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Photograph of This new compressor was placed directly against a brick wall. One third of its condenser coil cooling ability was blocked. HVAC Noise Diagnosis FAQs-2

More Q&A on finding air conditioner or heating system noise sources

Air conditioner or heat pump noise diagnosis & cure questions & answers set #2:

MORE FAQs about air conditioner, heat pump, or other refrigeration system noise help track down the noise source and thus tell us how to fix it.

This air conditioning repair article series discusses the diagnosis and repair of air conditioning compressor noises.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

A/C & Heat Pump System Noise Diagnosis & Repair Noise FAQs Set#2

These questions on finding and curing noises traced to heating, ventilation, or air conditioning systems were posted originally

at NOISES, HVAC SOUND DESCRIPTIONS

Question: problems adding refrigerant in a research lab - liquid flood-back risks

(Apr 21, 2014) PP said:

I work in a research lab and we're using a split system to do some tests. We recently moved out of our lab space and so we had to remove all the refrigerant charge from the system and then charge the system again in the new space.

I've charged this unit before (just trimmed the charge 10% to 40%), but I've never had to charge the system from scratch. I've been having some problems with this-

I've added around 70% of the refrigerant charge to the system but I still don't see an increase in the subcooling. The subcooling is -68 C (:-/), the pressures are way way below the normal pressures, the EEV is wide open and there's no bubbling in the sight glass.

The compressor recently started having start up problems. It starts and then stops (Scroll compressor).

Am I looking at liquid floodback in the compressor?
How long do I need to run the unit before I see an increase in the pressure? There's been no increase in the pressure since I first started charging.

Reply:

PP:

If you are in any doubt about liquid flood-back, stop the system immediately. The result of liquid entering the compressor can be its destruction.

Normally we see the system pressures changing immediately as the compressor begins to run, reaching a stable HIGH and LOW side pressure after an interval that may be quite a bit longer: 10 minutes to 20 minutes in my experience, depending on the system size, cooling area addressed, heat losses and gains, ambient temperatures.

On commercial refrigeration systems I sometimes left a cooler running overnight to stabilize before checking again the next day.

That arm waving complete, if the system does not include a refrigerant receiver in its design it needs a precisely accurate refrigerant charge to work properly. Even with a refrigerant you need to be close.

The actual refrigerant quantity you need depends on not just the equipment as purchased from the manufacturer, but also the lengths and diameters of the refrigerant piping installed too - as that volume has to go into the calculation.

You'll need to get the charge right by adding the required volumes and charges together, starting with the manufacturer's spec. You may know that a refrigerant charge procedure also has to consider the temperatures at the time of charge.

Question: sounds like a sump pump

(July 18, 2014) Marie said:

I have a new 3T 14 SEER gas/electric package unit installed on the roof. When I started the AC for the first time, it doesn't sound like any AC I've ever had before. It sounds like a sump pump and initially blows hot air before the cooler air comes out of the vents. Is this normal?

(July 24, 2014) Adrienne Keen said:

Hi my air conditioner motor ( outside ) is leaking an enormous amount of water when it is first switched of What can be the cause of this Please Help Thank you

Reply:

Sounds as if the AC condensate is not being routed to a drain and properly drained away.

See

inspectapedia.com/aircond/AC_Condensate_Hazards_Leaks.php

for diagnostic help

Question: compressor is not starting properly

8/10/14 PKG said:

Hi , The compressor on my 3 Ton Amana A/C unit starts after 5 minutes of fan start ( there is no delay relay ) .. cold air blows out from top of the unit ..
and looks like compressor tries to start couple of times and finally starts on 3-4 try and then it works normal ..

Any advice will be appreciated.

Reply:

PKG

Sounds like a hard-starting compressor, possibly a failing compressor motor, possibly aided for a time by a hard-start capacitor kit.

Question: put the A/C compressor under ground to suppress HVAC noise?

(June 17, 2015) Andy Gough said:
Would an in ground compressor installation be an effective way to suppress noise?

Reply:

Perhaps it would, Andy, but on the other hand the cost of an underground HVAC compressor installation would be quite high as would be service and maintenance of such an installation.

As the compressor-condenser requires air movement across the condensing coil to operate the design would also still have to have openings to the atmosphere. In all I'm doubtful that such an approach is feasible.


On 2017-12-04 by Ava

The AC voltage box in the attic is making a loud humming or buzzing always. What could cause that?

On 2017-12-04 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 a bad connection, failing electrical component, and overheating or corroded or arcing connection, failing circuit breaker, Etc.

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.

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.




On 2017-07-02 by Manoj

Every 24 hours (6 am) a jackhammer type of noise comes out of only one duct (more than 10) in house, lasts for 60-90 seconds and stops. No a/c , or heat running. No noise at a/c unit. I am puzzled

On 2017-07-06 by (mod) -

Manish

I would start by finding just what. Equipment is starting up at that tim


On 2017-06-06 by GC Loud noise when clothes ddryer runs

l have a 2005 built 3 story condo. Recently whenever the dryer (on the 2nd floor) turned on, making a loud noise and vibration in the next room's ceiling even few minutes after dryer stopped. we can hear a loud humming noise and rattling bewteen 2nd floor and 3rd.

Repairman confirms there is no any issue from the dryer and no noise from dryer but when dryer operate. Can someone tell me what's the issue might be and who l should hire to fix the issue? Thanks.

On 2017-06-06 by (mod) - If the noise occurs only when the clothes dryer is running,

CG

If the noise occurs only when the clothes dryer is running, I'm hard pressed to buy a claim that the dryer has nothing to do with the sound. Perhaps it's a vibrating duct or vent hood for the dryer vent system?

You had a repair person on site. Did she not hear the sound, did it not occur, was it ignored? I'm confused.

On 2017-06-07 by (mod) -

Anon:

At this point it sounds as if we need a handyman(woman) or repair person to look into the ceiling where you hear the noise. You could try our page top EXPERTS DIRECTORY to see if you can find a home inspector with a borescope who will do a least-invasive look and diagnosis for you. OR you could see if the noise occurs only when the bath fan is ON - which would of course be diagnostic.

Another possibility might be a shared exhaust duct with the bath exhaust and drier exhaust (improper, illegal, unsafe) or a shared space in which two ducts run, one causing vibration in the other.

On 2017-06-07 by CG

Thank you for your suggestion. l hired the repair man. He came and operated the dryer and the dryer itself ran normally and very quietly but the loud noise plus vibrating starting occurred in the bathroom ceiling where is one room away from the dryer (not next to the dryer).

After stopping the dryer, the noise continued for over 5 minutes. The repair guy is specializing in Maytag dryer repair. He spent around 20 minutes checking everything regarding dryer motor, dryer vent, and anything might be related to dryer issue but nothing is found. At the end, he didn't even charge me the $90 originally need to pay for his visit.

Since he is not the HVAC nor house venting exhaust motor expert so he suggested the problem might be from the house exhaust fan/motor base on the noise came from between 2nd and 3rd-floor ceiling. l need your help to identify who l should hire? An electrician? Handyman? or? Thank you very much!

 

 


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


On 2016-12-14 by Sarniaz Fix loud clanking noise from my AC

Re-Posting

This is 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 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.

 

On 2016-09-21 by Joe Greaney

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 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.

Question: put the A/C compressor under ground to suppress HVAC noise?

(June 17, 2015) Andy Gough said:
Would an in ground compressor installation be an effective way to suppress noise?

Reply:

Perhaps it would, Andy, but on the other hand the cost of an underground HVAC compressor installation would be quite high as would be service and maintenance of such an installation.

As the compressor-condenser requires air movement across the condensing coil to operate the design would also still have to have openings to the atmosphere. In all I'm doubtful that such an approach is feasible.


Question: diagnose intermittent noises from an A/C unit

(Aug 26, 2015) Susan said:
I live in a townhouse with 8 units side by side. There is an intermittent noise which I am sure is my neighbors roof unit, because I have turned off my unit, and the neighbor on the other side has tested hers.

When I had mine checked for noise by the AC company, the repairman said it was working fine (great) and that the noise is normal (really?)
My neighbors with the noisy unit said they would have it serviced. The noise is loudest when I'm in bed on the 2nd floor, and almost goes away when I stand up.

Is there a way to insulate these roof units? Or my ceiling and walls? There is no attic, ductwork is between 1st and 2nd floor.
Thanks for all the information you provide.

Reply:

Susan:

First we need a diagnosis of the noise. For example if a motor or fan bearing is failing or there are loose components on the AC unit, repair is required and is straightforward.

Other "intermittent" A/C noises may be a motor trying to start, unsuccessfully.

If the HVAC tech says the particular system you describe are operating normally then discuss sound isolation with the HVAC service tech. For example, besides fixing mechanical problems, there are sound isolating pads that can go beneath rooftop equipment - though lifting it to add pads can be an expense.

Also see the noise and sound isolation article series beginning

at SOUND CONTROL in BUILDINGS -inspectapedia.com/BestPractices/Sound_Control_in_Buildings.php

 

Question: heat pump buzzing due to motor mounts?

(Nov 29, 2015) Margaret said:
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.

Reply:

Yes loose mounts can be a source of buzzing.


Question: copper line "exploded" on my heat pump

(Jan 1, 2016) Rich said:
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?

Reply:

Rich:

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).

 

Question: AC makes noise when switching on and off automatically - like a table saw

(Jan 11, 2016) Bree said:
One of my air conditioning units (the downstairs unit) has begun making a very strange noise (at least I think so) recently. It doesn't make the noise when I switch the unit on and off manually, but rather when it's running and automatically stops and starts.

When it stops, it makes a sound that I can only describe as sounding like a table saw. I had a technician out today, and he said that it's just the A/C unit switching over to defrost. I'm concerned because of the fact that I don't hear any other units in my immediate vicinity make the same noise.

It also makes a strange noise when it starts back up again. Does anybody know what that noise could be?

Reply:

Check the buzzing sound descriptions; I suspect a failing relay.

 

Question: heating units make popping noise at startup

(Jan 25, 2016) Michelle said:
For the past three weeks my heating units make popping noises (inside the attic) when it first comes on and for like 5-10 minutes afterwards. The first week, I heard a louder sound outside at start up (that stopped). The noise is annoying and interrupts my sleep.

I keep the thermostat on 68 (more so for the pipes) we're in the 30s or below freezing. Before I call out an technician, I would like to have an idea of what my problem maybe. I read the "ductwork noise" section, but still confused. Please help.

Reply:

See HVAC NOISE-4 POP, RATTLE, ROAR, RUMBLE - loud start, popping, rattling, roaring, rumbling, running water

 

Question: Lennox 3 & 4 ton XC16 with SL280UHV, SACH80V blowing warm air, straining noise at startup

(Apr 9, 2016) Ron said:
I live in the desert area community in southern CA and have a 5 yr old Lennox 3 & 4 ton XC16 with SL280UHV, SACH80V & ADP Coils on each. Last March the 4 ton unit started to blow warm air. The tech said refrg was low and added 4 lbs and system worked good after that.

March of this year same 4 ton unit felt liked it was blowing cool air but couldn't keep the temp we set inside the house.

Now I'm told there may be a slow leak in the line but they cant find any using bubble spray or by electronic sniffer. tech said the lines were frozen causing a loud straining noise at the condenser so I needed a kick starter since the system was too much amps a start up!

Qusetions are

1) if the lines are frozen and have very low refrig how can you find the leak?

2)shouldn't the refrig be topped off and then tested for noisey start up etc and leakage before now suggesting a Isolation test on lines? thanks

Reply:

The leak should be found and fixed; but I worry too that the compressor motor may be failing.

Adding 4 lbs of refrigerant is no "small leak" it's a catastrophe: dumping harmful refrigerant into the environment, dumping your money on the ground. I know that it can be hard to find and fix a leak (having made a market for "stop leak" additives that are somewhat controversial), but geez: converting the HVACR repair business into a delivery route for refrigerants is not so great a business plan and not too great for customers.

That griping said,

- icing can be caused by low refrigerant, until the refrigerant gets so low that there is no cooling at all

- yes icing up a thermostatic expansion valve can cause trouble for the compressor

A compressor can have trouble starting up against high head pressure that can occur if the TEV is not passing refrigerant out into the low pressure side of the system.

Leaks are found by inspection and testing.

Don't keep topping off refrigeant.

The extent of compressor damage can also be assessed by looking at its current draw.

 

Question: inside unit vibrating noise

(May 3, 2016) Aj said:

Inside unite was making a vibrating noise. Condensation around the base of the unit. Found the line and outside unit frozen.

Took out filter, turned on fan and let it thaw. I turned on the unit to AC this morning. It is still making the vibration noise but pushes cold air. Ideas?

Reply:

Start by looking close for loose motor mounts, door, or other mechanical components. Also have your HVAC tech check for a bad TEV.

 

Question: Air buffeting noise problems in HVAC systems: Cause & Cure

(May 27, 2016) Steve said:
Installed replacement air handler in Nov. Was fine until late spring when I began installing factory supplied a/c components. Upon installing coil shelf kit, there was unacceptable "air buffeting" @ air handler, even w/o the coil in place

.Needed a/c ,so set coil, had it hooked up.Cools fine, but have unacceptable buffeting. Any suggestions?

Reply:

Steve, a "Buffeting" effect and noise can occur in HVAC systems where a variable speed fan is installed, occurring when the fan turns on.

Under-sized ducts or too much flexing in ducts, or too-loose flexduct runs can add a "spring-like" effect to the duct system that can make the buffeting problem worse.

I've also read that a too-dramatic transition between duct sizes or diameters can create an obstruction that contributes to HVAC air buffeting problems as will properly matching plenum shapes to duct shapes.

For example installing a square box elbow between two round ducts can cause buffeting.

Those are some things for which to check.

Some HVAC techs apply a "band-aid" by adding an adjustable damper in the duct system but I agree with critics who say that's not finding / fixing the problem.

If the fan speed is indeed variable, try setting it to a lower speed.

 

Question: Vibration noises at scroll / rotary HVACR compressors

2016/06/04 Jim said:
I have a new Goodman, 14 SEER, R22 scroll-compressor, Split-System HVAC unit that was purchased/installed in 2009 but not put into service and started until today.

The unit cools my home very well however the condensing unit is very noisy and has a great deal of vibration in the low side refrigerant line and the condensing coil is physical moving about a lot inside the housing in perfect time with the vibration.

The ambient temperature was/is 105F with the HS press @ 250psi and the LS Press @ 78psi which yields an evaporator coil temperature of around 43F.

The pressure readings are stable with no fluctuation what-so-ever. I am a certified tech with over 25 years of experience and I have never seen a unit do this before now. Anyone have any experience with this problem and/or any advice? Thanks a bunch, Jim

Reply: studies report analysis of vibration in rotary compressors or scroll HVACR compressors

Jim

Look first for loose mounting bolts or screws anywhere on or in the compressor/condenser unit; also look for refrigerant tubing left un-insulated and in contact with a vibrating service. You probably already know those common noise sources and have perhaps more field experience than I do, so let's think and argue about this a bit.

Only a mechanical movement can cause vibration; we can probably exclude outside influences such as wind or nearby mechanicals on other systems;

Is the pad level and secure?
Can you take a mechanic's stethoscope and check components for vibration: seems to me we have either the compressor motor or the fan motor. I don't think that even a bad control such as a relay or TEV would vibrate at such a high frequency as to cause the noise you describe.

I'm speculating you'll trace the noise to the compressor motor itself: perhaps a sticking valve. I did some research on vibration in rotary compressors: you'll want to use Google Scholar to search for and find these articles:

Also

The presence of these and other research papers to me as a non-engineer, suggest that vibration in rotary or scroll HVACR compressors is a known and studied problem.

For a catalog of different sorts of HVAC noises and what they may mean,

see NOISES, HVAC SOUND DESCRIPTIONS - Five groups of HVAC sounds, listed alphabetically from Banging to WuWuWu help track down the noise source & suggest repairs.

 

Question: outside air conditioner or heat pump is making funny sounds

(Mar 7, 2015) jr said:
my outside heat pump is buzzing and the fan is not running

(June 6, 2015) Dale said:
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?

(July 8, 2015) Nelson said:
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 28, 2015) Benny said:
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?

Reply:

Benny:

Bent fan blades,
Worn or damaged fan bearings
Bent fan drive shaft
Loose fan mounts

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

 

Question: air conditioner making noises like a wood chipper

(Aug 10, 2015) dave said:
my unit was making noises like a wood chipper and it wasn't coming from the fan blades or motor.

i checked around the unit and the pushed big hose (electrical wiring) that connects to the condenser that goes into the circuit breaker. it started to spark inside the unit…

i immediately shut the ac off and pushed the wires into the unit more and the noise stopped afterwards. my question is do i need a technician to come out and see if there's a wiring problem or do you think the problem is fixed? it seems to be running fine now…

but i'm worried that there's some miswiring inside somewhere.

Reply:

Dave

Well I'm glad you shut off the sparking electrical components.

But just pushing wires into a unit is not a safe repair.

Electrical wires that are damaged or not secured against movement can be expected to move again, short, and possibly start a fire or electrocute someone. So yes my opinion is that a repair is needed. I'd shut down the equipment until it's fixed safely.

 

Question: periodic BANG from my air conditioner keeps me from sleeping

Aug 26, 2015) Noise in HVAC unit said:

(Aug 26, 2015) Barrianne@gmail.com said:
sorry, didn't add my email
Hi all, 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.

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

 

Question: vibrating roaring sound, then loud rattling knocking sound

(Sept 14, 2015) Anonymous said:
My air when it comes on it makes a sound like a vibrating sound roar then it stops

(Sept 26, 2015) Kelly said:

The air handler in my FL townhouse is making a loud rattling/knocking sound for 3 or 4 seconds about every 3rd or fourth time the compressor kicks in. The A/H sits right outside the bedroom door, and it makes sleeping difficult.

The A/C tech says it is refrigerant surge and is caused by a bad install design. The compressor sits in a platform on the ground level and the air handler is on the third floor. (bottom floor is garage.) Refrigerant lines go up into the attic and down to the air handler.

Tech says even a whole new system may not fix it as the units aren't designed to push the liquid up 3 floors. There are over 100 units in the complex, but I haven't heard anyone else having this issue. Any solution?

Reply:

I would ask for help from a senior HVAC technician on-site. You've answered the question yourself: if it were a design issue then every installation of the same design at your townhouses would behave the same way.


...

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Or see HVAC SYSTEM NOISE DIAGNOSIS FAQs-3 - more-recent questions and answers about noise in heating, air conditioning, or venting systems

Or see these

HVAC Noise Diagnosis Articles

Common HVAC Failures that Cause Noises

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HVAC SYSTEM NOISE DIAGNOSIS FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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