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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 Repair FAQs-4
Q&A on causes & cures of heating, cooling system sounds

Air conditioner or heat pump noise diagnosis Q&A set #4:

This air conditioning repair article series discusses the diagnosis and repair of heating sytem or air conditioning sysgtem noises.

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A/C & Heat Pump System Noise Diagnosis & Repair Noise FAQs

Photograph of this ugly duct routing risking water entry, mold, rodents, high operating cost.These questions on finding and curing noises traced to heating, ventilation, or air conditioning systems were posted originally at NOISES, HVAC SOUND DESCRIPTIONS - be sure to review the diagnostic advice at that article.

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 2019-01-04 by Lindsay

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 2018-09-30 by (mod) - do not bypass the circuit breaker

Carmen

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.

On 2018-09-28 by Carmen

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 2018-08-23 by (mod) - mouse-damaged components caused banging noise at the compressor

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

On 2018-08-23 by Brian

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 2018-06-15 by (mod) -

Could be a buzzing relay
see HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing, thumping

On 2018-06-15 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?

On 2018-06-1 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.

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

On 2018-06-14 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?

On 2018-06-14 by (mod) - 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?

On 2018-06-13 by Sid Thunder

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 2018-05-12 by (mod) - faint noise like tornado warning sirens

Jon

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

On 2018-05-12 by Jon

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

On 2018-02-27 by (mod) - sounds like it has something metal flapping in the duct

Bob

I'd look for loose components or insulation in the HVAC system.

Watch out: if duct components are drawn into a blower fan it can jam, overheat, and could risk a fire.

On 2018-02-27 by Bob

My air handler sounds like it has something metal flapping in the duct when it is on?

On 2018-01-14 by Deandrade 24/7 humming noise and a water running

An unknown, denied and hidden cooling equipment running inside the apartment bellow mine controlled by cell/remote device from outside/inside a car. I hear a 24/7 humming noise and a water running for 3 seconds every 3 minutes.

The system speeds up with bang and whistle and a second stage starts sounding like a 747 for about 20 minutes. Slowly, fading away, it goes back to the humming. Several inspections had been made but the AC, when turned On/Off from the wall thermostat, is regular showing no noise nor vibration.

Inspection shows Pure Tone 126/55, Structural Noise. Immediately after a power outage, the system jumps at its highest level showing, as recorded, 59.6DBA. It is every where, however,inside bathroom is worse. The neighbor is a very intense person with a compulsive behavior and having control over the system and denying it gives him power.

Whatever is there is connected to the unit on the roof and runs inside central system. Any suggestion?

It seems that it is nobody's responsibility, Association, police, City representatives...

 


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

Or see HVAC SYSTEM NOISE DIAGNOSIS FAQs-5 - more recent Q&A about diagnosing the cause of noises on air conditioners, heat pumps, heating systems

Or see these

HVAC Noise Diagnosis Articles

Common HVAC Failures that Cause Noises

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HVAC SYSTEM NOISE DIAGNOSIS FAQs-4 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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