installing a filter/dryer even if there is no hard failure? I don't believe Trane installs them in new-build units and there is certainly none in the compressor bay. If the compressor banging against the shell is releasing particles into the system, is there a filter or something other than a dryer that will catch the particles?

The compressor has rotolock connections, and I would like to avoid any cutting/sweating operation if I can reasonably-safely avoid it. Thanks for your help. - Doug

Reply:

Doug:
re: noise is coming from the compressor itself - a failing compressor motor indeed can become noisy;
I would not install a filter/dryer before replacing the compressor because

• an extra cycle of opening the refrigerant piping system risks contamination and also done properly requires vacuuming and cleaning the whole system
• it's a bit of a costly procedure to do at that point
• when the compressor is replaced a filter/dryer would normally be installed as part of the job

But if you wait for a failing compressor to burn up the result can be extra contamination in the refrigeration system.

For those reasons I'd ask for an experienced HVAC tech to look at the system, diagnose the problem, and then I'd decide if it were time and better to replace the unit now, or shut the system down and replace it before start of next season.

Follow-Up:

Mod:
Thanks for the tips. All makes sense to me. I will consult with the a dealer that I know, before I do anything. I am inclined to just replace the compressor though, if I can find one at a reasonable cost. I found a new AM Std compressor on eBay that appears to be interchangeable with the one in my unit, but so far, I can't find cross reference data that I trust.

I will probably use it lightly until we get into cooler weather (6 weeks)and hope for the best, but prepared to replace the whole unit if crashes. I'll add a filter/dryer if I replace the compressor. Sorry if I didn't make it clear, I wasn't thinking of a two step operation.

I found a video on You Tube that shows disassembly of a compressor like mine. I don't think there is a broken suspension, but I would believe bearing noise. I don't understand how it can be so intermittent. Under certain conditions, something resonates and makes a real racket.
Thanks again for the help. - Doug

Mod:
Regarding installation of a filter/dryer; the filters I have seen on HVAC parts sites are for installation on the suction side. When I installed an AC in my house in '88, I installed a filter/dryer in the liquid line, near the coil as recommended at the time.

It seems to me that it makes more sense to filter the liquid entering the TXV than to filter the gas entering the compressor. What am I missing? I purchased the compressor on eBay. It turns out that it was exactly the P/N specified in the parts list for the equipment. The gaspack contained what I assume was an earlier equivalent part. - Doug

Reply:

Doug we see filter dryers installed at both sides of the compressor. It depends ... if a system is thought to be contaminated there are advantages of having a filter at both ends of the compressor motor, and it certainly doesn't hurt. - DF

Question: A/C System Buzzing noises for 2 seconds, bad start/run capacitor?

Outdoor unit makes a buzzing noise for about 2 seconds & stops. Fan never starts turning. I was standing by unit when this happened for the third time & manually started fan turning.
Fan started running on its on, but at a very low speed, nothing like it normally does. Any suggestions? Inside unit seems to work normally. - Hill

We seem to have traced this A/C buzzing noise to a bad start/run capacitor - Hill

Question: buzzing carrier AC unit goes BONK BUZZZ then runs "fine"

(Sept 3, 2015) Christopher said:
I live in an apartment complex and we have these really small CARRIER units from 1997. Our Apt complex told me " well if they're blowing cold were not gonna replace them. "

I just noticed tonight sitting here with no TV on nothing on around me when the outside unit kicks on I hear a loud and it kinda sounds harsh BUZZZZ like Electricity telling it to come on. Like right now it just went BONK BUZZZZ..... other than that its a very loud system but matience said oh thats because its a very old AC system.

We have been having alot of brown outs in this town and people have had stuff fried left and right I am wondering what that BONG BUZZZZZ noise is? Is it just the electricity hitting the fan motor and thats the fan coming on?

Thanks,
Christopher

Chris@cmarlow.info

Reply:

Sounds like a failing relay or control in the unit. I suspect repair or replacement is in the near future.

(Sept 3, 2015) Christopher said:
Dan:

(13 hours ago) (mod) said:

Sounds like a failing relay or control in the unit. I suspect repair or replacement is in the near future.

Was that answer for me?

Was going to also say... After it goes BONK BUZZZZZ it runs fine..

Thanks,
Christopher

chris@cmarlow.info

Reply: yes.

Buzz when heat pump tries to start

Great information here, thanks. I have an older heat pump that was working well, then stopped. I get a buzz when it tries to start. I hear the buzz at the breaker and at the unit, but cannot tell you where it originates.

Very short, then nothing. I think it is the unit quickly realizing it did not start and bailing. It does not trip the breaker. I replaced the run capacitor, which changed nothing. I replaced it again, to make sure the replacement was not bad. No difference.

It is clean, well maintained, but might be tired. After reading the information on this site, I wonder if I might want to try a hard start kit. Or should I accept that it is time for a new unit? I want to make sure that I have managed to get the most out of this unit. Any feedback would be appreciated, as I must have a working unit before summer. Thank you. On 2020-01-16 by e -

Reply by (mod) - banging, bearings, buzzing, thumping, vibrating sounds from AC

e:

at HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing, thumping, vibrating sounds

above on this page you may have seen our list of common sources of buzzing sounds

But when you're hearing the noise at the circuit breaker I'm worried that there is a bad electrical connection and arcing - that can cause overheating and a failure or in the case of aluminum wiring, possibly a buillding fire.

Hearing the buzz at the condenser unit is more common and usually is a relay buzzing when a motor is unable to start or on occasion a failing relay itself.

A hard start kit (start capacitor) is usually one of the first things a service tech will try because it's inexpensive and somewhat diagnostic in that if it gets the system running you figure it's a failing compressor motor (or if you were lucky, just a bad start capacitor)

Watch out: if you're not familiar with safe electrical wiring you could be shocked or killed - I'd prefer to keep our compliment-prone readers alive.

On 2020-01-16 by e

Thank you for your reply! Love this place. I like doing these things myself because I learn so much, but I do have a VERY healthy respect for the deadly power of electricity. That being said...

I took a closer look at the wiring. There is no aluminum wiring anywhere around here, except to the residence from the power company. POWER OFF. I noticed some green corrosion on the ground wire to the compressor. Had to cut it back about 4" to get to clean wire under the insulation.

Put a new spade on and wired up. Looks better, but same issue. And a new issue! All in the name of learning. The blower motor will not turn off. Just from cleaning up the ground wire on the compressor? Yeah, I am scratching my head.

I have no idea what is going on with that, but if it gives you any clues... Also, I am not too worried about that, because it is an easier fix, and if I cannot get the compressor to work, it is irrelevant. I am going to give the hard start kit a shot at this point, unless you think this new symptom is the unit gently singing a goodbye song.

On 2020-01-17 by (mod) -

If you can do so without getting your fingers chopped off from a moving fan blade, try a mechanics stethoscope to see if you can pinpoint the component that is making the buzzing sound. That would be the most useful diagnostic.

Loud sporadic buzzing noise from Fjjitsu Halcyon DC Inverter (Wall Unit)

Hello, I have a Fujitsu Halcyon DC inverter (wall unit) that is making a loud sporadic buzzing noise.

It sounds electrical in nature to me, like a transformer or maybe something short circuiting. There are four indoor units running off one outdoor unit. Only one of the indoor units is making this noise.

The system is new, only six months old, in a new house.

The unit will make this noise even when it is powered off.

I can't figure out a pattern to it, sometimes I'll hear it several times in an hour, sometimes I won't hear it for a couple of hours. The installers were here and of course it didn't make the noise until after they left.

They were telling me there's basically nothing in the unit that could cause such a noise and suggested that it was that maybe just a grill rattling or the sound of refrigerant flowing through the pipes but I don't believe that, it's far too loud and besides it happens when the unit is powered off.

They are coming back Friday and I would love to tell them what to look for. Thanks very much!
Joe Greaney
jfgreaney@gmail.com - On 2016-09-21

Reply by (mod) - Buzzing when electrical power is off - what to look for

Buzzing when electrical power is off:

No insects, right? NO animals or animal nest, right?

I'm puzzled too. Even if we had an odd problem such as a late-releasing torqued motor component, refrigerant, relief valve, or fan motor, the sound ought to occur once, not repeatedly.

And refrigerant doesn't keep flowing through pipes when a unit is off. Certainly not several times an hour.

Wind over loose components?

Sound from other nearby sources?

I would look for:

1. low refrigerant charge or a refrigerant metering device (TEV thermostatic expansion valve) problem causing freeze-up of the system; later thaw-out might be permitting some refrigerant flow. (The TEV will usually be inside at the cooling coil).

2. Confirm that the noise occurs when power is OFF to the compressor motor. That ought to eliminate a failing compresor motor and also loose condenser unit parts such as a grille, motor or unit isolation feet, mounting, piping supports, failing contactor relays, bad fan motor, or other loose parts. That should also eliminate noises traced to improper voltage such as too-low voltage and a motor unable to start.

3. Try covering the unit or cooling it off with fine spray from a garden hose, simulating rain on the unit. Does cooling the system change the noise?

4. Inspect the electrical wiring to the unit including the condition of the outdoor service switch, circuit breaker, wiring for a bad buzzing connection - an unsafe electrical fire hazard.

5. If your unit is a heat pump then check the solenoid coil switch that operates the reversing valve on your system - really ask your service tech to make these checks. For some heat pump systems the reversing valve solenoid may buzz for a time when the system stops operating - pressures are equalizing. It's normal.

Outside air conditioner or heat pump is making funny buzzing sounds

My outside heat pump is buzzing and the fan is not running - (Mar 7, 2015) jr

HVAC contactor does loud short buzz about every minute. I heard this yesterday and replaced the contactor and it is still happening. Could this involve the 24VAC from the thermostat, or capacitor, or something else? - (June 6, 2015) Dale

A/C is turned off and if I turn power on outside its a whining or buzzing sound in the house. the a/c is not on inside or turned on. but the sound is coming from the air handler area. have to turn power off out side to a/c to stop noise. - (July 8, 2015) Nelson

A month ago I replaced the condenser fan motor & capacitor. Now the entire outside unit is shaking so bad when the fan is running that it cracked the cage. And, it is making alot of noise & not cooling again. Any idea what it may be? - (July 28, 2015) Benny

Reply:

Examples of condenser unit buzzing noise sources for these descriptions include:

Bent fan blades,
Worn or damaged fan bearings
Bent fan drive shaft
Loose fan mounts
Burned out compressor motor unable to start

Watch out: Do not keep running this unit; it will be further damaged and it is unsafe.

 

Buzzing rooftop condenser unit in Florida

Above my condo are 3 large condensers that service a restaurant on the ground floor of the building. I can hear 2 of them come on and off.

One has a nearly continuous buzz / hummm sound, the other one has more of a motor sound, almost like a small plane that wants to take off. This is summer in Florida, so they are on virtually all of the time.

Builder tells me that due to hurricane code they must be mounted directly on the roof. *they are over my bed room! Is there any help for this? thank you - yOn 2016-07-07 by Mary Hale

Reply by (mod)

Mary,
Start with your local building department about location requirements.

Even direct rooftop mounting does not prohibit sound isolation methods.

Also from your description the equipment may not be working properly and may fail soon.

A/C unit is making a loud buzzing sound when starting up

My outdoor A/C unit is making a loud buzzing sound when starting up, so I contacted a tech to take a look at it. The day he came ended up being very cool and when we turned the temp down to get the A/C to turn on it didn't really make the sound.

He checked the pressure on the unit and determined that it was very low on refrigerant.

He assumed that there must be a tiny leak in the system that had allowed the refrigerant to get this low over the years (the unit is 20 years old and uses R22).

He charged the system back up with R22 and also fully examined it. He could not find the leak, and he did not see anything else wrong with my setup, so the hope was that recharging it would solve the problem in the short term.

The thinking was that if it took 20 years to get low on refrigerant that the unit would eventually die before the new charged refrigerant leaks too low to cause new problems.

On the next hot/humid day the system started up but it made the same sound: the fan starts up and it seems to be spinning normally, then the compressor starts up and I feel that is what is making the buzzing sound, the buzzing eventually stops, and the unit runs normally.

Despite the buzzing sound the unit is continuing to work properly. Any insight to what is going wrong would be helpful. After spending so much money to get the R22 recharged, I'd like to extend the life of my system as long as possible.

Here is a link to a video showing the problem, the sound can be heard about 10 seconds in.
https://drive.google.com/open?id=0B7U0HSdbkoVCYWxaVno3MDFKdms - On 2018-06-13 by Sid Thunder

Reply by (mod) - where to start when the A/C unit is making a loud buzzing sound when starting up

Sid,

Please take a look at the common buzzing noise causes given in HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing

Did your tech say why low refrigerant would cause buzzing?

Followup by Sid Thunder

I don't remember exactly, but I think it may have been the thought that the compressor was being overworked due to low refrigerant.

I will take a look at the common buzzing noise article. Did my audio/video help confirm or deny my suspicion that it is a problem with the compressor?

Reply by (mod) - video of buzzing compressor

The buzz in your video starts when the compressor and fan turn on - apparently from the compressor motor though from the video I couldn't be certain;

if it's the compressor, the problem could be a hard-starting compressor motor - low refrigerant alone would not cause this issue.

Followup by Sid Thunder

As far as hard-starting, the capacitor in the system was replaced and a hard start kit was also installed. My lights don't flicker anymore when the A/C kicks on, but the buzzing sound is still there.

As a test, I will disconnect the fan to try and determine for sure if the buzzing is coming from the fan or the compressor.

If it is in fact the compressor, is there anything else that could be contributing to a hard start condition besides the capacitor?

Reply by (mod) -

Could be a buzzing relay

see HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing, thumping

HVAC Banging Noise FAQs

Why is our central air conditioner/heater making smoke and a loud noise?

Why would smoke and loud noise be coming from central heat/air unit - On 2015-01-12 by Bonnie

Reply by (mod) -

Watch out: A fire or electrical components overheating and burning up: SHUT THE SYSTEM OFF IMMEDIATELY.

If you can't safely do so at the equipment's local shut-off power switches do so from the main electrical panel.

If smoke and noises continue you'll need to get out of the building and call your fire department.

If they stop then you can call your air conditioner repair service.

Cannon Boom! when copper refrigerant line "exploded" on my heat pump

Had a copper line "explode" on my heat pump last night. Sounded like a cannon going off. What might have caused this and what is the fix? - (Jan 1, 2016) Rich

Reply:

Rich:

Watch out: I trust you have turned OFF the system completely, both for safety and to avoid further damage.

If I assume that you are referring to a high pressure-side refigerant piping line that has burst, I suspect that a refrigerant metering device such as a TEV (thermostatic expansion valve) became jammed or clogged, the compressor kept pumping away, an excessively high head pressure developed, and the particular system did not include a high pressure limit switch (as is often not present on residential systems).

What caused a loud explosion sound from my heat/air unit outside

I heard a loud explosion sound from my heat/air unit outside. now it will not come on at all - On 2014-09-16 by Anonymous

Reply by (mod) -

Sounds like your AC system blew a fuse, circuit breaker, compressor motor or other component.

Watch out: Leave the power OFF completely to the system and call an HVAC technician for repairs.

Diagnosie causes of BANG sound at compressors

Our outside HVAC compressor makes one bang sound when it shuts down. The sound is like someone would hit it once with a steel hammer. On 2019-06-06 by Darrel J. Hebert -

Reply by (mod)

Darrel

Let's start with the diagnostic suggestions at

HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing, thumping, vibrating sounds

Let me know what you find and we'll continue from there.

Banging sounds from the compressor

OK. I just reread the instructions and it looks like I can ask a question. In the past 5 years we have replaced 4 compressors. We just replaced the last one and the fan motor. Every once in a while, the unit would make a repeated really loud banging sound as though some metal piece in the fan was whacking another piece over and over. Today I watched the clock

It is almost at every hour, but not at the same time. Each time the noise lasts 3-4 minutes. The A/C company and their electrician have no clue what this is. Also, the unit often trips the circuit breaker. Not necessarily when this noise comes on. We are incredibly frustrated. Any ideas as what could be causing this? Thank you. - Dina

Reply: common sources of loud BANG noises in air conditioning or heat pump equipment

Dina, my OPINION is that if you are replacing compressors 4 times in 5 years something is drastically wrong. I can't guess whether the problem is an innate system design pressure, poor or damaged equipment being installed, or installation errors.

But I share your frustration. I think it's time to talk candidly (but without threats or screaming) with the A/C company's service manager and to ask that they send someone who is trained and experienced to help diagnose this problem. And when you're told what problem was diagnosed, if you don't understand the explanation, ask for more help with understanding it until it makes sense.

A fan whacking something is a loose fan blade or broken fan shaft or bent screening around the fan or a stick or junk in the unit - any of which is a serious problem for the fan. If your service tech left the system like that s/he did not do such a hot job.

A unit that trips the circuit breaker is probably drawing high current - which, if the proper breaker has been installed, points to a problem with the wiring or more often the compressor motor on that circuit. A failing compressor motor draws high amps.

I'd also suggest checking out the voltage being provided to the system to be sure that there is not a low-voltage problem from your power source.

Follow-Up:

Thank you so much. Here's the problem. We just changed service companies , because we were not satisfied that the old one was doing a good job. This one decided that the compressor and then the fan needed replacing. They've had two sets of technicians out here and neither could figure out the problem. There is nothing hitting the fan (so they say). The problem is that they are never here when the sound happens, though

I did record the sound for them. They said it was nothing like anything they've heard before. They are coming out this morning again and we will see what they can find. Thank you for your "opinion". - Dina

The tech was here again. He noticed that the last guy had installed a booster. He disconnected it to see if it helps. Meanwhile, I'm wondering if the noise has something to do with the unit working harder in the hot weather because I hadn't noticed the noise at all today and it's much more comfortable outside. I guess I won't know until it turns really hot again. - Dina

Even with the booster disconnected, it's still making that banging metal sound. - Dina

Reply:

Dina if the banging clanging is a compressor noise see the article

titled NOISES, COMPRESSOR CONDENSER

Banging Sound from Ductwork: furnace sucks in metal return air panels when it starts with a BANG!

I've installed a new 2 stage variable speed furnace in my basement, the air return is above it in one central register on the main floor about 30 x 12.

I have found that when the furnace starts it sucks in the metal air return panels in the basement that lead into the back of the furnace.

I added another heating vent to the system into the basement, but have not increaased the air return yet. I have also turned the down speed of the fan to the lowest it will go, so now it ramps up slower. those 2 items have helped a lot.

However I need as well to leave the front of the furnace door open for additional air, otherwise it still sucks in the metal return. I was told to put bracking inside the return, which is an option, another option I thought would be to add another return to the other side of the furnce with another opening and filter.

A furnace man came out and said that would work, but wanted some others ideas and opinions. Thank you in advance, email to cws56501@yahoo.com - curt

Reply: solutions for start-up / shut-down BANG noise at metal duct work or air handler panels

Curt,

I've seen and heard metal panel bangs, clunks, and thunks that can be a startling heating system noise easily traced to just what you observed. This loud BANG, described by some as a CLUNK or THUNK or even a WHOMP sound, can occur at both start-up and shut down of air handling heating and cooling systems.

See the diagnostic and repair suggestions

at BANGING NOISE at AIR HANDLERS or in DUCT SYSTEMS

Also see UNDERSIZED RETURN DUCTS

Question: banging noises from heat pump when heat is running

Ron said:
My Heat Pump makes a constant banging sound only when the Heat is running. The video shows the fan moving oddly... but to the naked eye it seems fine. Any ideas?

Here is a video of the "banging" hard-starting fan on this outdoor compressor/condenser unit.

Reply:

Ron

Ordinarily I'd say that to find the cause of ticking, rattling or banging at the fan component of a compressor/condenser you want to look for a loose fan bearing or bent blade or something obstructing the fan.

But after checking the video found in your banging compressor noise video (above) I see that the motor is having trouble starting and is cycling at start-up.

Possibly the the fan has a bad start/run capacitor. Try replacing that and let me know what happens.

See CAPACITORS for HARD STARTING MOTORS

Below is a video excerpt adapted from Ron's "banging compressor" sound video.

BANGING HARD-STARTING COMPRESSOR FAN MP4 file recording of banging noises at a hard-starting HVAC compressor/condenser unit.

 

Question: loud banging noises coming from our A/C unit and constant cut off of the air supply

I am frustrated as well with loud banging noises coming from our A/C unit and constant cut off of the air supply through the vents while the outside fan spins aimlessly.

We have had 2 service calls with 2 different technicians only to be told they could not tell the problem but charged us anyway for each service visit.

I even went so far as to record the banging sound on my phone. Please help!! my email is jasonericbillz@gmail.com - Sept 7, 2016) Jason B. said:

Reply:

I'd give the service manager a call and ask for a more-experienced technician.

Also be more specific about where the noise is occurring: outdoor unit, indoor air handler, ductwork.

Followup: Anonymous said:

Thanks for that response. the noise is coming from directly inside the main vent in the living room. That vent is located a few feet from the indoor unit located in the ceiling of the bathroom.

I have had 2 men look at the unit and still tell me and other tenants that the noise is the condenser coil making the noise and it only happens when the unit kicks on. That is true, but it is so loud that it can wake me up out of a deep sleep.

I can't believe that that is acceptable. Why would the condenser coil make that noise, and is it possible for the condenser coil to do that? I'm at a total loss.

Thanks for any further information you and/or others might be able to offer.

Reply: give the service manager a call at your HVACR repair company; politely explain the problem and ask for help from an experienced service technician.

Periodic BANG from my air conditioner keeps me from sleeping

I'm seeking professional help in desperation. I haven't slept for weeks because of odd HVAC noise in my apartment.

I live in a rental unit in NYC, as of March. The HVAC unit had been functioning perfectly with normal sounds using heat in the winter and a/c in the summer. Then suddenly around 8 weeks ago I started hearing a periodic BANG from the unit. It happens every 10-12 minutes, about 5 times an hour.

It's a very loud vibrating BANG, sounding like someone is hitting metal with their hand. I initially thought there was something wrong with my unit, but I tested it and found that even with my unit turned absolutely off, the sound would continue.

After much monitoring, I've found it occurs only in the wee hours (4, 5 am, continuining through to 7 or 8 am, possibly later although I leave for work.) It never occurs when I come home, when I turn on the A/C, for example (another argument it's not coming from my unit). It always begins and wakes me around 4 in the morning (hence the lack of sleep), and the cyclical nature is like psychological torture.

My building has not been able to track the source, and I'm thinking it must be the person above who keeps late hours, who comes in late and then maybe turns their unit on and eventually it causes some kind of popping in my unit below. I asked them to bring in a professional to resolve this as this is causing me emotional and physical strain.

Does anybody recognize what this sound might be, and what might be causing it? Thank you in advance. (Aug 26, 2015) Barrianne@gmail.com

Reply: banging that is not coming from the HVAC system? occurs at regular intervals.

Barrianne

From just your e-text I don't think we can make a reliable diagnosis of an HVAC noise source, though this article series including

NOISES, HVAC SOUND DESCRIPTIONS does describe some sources of banging sounds in A/C equipment. Don't forget to consider other noise sources such as banging water pipes. inspectapedia.com/plumbing/Water_Hammer.htm

Also expanding or contracting metal ductwork can make similar sounds.

Also see

HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing

BANGING A/C or heat pump

Loud banging noise at AirEase heat pump

I have a AirEase heat pump a/c unit in my attic for the 2nd floor zone. It is 6 years old.

Now that the seasons are changing and it’s getting colder at night my heat kicks on during the night, once it reaches desired temp the outdoor fan unit will turn off the indoor unit in my attic has a 90 second delay for all of the air in the ducts to be blown out before it shuts down.

After this happens about a min or so later I get a loud repetitive bang, bang bang bang bang Which sounds like it’s coming from the line set and back pressure of some sort. Does anyone know the cause or the fix for this banging.

It is loud enough to jolt you out of bed thinking someone is banging the door. And this is only happening during the night not during the day so it makes me think the outdoor low temp is a problem? On 2019-10-26 by Chad -

Reply by (mod) - diagnosing your banging heat pump

Chad

let's start diagnosing your banging heat pump at

BANGING A/C or heat pump

and continue at

BANGING NOISE at AIR HANDLERS or in DUCT SYSTEMS

and after you've been through those diagnostic suggestions don't hesitate to post follow-up comments, observations, questions, and we'll continue from there.

A/C unit makes banging noise, shuts off, can't re-start

My AC unit indoor will run for awhile then start making this banging noise even though it’s not cooled to desire temp yet. It’s like it shuts off and is trying to start back up. Unit is only 2 years old. Help! On 2018-08-09 by Allie

On 2018-08-10 by (mod) - air conditioner banging noises

Allie

Let's start with the diagnostic suggestions for air conditioner banging noises at

• BANGING A/C or heat pump
• BANGING NOISE at AIR HANDLERS or in DUCT SYSTEMS

Diagnose loud thunder noise or banging on our roof - coming from ceiling vents

Last evening I had the heat on when my husband got home cuz he works third shift he turned the heat off and put the air at 71 as we live in Florida

He went to bed about 4:30 this morning he said at 8:00 a.m. he was awoken as was my 10-year-old son by a very loud thunder like noise or like somebody was on the roof banging.

There was no thunder it was sunny out.

He said it was only in like our bedroom and our boys' bedroom which is located on the far right side of the house which is also where the outside unit is located.

He said he went outside there was nothing. The noise was basically coming from our ceiling and the vents that are up in our ceiling.

He turned off the air and the noise stopped.

He waited a few minutes and put the air back on and it hasn't made that noise since so we're curious as to what this could have been because the noise was so loud that it woke a couple people up.

They said that it sounded like there was really bad thunderstorm or someone was actually on a roof banging.

If anyone could possibly tell us what this might have been or could be please let us know as we're not very acquainted with these types of things with the HVAC systems thank you we appreciate it On 2020-11-26 by Angela -

Reply by (mod) - failing HVAC equipment

Angela

Thanks for the interesting AC/Heat pump noise question.

The compressor motor in some heat pumps or air conditioners (in the outside unit) can have trouble re-starting if switched "OFF" and then immediately back "ON" - because the motor is trying to start against a high head pressure of refrigerant.

Newer equipment often includes a safety control that simply prevents re-starting right away but older equipment may not have that feature.

That might be what you encountered: the motor, unable to start, was making a horrible racket.

That can also damage the compressor motor. So don't do that again.

If the system is working ok now you may have been lucky and avoided serious damage; else you'll need a service call.

 

Loud banging noise 5-10 minutes prior to the heater turning on

Our heater is driving me insane. It makes a loud banging noise 5-10 minutes prior to the heater turning on. It’s only at night when it’s colder out it seems. It can’t be replicated by the 2 techs we have had out

I created a sound bite and unfortunately neither has heard this noise before. It seems to be coming from the back of the unit or really internally somewhere near the copper pipe and insulated pipe on the left side of our electric Trane unit.

The strange thing is the heat runs all day without making this sound. It’s only at night from midnight on.

I know that sounds crazy. I’ve added the recording of the sound. The couple of additional thunks are me trying to get the closet door open. Any recommendations would be much appreciated. On 2019-01-04 by Lindsay

On 2019-01-04 by (mod) - Loud banging noise at heater at night driving me crazy

Lindsay

Let me extend sympathy for your aggravation; my own heating boiler has been making me mad for about five years, and I am (or was)a trained heating service tech.

It would help me guess at your heater banging noise if I knew anything at all about your heater: fuel, type: hydronic (hot water boiler) or warm air (furnace), age, brand, model.

Our own oil fired boiler would blip on for about 10 seconds - then off - with a bit of a burp - not normal operation and not something anyone could explain. We cleaned, tuned, changed primary and flame sensor controls, checked aquastat sensor in the well, improved draft, to no avail.

Last week our boiler just quit hard - which made finding the trouble easier: a failing transformer (something I'd suspected but not proved).

I asked the heating company to send an experienced service tech as we have had three prior repair attempts.

The service technician opined that the primary controller and transformer were "wired the old way and not correctly" and that overheating was leading to a lockdown of the boiler.

Now as today's NY Times editorial (David Brooks on selfism) would suggest "Enough about me..."

I suspect that you are hearing a type of water hammer noise, perhaps one that includes temperature as a factor.

Sometimes we can confirm water hammer - at least its diagnosis - by slightly changing the water velocity in the piping system. If there are flow balancing valves on your heating zone(s) try closing one or another of them just slightly to see if that makes a difference.

Also, if you can bear it, read these two articles

BANGING HEATING PIPES RADIATORS

(Example: some zone valves can cause water hammer noises)

and

WATER HAMMER NOISE DIAGNOSE & CURE

By becoming familiar with how water hammer noises show up, what they sound like, and their common causes, you can at the very least rule out or in this hypothesis about your insane-driving heater.

Watch out: be SURE to have also ruled OUT any banging noise traced to the start or end of the operation of the burner - as that condition could be dangerous.

For oil fired heaters read more at OIL BURNER SOOT & PUFFBACKS

For gas fired heaters read more at GAS BURNER FLAME & NOISE DEFECTS

For other noises that may be traced to air handlers and ductwork that expands and contracts or perhaps a blower motor problem or for heat pumps, other problems, see see HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing, thumping where we catalog all sorts of noises by the sound type: such as bang, whir, scream, etc.

Keep me posted, and contact us to send your noise recording if you like, using the page top or bottom CONTACT link.

On 2019-10-26 by Chad loud repetitive bang, bang bang bang bang

So here is a question for someone, I have a AirEase heat pump a/c unit in my attic for the 2nd floor zone. It is 6 years old.

Now that the seasons are changing and it’s getting colder at night my heat kicks on during the night, once it reaches desired temp the outdoor fan unit will turn off the indoor unit in my attic has a 90 second delay for all of the air in the ducts to be blown out before it shuts down.

After this happens about a min or so later I get a loud repetitive bang, bang bang bang bang Which sounds like it’s coming from the line set and back pressure of some sort. Does anyone know the cause or the fix for this banging. It is loud enough to jolt you out of bed thinking someone is banging the door.

And this is only happening during the night not during the day so it makes me think the outdoor low temp is a problem?

On 2019-10-26 1 by (mod) - diagnosing your banging heat pump

Chad

let's start diagnosing your banging heat pump at

BANGING A/C or heat pump

and continue at

BANGING NOISE at AIR HANDLERS or in DUCT SYSTEMS

and after you've been through those diagnostic suggestions don't hesitate to post follow-up comments, observations, questions, and we'll continue from there.

On 2019-10-26 1 by Anonymous - more banging noise at AC unit

Ok so when my service tech was out to look at it the other day we went through all of his testing. We tried to make the unit make the noise but it didn’t happen when he was there. It was also 62 degrees outside during the day when he was here to service the unit.

This noise happens during the middle of the night when the outside temp drops below 40 degrees. Like I said before it does not make a noise during start up or during operation it makes the noise after it meets inside thermostat temp the unit shuts down air stops blowing and outside unit is off no fan moving.

And then the banging starts almost like the refrigerant in the line set or pressure in the line set is the noise. It’s odd. It’s a rapid bang. Bang bang bang bang for about 8-12 seconds which seems like forever in the middle of the night.

 

Loud banging noise at heater before turning on

Our heater is driving me insane. It makes a loud banging noise 5-10 minutes prior to the heater turning on. It’s only at night when it’s colder out it seems. It can’t be replicated by the 2 techs we have had out. I created a sound bite and unfortunately neither has heard this noise before. It seems to be coming from the back of the unit or really internally somewhere near the copper pipe and insulated pipe on the left side of our electric Trane unit.

The strange thing is the heat runs all day without making this sound. It’s only at night from midnight on. I know that sounds crazy. I’ve added the recording of the sound. The couple of additional thunks are me trying to get the closet door open. Any recommendations would be much appreciated. - On 2019-01-04 by Lindsay -

On 2019-01-04 by (mod) -

Lindsay

Let me extend sympathy for your aggravation; my own heating boiler has been making me mad for about five years, and I am (or was)a trained heating service tech. Our heater would blip on for about 10 seconds - then off - not normal operation and not something anyone could explain. We cleaned, tuned, changed controls, improved draft, to no avail.

Last week our boiler just quit hard - which made finding the trouble easier: a failing transformer (something I'd suspected but not proved).

Now as today's NY Times editorial (David Brooks on selfism) would suggest "Enough about me..."
(I meant the above to be entertaining and encouraging).

I suspect that you are hearing a type of water hammer noise, perhaps one that includes temperature as a factor.

Sometimes we can confirm water hammer - at least its diagnosis - by slightly changing the water velocity in the piping system. If there are flow balancing valves on your heating zone(s) try closing one or another of them just slightly to see if that makes a difference.

Also, if you can bear it, read these two articles

https://inspectapedia.com/heat/Banging_Pipes_Radiators.php BANGING HEATING PIPES RADIATORS

(Example: some zone valves can cause water hammer noises)

and

WATER HAMMER NOISE DIAGNOSE & CURE

By becoming familiar with how water hammer noises show up, what they sound like, and their common causes, you can at the very least rule out or in this hypothesis about your insane-driving heater.

PS be SURE to have also ruled OUT any banging noise traced to the start or end of the operation of the burner - as that condition could be dangerous.

Keep me posted, and contact us to send your noise recording if you like, using the page top or bottom CONTACT link.

Humming Noises at HVAC Equipment, FAQs

Condenser unit hums for 2 seconds before starting-up

Outside unit hums on start up about 2 seconds and then runs normal. - On 2018-03-11 by Pap

Reply by (mod) - Outside unit hums on start

Sounds like a hard-starting compressor.

You might extend the life of the system by installing a hard-start capacitor for the compressor motor.

Humming at rooftop evaporative cooler stops if I run water

Hi, I have an evaporative aircon. It's making a loud humming noise and when I turn on the kitchen tap the noise stops. Do you know what could be wrong? Thanks. Chris - On 2019-12-08 by Chris -

On 2019-12-08 by (mod) - water pipe noise

Perhaps there is a water pipe noise changed by changing pipe flow rate or a rooftop water pump that's loose or has a failing motor.

Condenser switch stops humming when tapped

There is a switch I think in the condenser and if I tap it it stops humming unnoticed wire was loose on it.

Every time I put it back on it hums and pops off . Is it the switch or is that a safety thing that does that to prevent more damage from another part. - On 2020-07-30 by Stephen borden -

Reply by (mod) - replace failing HVAC relay

You are describing a control relay that is failing and needs to be replaced.

2-minute humming sounds from our HVAC system at 1AM

Randomly, around 1AM there is a humming sound that starts out low and ends high (lasts about 1-2 minutes). It is not reproducible, the HVAC guy replaced the filter on the first trip, blower motor on the second but it continues. I recorded it this morning at 120AM, it sounded strongest around the whole house humidifier area.

@Jeff R, Also, turning the furnace off at the thermostat does not make the noise stop, nor switching form cold to heat.. On 2018-08-21 by Jeff R

Reply by (mod) - Diagnose the humming sounds by following the clue frrom your HVAC guy:

Jeff

Diagnose the humming sounds by following the clue frrom your HVAC guy:

Look at what electrical equipment might be running or trying to run.

A motor that is having trouble will often hum - before it burns-up or fails.

Search InspectApedia.com for ELECTRIC MOTOR DIAGNOSIS or for HARD START CAPACITOR to understand more about that possibility.

Of course replacing an air filter won't mean much to a failing blower motor, but maybe the tech figured as long as she'd gone to the trouble to look at the system she might as well do something useful.

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

On 2020-06-01 by Lorrie - Loud Hum near AC Units

Have lived in my small condo unit (~1000 sq ft) for 20 years. Last summer I started hearing a loud hum, loudest near the wall where the AC units in my stack lives- when my AC is not on.

I also feel and hear a vibration (imagine a sneaker in a dryer or a treadmill) most noticeable when you sit down to watch TV or read a book. It is often intermittent. The TV volume must be turned up to override the sound and vibration.

This morning the sneaker started at 4:15 am. I went to bed at 11:30 pm and the noise was present. So it is obviously coming from another part of the building.

I am on the 2nd of 4 floors with one neighbor to the right and one to the left. I have had 2 electricians check when the panel in my unit is turned off, a plumber to check the hot water heater, the guy upstairs says he hears nothing and the owner's electrician has said he hears nothing up there

. I need a troubleshooter and not someone who is going to tell me to live with it. I am 69 years old and do not have Wonder Woman hearing capacity. Please advise. I am in the Ft Lauderdale/Palm Beach part of South Florida.

On 2020-06-01 - by (mod) -

Lorrie

If there is humming and vibration when your particular AC unit is not on then most-likely it's a neighboring unit transmitting sound and vibration. I agree that "live with it" sounds a bit foolish for a number of reasons, including a pending complete failure of somebody's equipment.

If none of the neighbors cares now, I figure they will fix the problem when their unit fails solid.

Or you can see if a local home inspector or similar building diagnostician can help out. Some of these are in the page top EXPERTS DIRECTORY - discuss your needs and ask what the person will do before hiring someone.

At HVAC NOISE-3 HISS HOWL HUFF HUM https://inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions_3.php

we list common sources of this humming type noise problem.

Clicks, Clanks, Tapping Noises at HVAC Equipment - FAQs

Loud clicking/ clanking noise from the outside heatpump/condensor unit

Our system all the sudden started acting up. noticed only warm air coming out of the vents inside. checked thermostat and it had nothing on the display(like it was off).

I heard a loud clicking/ clanking noise from the outside heatpump/condensor unit. Went outside and the noise was coming from where the wiring went into the side of the unit. the fan was still running on the unit. I can smell some electrical burning smell. I shut off the system by hitting the circut breaker...help. loud clicking/ clanking noise from the outside heatpump/condensor unit On 2012-06-26 by Need Help

Reply by (mod) -

Watch out: MOST IMPORTANT: if you smell something burning, turn off the equipment immediately and leave it off. If there is further evidence of a fire or smoke, get people out of the building and call your fire department.

When your thermostat shows nothing on its display, start by checking to see that the indoor heating or cooling equipment has power - often you'll find that it has been switched off or has perhaps tripped a circuit breaker or blown a fuse.

If the equipment has power, next I check for loose or damaged thermostat wires or a bad thermostat transformer.

When you hear a loud clanking at the outside compressor/condenser unit the news sounds worse - often that is an indicator of a failing or failed compressor unit. You need a service call by an experienced HVAC technician.

See also our noise sources

at CLICKING NOISE DIAGNOSIS & CURE

Question: heat pump makes a metallic noise

The heat pump makes a metallic noise constantly, even if outside is 16 gr C. I am sure it is not ice. On the contrary, when the A/C is on, the metallic noise disappear. The heat pump is now 3 yrs and it was noisy from the beginning.Does anyone have any idea? Thank you so much! (Sept 28, 2015) Laura said:

Reply:

Laura, see RATTLING & vibration noises from A/C or Heat Pump System

Laura: Your service tech may want to check the reversing valve.

 

Question: tapping sound in wall where refrigrant piping runs

I have 10 year old heat pump where the interior unit is located in the attic, the exterior near the house, and the coolant pipe is run through the exterior wall of the house to connect the two units. Over the past couple of years there has been a "tapping" sound in the wall where the coolant pipe is located.

That tapping does not occur when the unit is running and stops about 5 minutes after I turn the unit off. I have checked the condensation pipe and it is not that. Any ideas? (Feb 14, 2016) Don said:

Reply:

Don:
Could we be hearing movement of the piping through a tight opening or across a surface due to thermal expansion / contraction as the refrigerant piping temperatures change?

 

Question: American Standard unit Clicking noise

My American Standard unit outside is clicking, it turns on, Clicks turns right back off or on. It does this for 2-4 times then it will run for a couple minutes. Then it repeats the cycle. I have it onow video any suggestions? (Aug 6, 2016) Kelly said:

Reply:

Kelly please see CLICKING SOUNDS from air conditioner or heat pump system, then see our discussion of chattering relay switches and controls

at RELAY CONTROL SWITCHES and let me know how that works for you and your service technician.

 

Question: loud blower unit, loud snapping and clicking noise

I am in a brand new build apartment with a Goodman air conditioning unit. The blower is extremely loud, and there is an extremely loud snapping and clicking that happens whenever the unit kicks in. The sounds are coming from just behind the filter in the main vent to the living room.

I have had the guy who installs the units look at it and told me it was the condenser coil making the noise and there is nothing he could do about it. Other apartments have also complained. The guy across the hall has to sleep with the bedroom door closed.

I have not gotten a single night's sleep since I moved in here due to this noise. What can I tell them needs to be done to correct the noise. If I had this installed at my house, I would have had it ripped out the next day. I haven't read anything yet that seems to be something that I can take to this guy that denies that the noise can be fixed. Thanks in advance for any help you folks can give! (Sept 5, 2016) Anonymous said:

Reply:

Anon there are two different concerns that occur to me:

1. The blower speed and sound and air velocity vs. duct design, insulation, requirements, and perhaps soundproofing between you and the AC unit

2. Loud clicking and snapping that you hear in, at or near the air handler or through nearby HVAC ducts, especially when the blower unit first starts are often traced to a very excited electrostatic air cleaner who is zapping dust particles loosened when the air flow starts up.

Clicking sound, directly above the air filter, AC struggling

The hot season is fast approaching so I am finally using the AC.

I have a nest thermostat and I turned the dial to 76 and it almost sounds like the ac is struggling to keep itself on

. I can hear the sound, directly above the air filter, it’s like a clicking sound. Any help? On 2019-04-24 by Chanda -

Reply by (mod)

Chanda

I'm uncertain what's wrong with your AC as there could be many causes of hesitated or hard-starting, ranging from a corroded or bad contactor or loose electrical connection to a hard-starting, failing compressor motor.

To avoid further damage or even a risk of electrical fire I would turn the system OFF at the electrical panel and call for repair.

Let me know what the service technician tells you as that may permit us to make further more-useful comments and as it will help other readers.

How do I fix a loud clanking noise from my A/C

I recoreded a video/sound of my unit

I have a clanking noise that I've noted is heard within a certain temperature range. I don't hear it when it is very cold, and I've never heard it when I use the AC. My heating and cooling has been working.

I heard a similar sound on a clip you had on BANGING A/C or heat pump - "Banging or Hard Starting Compressor Condenser Unit Video"

Any suggestions will be appreciated. I do not have the funds to replace this so I need to have an idea of what is going on and if it is repairable.

I also don't have the funds to have a number of visits wihout resolution, so if I can provide a tech with some ideas of what is going on that would help. The tech I had here a while back was not able to help, but of course it wasn't making that sound when he was here and I didn't have a recording at the time, so he was flying blind.

Thank you! My email is sarnaiz @ verizon.net - On 2016-12-14

Reply by (mod) -

Sarniaz,

While we have listed common causes of various HVAC noises and while we describe repairs for various HVAC problems at InspectApedia.com, I have found that people's interpretation of the name, source, and significance of sounds varies so widely that I'm never 100% confident in the remote email- or e-text diagnosis of a noise that we hear or have reported.

To minimize the cost to you of repeated visits - a legitimate concern - I suggest a thoughtful discussion with the service manager of the company who services your HVAC equipment.

Explain your situation and as that they send a senior, experienced HVAC service technician to give the best chance of an economical and proper repair.

There is almost no chance that a homeowner can repair problems with a compressor motor, control board, relay, or refrigerant that are common causes of the noise you describe.

Thumping Thundering Noises at HVAC Equipment, FAQs

Thunder rumbling from my air conditioner

Hi DanJoe, I still have the rumbling in my YORK 2-speed motor AC system. It has gotten worse, and louder.but I haven't called the technicians who installed it because, sadly, I don't have much confidence in the ones who have come out in the past and don't know how to find a really competent one from another company.

The rumbling, like thunder is coming from the inside air handler, and goes on for anywhere from 30 seconds to a minute before the fans kick in. There are 2 speeds and I've been trying to figure out if that is involved in the problem.

It's very nerve-wracking hearing this noise when the unit itself is sooo quiet; that being the reason I chose it. Do you think I'm risking permanent damage to something by stalling getting a repair person in here? Thanks to you and anyone out there who can help me! On 2014-08-13 by Ginger Vela

PS sometimes the rumbling goes on a bit after the one fan speed comes on.

Reply by (mod) - success with the quality-of-service problem by speaking politely with the service manager

Ginger,

I've had success with the quality-of-service problem by speaking politely with the service manager at the company you use.

Explain that the problem has been looked at with no satisfaction, that it's getting worse, and that perhaps it might even be unsafe - ask that an experienced senior tech be sent to your home. Let me know what ensues.

I suspect they're going to find a bad air handler motor or loose HVAC ductwork metal.

Followupby Ginger Vela

First of all, thank you for your response which I just read. This morning I called the company that installed my unit and a very familiar tech came out within an hour.

I set the system to kick on when he arrived, and he HEARD the noise! His diagnosis; a failing motor. This unit has an *ECM motor, and one is on order for me.

Luckily, it is still under warrantee, and I will only have to pay for the labor. I've had bad luck with the functioning of this model which needed a new compressor which started failing about ONE YEAR after its installation in 2009 and now this motor failure issue.

It's called York Quiet Drive model It cools great and is beyond belief as far and quiet and efficiency go, except for the nerve-wracking noises of failures of those two components. I am so relieved to know what's wrong and to be able to get it fixed.

Unfortunately, my cooling savings have been offset a bit by the installation/labor chg. for the new compressor of $767.50, +a new evaporator coil in 2012, and now whatever the labor is for this motor. I'm told it will be a lot less than the compressor install.

Thanks so much for your help and encouragement. Just so you know, there is no service mgr., and the owner/ salesperson made himself scarce once the initial job was done, only once agreeing to speak with me on the phone at my insistence. Sincerely, Ginger

I will ask him. Thank you. I wondered about that as we do have fluctuations sometimes. The power Co., Florida Power and Light, is always trying to sell surge protection. I also have a SMART METER, (against my will) and did suspect it in the lose of the compressor.

I HAD it switched out for an old-style meter, and this motor problem started BEFORE FPL pretty much forced us have the SMART METERS reinstalled this May or else PAY a surcharge each month.

Will definitely ASK. Also, I have a very old house which does need an electrical upgrade. 1936 house.

Don't like the thought of it being all torn up for that work! Will keep you posted. Thanks GV

Followup by GV

DanJoe, The technician came out again, and I now have a new air handler blower motor.

System is working well and so much quieter. He did not think fluctuation in power was a likely cause since there are safeguards against it in the unit. Thanks, Ginger

Reply by (mod) - York Quiet Drive

Thanks for the follow-up GV - it will help others.

YOu might ask the installer to check for any conditions that might contribute to early motor failure such as voltage variations.

 

Loud Thumping sound from LG A/C Unit

When my L.G 1.5 ton strip A,C. whenever it is switched off after half an hour running, makes a loud thumping sound. What is the likely reason for this heavy thumping sound Please? Can u tell me?

On 2013-03-10 by Valerian

Reply by (mod) -

Valerian,

Thumping A/C equipment doesn't sound good. But first we need to know what's thumping; could be components that are loose, or something else.

Start by seeing if you can trace the noise - to the indoor or outdoor components to start.

 

Thumping Noise from Air Conditioner

I'm at my wits end over this.... I moved into a 20 year old condo two years ago.

I'm on the third floor of a four story building. Intermittently, I hear a clanking noise that sounds like someone throwing a tennis ball against a cement wall.

I hear the noise throughout my entire apartment because the noise is coming out of my A/C vents. I even hear the noise if all my power is turned off. On 2017-05-15 by Ralph S

Reply by (mod) re: clanks, clunks, noises like tennis ball tossed against a wall

Ralph:
You've done one of the good steps in tracking down the source of an annoying noise by turning things off. Here are some more considerations:

A neighbor's mechanical system or equipment could be running, so more turn-off diagnosis could help

Metal ductwork often makes noises like those you describe as the ducts expand or cool: sheet metal clunks and thumps. Those sounds are usually most noticeable near the start or after the end of an HVAC system turning on or off or its blower fan turning on or off.

If you have not done so be sure to read

CLANKS CLUNKS from air conditioner or heat pump system - found at inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions_2.php#Clank

Track down the noise to its source by careful listening, with helpers, in various locations to see where sound is loudest.

Try using our NOISE LOG (search InspectApedia using the search box above) to relate noises to weather, temperature, time of day, etc.

Low to fast “drum beat” or a sound like filling up your car windshield washer reservoir

After AC unit shuts off we eventually hear a slow to fast “drum beat” or a sound like filling up your car windshield washer reservoir - On 2019-06-25 by Tom -

On 2019-06-26 by (mod)

Perhaps there is a refrigerant leak, low refrigerant in your system, and air bubbles in the piping. Could that be what you are hearing?

Upon start up, the a/c makes a rip cord like sound.

Here's a flabergaster. We have had 5 techs now to look at our A/C unit and no one has ever heard a unit make this noise in all the 20 or 30 years they have been a tech. This all started 2 weeks ago when we had a solar panel installed on our water heater and the NEST thermostat on our unit.

Upon start up, the a/c makes a rip cord like sound. Like a rigid piece of plastic is being pulled through a tight spot, or - well - someone cutting a very bad, gassy fart.

It ONLY does this after the system has completed its OWN cycle and at start up. We have had a blower wheel and motor replaced.

Found a piece of cardboard stuck in the system and the tech will be coming out tomorrow to inspect it again.

Someone suggested it might be our HEPPA filter, but we took it out for 2 cycles and it still made this horrible noise.

I think whatever damage has been done to our system is now not only affecting the handler but is now affecting the unit outside. Any help and suggestions are welcome. On 2012-09-13 by Teresa -

Reply by (mod) -

Teresa

Use the contact us link at page top or bottom to send us a reording of that odd noise - it may permit further comment.

...

...

Continue reading at NOISES, HVAC SYSTEM DIAGNOSIS - home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see HVAC SYSTEM NOISE DIAGNOSIS FAQs-2 - more-recent questions and answers about noise in heating, air conditioning, or venting systems

Or see these

Recommended Articles

• HVAC SYSTEM NOISE DIAGNOSIS - home
  • AIR HANDLER / BLOWER NOISES
  • CHATTERING RELAYS, HVAC EQUIPMENT
  • COMPRESSOR CONDENSER NOISES
  • DUCT SYSTEM NOISES
  • DUCT VIBRATION DAMPENERS
  • ELECTRIC MOTOR NOISE DIAGNOSIS
  • FAN NOISES, HVAC
  • HVAC SOUND DESCRIPTIONS
  • HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing
  • HVAC NOISE-2 CHATTER CHIRP CLANK CLICK FAN GRIND GROAN - chattering, clanks, clicks, clunks, cyclical, fan, groans, growls, honking
  • HVAC NOISE-3 HISS HOWL HUFF HUM - hiss, howl, huff, hum, groan, woo wuu wuff
  • HVAC NOISE-4 POP, RATTLE, ROAR, RUMBLE - loud start, pop, rattle, rumble, water, silence
  • HVAC NOISE-5 SCREAM SING TRUMPET WHINE WUWU - scream, sing, squeal, trumpet, wawa, wowo, water gurge, whine, whistle, wuwu
  • NOISES, HVAC SOUND RECORDINGS
  • REFRIGERANT PIPING GURGLING

Or see this

List of Common HVAC Failures that Cause Noises

• BURNED-OUT COMPRESSOR
• CAPACITORS for HARD STARTING MOTORS
• CONTACTOR RELAY DIAGNOSIS & REPAIR
• CONTROL CIRCUIT BOARD, A/C
• COPELAND ELECTRICAL HANDBOOK [PDF]
• CRANKCASE HEATERS
• FAN, COMPRESSOR / CONDENSER UNIT
• FAN NOISES HVAC
• HARD STARTING COMPRESSOR MOTORS

Suggested citation for this web page

HVAC SYSTEM NOISE DIAGNOSIS FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING NOISE DIAGNOSIS

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