FAQs about how to diagnose these noises: clanks, clunks, cyclical, fan, groans, growls sounds at an air conditioner or heat pump.

This air conditioning repair article series discusses the diagnosis and repair of air conditioning compressor noises which range in importance from normal (if annoying squeaks and squeals, to rattling loose bolts and hardware, to costly compressor damage indicating air conditioning compressor or A/C compressors at or near end of their life.

HVAC Noise Group 2 FAQs

These questions and answers about diagnosing chattering, clanking, or fan noises such as clank, clunk, groaning, or gurgling noises at an air conditioner or heat pump system were posted originally

at HVAC NOISE-2 CHATTER CLANK FAN GROAN - chatter, clank, clunk, cyclical sounds, fan noise, groan, growl, gurgle noises, - be sure to see the suggestions at that page.

On 2019-10-11 by (mod) - when we hear bubbles in the refrigerant lines it's usually a sign of low refrigerant charge

Normally when we hear gas bubbles in the refrigerant lines it's a sign of low refrigerant charge which means a leak

On 2019-10-11 by Anonymous

I never thought that a transformer would make this noise. I'm not sure I can replace just the transformer on this model unfortunately.

On 2019-10-0 by Ian

you know I thought that at first but it happens throughout the entire cycle. I’d figure that eventually the coil would eventually equalize after some time. I was next wondering if it was the sound of liquid refrigerant boiling into gas.

The coil is very clean.

you know I thought that at first but it happens throughout the entire cycle. I’d figure that eventually the coil would eventually equalize after some time. I was next wondering if it was the sound of liquid refrigerant boiling into gas.

The coil is very clean.

On 2019-10-04 by (mod) -

Ian

Is this perhaps thermal expansion or contraction?

Has anyone tried cleaning the coil?

On 2019-10-04 by Ian

I have a thru-wall unit. The evaporator coil can sometimes emit an intermittent crackling sound, not unlike the sound made when crumpling cellophane. Its totally random in its repetition. It goes away, and then comes back. It is then always audible as soon as the compressor cycles off, for a few seconds, and then goes away.

I used to think it was the styrofoam scroll housing for the blower fan adjusting to the changing temperature and humidity when the compressor cycles on but I don’t think that is it.

On 2019-04-06 by (mod) -

I'd look for a failing transformer

On 2019-04-04 by Kai

So, we've decided to go smart. And for the most part it's great! Except, I've noticed since installing the new thermostat there's an intermittent light humming sounds after the a/c kicks on to cool down. We've also noticed that if we turn the thermostat back to the previous number and back to the lower temperature the humming noise stops.

On 2019-02-21 by (mod) -

Thank you for the feedback Pete it will be helpful to other readers as well. Do keep us posted.

On 2019-02-21 by pete - replaced bad circuit breaker

After replacing the breaker, everything has been working well. Thanks for your help! I'll be back when there's time to troubleshoot the rumbling in the furnace fan. Your site is awesome.

I replaced the condenser fan today and it's running smoothly and quiet. No TICKING NOISES! Now we'll see if the furnace blower is also bad. Things happen in "twos" a lot (at least for me). I'm going to replace the furnace circuit breaker also because it looks slightly different than all the other breakers, as if it's been replaced in the past. Thanks for your help, I'll let you know if everything is okay.

On 2019-02-04 by (mod) -

Sometimes damaged electrical wire insulation can be very difficult to spot with the naked eye

. It would be so expensive to do so I would be inclined to replace on a suspect wires particularly ones that are near or touching electrical components. There's also arcing that can occur inside of a relay or even on a circuit board.

On 2018-05-17 by (mod) - turn off Humming motors that are not running

If the humming noise coming from an electric motor is new, it's almost certainly not normal.

I would turn OFF the system and call for repair. The problem could be a failing motor or a bad motor start/run capacitor, or, of course, something else.

Turning off a huming motor that's not running can help avoid a fire or other damage.

On 2018-05-17 by Ellen

My system starting humming real loud woke us from our sleep is this normal

On 2017-07-14 by Shmuel - Intermatic HB112

I should add that the Intermatic HB112 you recommended may be problematic due to the outlet being on the side of the timer. Since the plug of the AC is pretty wide, I am not sure there would be enough clearance from the wall to insert the timer into the outlet with the AC plug inserted. What are your thoughts?

I actually had thought about this *automatic re-start feature* you mention as a workaround for the Sabbath, but I understood this to refer to the settings memory rather than the unit actually turning itself back on. It appears though from the link you provided that it actually powers the unit back on. Thank you so much for this. God willing I will get back to you after trying this out with the timer you recommend.

On 2017-07-13 by (mod) - specifications for the LG LW1216ER

Thanks for the follow-up Shmuel, that will assist other readers deciding about fixing vs replacing old equipment that needs costly repairs.

About timers: the LG LW1216ER is a window air conditioner. The timer limitation you describe is built into the A/C controller itself. But there is another option, installing a timer on the electric circuit or receptacle into which the air conditioner is plugged.

The specifications for the LG LW1216ER at www.lg.com/us/support/products/documents/LW1216ER%20Spec%20Sheet.pdf note that the unit consumes 990 watts and draws 9.3 Amps.

According to LG your unit has an automatic re-start feature that turns the unit back on after a "power failure" -

so perhaps you could just leave the A/C controls "on", then use a separate timer like the Titan Controls 734112 - Apollo 7, capable of handling 15 A / 1725 Watts, or the Intermatic HB112 Mechanical Timer - heavy duty and rated for 3600 watts, should do what you need.

As it doesn't do what you want, leave the LG air conditioner's built-in 24-hour timer off entirely, set the air conditioner to ON, and let your receptacle timer turn the unit on and off (a pseudo "power failure") as you wish. Just be sure to get the settings done before sundown Friday. Shalom.

On 2017-07-13 by Shmuel - want a timer for a window air conditioner

Thank you danjoefriedman for your response. I ended up throwing out the AC & replacing it with an LG LW1216ER 12,000 BTU unit. A shame since when the old one worked it really cooled the room quite nicely. I should add that the new unit works well.

The issue I have with my new unit is that the controls are digital and the timer is only a delay on or delay off.

Thus I can no longer use a timer connected to the plug which allowed me to set the AC to turn on and off multiple times.

My old unit was a manual turn on/off so I was able to leave the dial in the on position and let my timer control when it goes on and off.

For me being a Sabbath observer and not turning on and off electrical appliances on the Sabbath, the manual on/off switch was fantastic since I could have the timer turn off the AC at night and then have it turn back on in the morning. With the digital on/off I only have the option of either having it turn off but not on, or turn on but not off. (via the unit built in timer)

On 2017-07-07 by (mod) -

Derek, my best guesses are at

GROWLING compressor sounds

On 2017-07-06 by derek

my keeprite 1.5 ton unit makes a growling noise for a couple of seconds as it shuts off during the cycle. Any thoughts

On 2017-07-05 by (mod) -

Sounds as if there may be a coil icing problem. Your service tech may find a refrigerant leak.

On 2017-07-04 by Eric K

I went to change the filter and noticed it was wet. There was a drip coming from within my furnace. I turned of my a/c and after a few hours the drip stopped. I turned the a/c back on and the dripping started again. Now, on top of the drip, when the a/c turns of there is a noise coming from the pipe leading from the furnace to the roof.

It sounds like pieces of something falling down the pipe. Some sound metallic like screws, some soundike pieces of non matallic things falling. This only seems to happen for the first hour after the a/c turns off.

This can't be good!

On 2017-06-18 by Shmuel

I have a Quasar window AC. It is pretty old but it still blows cold air. The problem is after working for around 2 hours it starts making groaning noises & while the air coming out still feels cold, it is no longer actually blowing the air well.

You literally have to put your hand up to the air conditioner & then you barely feel any air coming out. On first thought it sounds like a bad fan. But I wonder because for the first two hours or so of operation the unit blows out cold air just fine. (and there is no groaning noise) I need to let it rest for about an hour or two & then if I turn on the unit it works fine again. But then the cycle of going bad after two hours of operation starts all over again. What are my best options?

On 2017-06-06 21:49:01.590185 by (mod) -

Darn, how annoying. I can but suspect that air movement over something loose or exposed in the air handler or duct or air movement through a restriction is causing the trouble.

If inspection doesn't show something obvious, I would do some experiments to see if we can change the airflow pattern into or out of the air handler. Perhaps even something as simple as placing a brick in the ductwork above the unit?

let me know how that works for you.

On 2017-06-06 by Rachel

New HVAC went in today. Installed into hall closet required trimming of plenum to fit new unit. When air conditioner on sounds like a low pitched continuous horn sound. Why? Thanks

On 2017-05-31 by hf995

I have a brand 2 new Friedrich window AC unit. If the compressor is run for over 15min and then is shut down by switching to "fan" mode, the unit makes a rattling/clicking sound in the lower of the 2 of 4 fan speeds. After about 30min of "fan only" operation the noise will dissipate and go away for the most part.

If the unit has been off for an extended period and is started up directly into "fan only" there will be no noise. Is this just a normal post compressor operation sound or something to be concerned about? Thanks!

On 2017-05-22 by (mod) -

I suppose there could also be a bad control board or relay that's turning the fan on and off when it shouldn't - you'd detect that with a VOM on the fan power leads - watch out for shock hazards and fingers that get chopped off

On 2017-05-22 by (mod) -

Jay, good going - so far.

With power OFF I would try wiggling gently the fan blades to be sure that the blade is securely fastened to the new fan motor shaft and that the motor shaft itself is not loose in its bearing.

Then spin the fan slowly and watch to see if a blade is bent out of the plane with the rest of the fan

On 2017-05-22 by Jay Thomas

I replaced my condenser fan motor and dual capacitor. AC is working well and condenser fan turning well.

But it doesn't sound smooth. It doesn't look like there is hesitation since it is running so fast but it sounds like there is. Instead of a smooth whooooooo sound, it is more like whooo, whoo, whooo, whooo. Could it be the blade?

On 2017-05-15 by (mod) -

I'm not sure what's happening in your system, Dee, and an onsite service tech will certainly be smarter.

But I'd start by looking at the common causes of reduced air flow, like
- a dirty air filter
- ice or frost blocking the cooling coil

On 2017-05-15 by Dee

Our a/c unit is a split system unit. Our a/c runs but the doesn't hardly blow through the vents, nor does it feel as cold as it use to. It isn't bringing the temperature down in our home. Whenever the unit shuts off, we hear a crackling noise that lasts for anywhere from 1-3 minutes after it shuts off.

Any idea on what this could possibly be?

On 2017-04-05 by (mod) -

Sounds like a sticking or failing relay, but I'd check first for a loose or wobbly fan blade.

On 2017-04-05 by Adrian

Heat Pump Condensor Fan makes loud chattering noise at startup and clunk noise at shutdown. But not at every cycle. What is possible problem with motor?

On 2016-07-24 by (mod) -

I'd start by watching the supply plenum and ductwork near the air handler at the start of a cooling cycle: often temperature or air flow changes can cause a sudden buckling or expansion or contraction in metal components.

On 2016-07-24 by Yvonne

A few seconds after my air comes on I hear a thud/crack sound coming from the attic where the air handler is located. It lasts half a second, but I hear the sound in a different area in the house each time the sound is made, which seems odd.

On 2016-07-13 by (mod) -

I can't tell if you're saying that after thudding the system no longer works - or it thuds but works. If the latter, you may be in time to avoid more costly damage by asking for a service call to find and fix the loose or failing component.

On 2016-07-13 by Lisa

My A/C cools fine and up until last night was not making any extra noise. Last night, a few seconds after the A/C started, I heard a single thud. I thought maybe my dogs were playing and ran into the wall or something. When I got up the next morning, I noticed it again.

It has been 3 hours since I got up and everytime it comes on, there is one noticable thud always a few seconds after it starts. There are no other unusual noises. The unit is 2 years old and the inside motor is 3 months old ( the original motor was faulty).

On 2016-03-31 by (mod) -

Marsha,

Since vibration noise can mean a failing bearing or motor, it may be that repair will be inevitable.

Let's hope that nothing more dangerous ensues: without an inspection to know just what is causing the noise I can't rule out a motor failure that could lead to an overheating condition or even a fire.

YOu need an onsite expert.

On 2016-03-31 by Marsha

I have a serious question that I hope business management will handle. In office where the hvac system is really loud. Periodically during the day there is a very loud vibrating noise that sounds like a helicopter and if I am in meetings everyone has to stop talking as we can't be heard when the sound occurs. The walls vibrate, ceiling tiles move and it sounds like something may come through the ceiling. The chief engineer for the building is to be contacted to discuss or examine. I have been told by other colleagues that have been in this area longer they were told nothing could be done about the noise.

However, it is not as loud there as in my office. Incidentntially the "normal"aor conditioning sound is also loud. I suspect the decibels are above what is considered normal. Can you suggest what this might be as I dont believe that there isnt anything that can be done as the organization was earlier told.

On 2016-02-29 by (mod) - Lennox heat pump roaring noise

Jimmie:

This indeed sounds puzzling, especially as you say you replaced key parts.

But what was not replaced were the controls that might explain fan behaviour. Some fans are variable speed and are controlled by either switches at the thermostat or at the air handler, or by a control board in the unit. I'd look for a bad controller.

On 2016-02-28 by Jimmie Durham

I have a Lennox heat pump & the fan in the air handler unit starts & runs fine for a few minutes 7 then roars and slows down & them stops & them starts & roars & stops again.

I installed a new air handler motor & capacitor & ounce in a while it did the same thing & then it run fine for a few months & started doing the same thing again. I've checked the wiring for loose connections. Any help?

On 2016-01-16 by (mod) -

Not dure. I'd check for a loose motor mount or a malfunctioning TEV or excess refrigerant charge.

On 2016-01-15 by Sara

When my outside unit turns off it makes a LOUD "CLUNK" noise and stops immediately as if someone shoved a stick in it. Any idea what this may be? Thanks

On 2015-10-19 by Anonymous

loud

On 2015-10-19 by michelle

heat pump and motor working BUT the fan that that goes on shaft seems like its missing something and making load noise when spinning or on and shavings are even coming off blades???? what is that

On 2015-09-29 by Jenny Gleeson

After it has been operating for an hour or so, my heatpump makes a sound like a vessel being filled up with liquid or gas, lasting about 25 seconds every few minutes when it is an active heating phase. It has done this since first installed a year ago. Any thoughts?

...

Continue reading at HVAC NOISE-2 CHATTER CLANK FAN GROAN - chatter, clank, clunk, cyclical sounds, fan noise, groan, growl, gurgle noises - toopic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see HVAC NOISE-2 CHATTER CLANK FAN GROAN FAQs-2 - more recent Q&A about these chatter, clank, clunk, cyclical sounds, fan noise, groan, growl, gurgle noises

Or see these

HVAC Noise Diagnosis Articles

• NOISES, HVAC SYSTEM DIAGNOSIS - home
• NOISES, HVAC SOUND DESCRIPTIONS
• HVAC NOISE-1 BANG BUZZ VIBRATE - ban
• HVAC NOISE-2 CHATTER CLANK FAN GROAN - chattering, clanks, clunks, cyclical, fan, fog horn moans and groans, growls
• HVAC NOISE-3 HISS HOWL HUFF HUM - hiss, howl, huff, hum, groan, woo wuu wuff or humming noises
• HVAC NOISE-4 POP, RATTLE, ROAR, RUMBLE - loud start, popping, rattling, roaring, rumbling, running water
• HVAC NOISE-5 SCREAM SING TRUMPET WHINE WUWU - scream, sing, squeal, trumpet, water sounds, whine, whoosh, whistle, wuwuwu, or silence

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING NOISE DIAGNOSIS

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