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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 & Cure
Evaluate Air Conditioner / Heat Pump Compressor, Air Handler, Ductwork Noises

  • POST a QUESTION or COMMENT about air conditioning or heat pump system equipment or control or ductwork noises: cause, significance, cure

Air conditioner or heat pump noise diagnosis & cure:

HVAC systems can produce a stunning range of noises many of which can help lead quickly to the trouble source and thus can help tell us what repair is needed.

This air conditioning repair article 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 shrieking and howling or death-rattles that sometimes (not always) presage costly compressor damage indicating air conditioning compressor or A/C compressors at or near end of their life.

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A/C & Heat Pump System Noise Diagnosis & Repair Noises: How to Diagnose Air Conditioner Compressor, Fan, Refrigerant Piping, Ductwork Noises

In the A/C system noise diagnosis article below we discuss how we approach listening to and interpreting noises coming from an air conditioning or heat pump system.

Topics: how to diagnose & repair noises or sounds traced to HVAC systems including compressor/condenser units, air handler units, air conditioners, heat pumps, furnaces, ductwork, motors & controls. Recordings of HVAC system noises.

Categories of sound by HVAC system sound type & what the sound signifies.

Article Series Contents

This article discusses how to diagnose & repair air conditioning compressor noises from the compressor/condenser, air handler, duct work, filters, or controls

Photograph of an old burned-out air conditioning compressor unit

If your air conditioning or heat pump system has lost its cooling capacity or won't start

see REPAIR GUIDE for AIR CONDITIONERS.

See HOW to DETERMINE COOLING CAPACITY of air conditioning equipment if the system seems to be working but is inadequate to cool your building. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

First question in diagnosing HVAC system noises is where are the noises coming from?:

Second question in diagnosing air conditioner or heat pump noises & sounds: what does the noise sound like?

Air Handler & Ductwork Noise Diagnosis & Cure for HVAC Systems

How to Diagnose & Fix Noises at the Compressor/Condenser & Condenser Fan Unit

If you hear unusual noise at the air conditioning system, these compressor sounds could indicate the need for a simple service and adjustment requirement.

But air conditioner compressor noises might also mean that you face an upcoming costly repair involving replacement of the compressor itself. You should have the system checked promptly by an air conditioning service technician.

The following is a list of air conditioning compressor noises and what they may mean about the operation, condition, and remaining life of the cooling system equipment.

I have a National comfort Products CPO 2464-B unit which is an air conditioner and gas heating unit combined.

The unit is about 5 years old. The air conditioner had become increasingly noisy. I called the party that installed the unit. After spending $90.00 for a service call I was informed the the external coils were dirty, opening up the unit light was not visible thru the coils.

I was advised to use a garden hose and rinse the coils. I did not have that available so I turned the unit on and using a watering can, poured warm soapy water onto the coils. this was done several times. the unit now seems to work properly. I did not see this particular problem described on your website.

There may be other means of cleaning the coils but this was all I could think of. - C.A.P., Norristown PA

How to Diagnose Noises at a Split System Air Conditioner / Heat Pump Indoor Wall-Mounted Unit

Fujitsu has offered some helpful advice in troubleshooting noises that may be heard at the indoor wall-mounted air handler of a split system air conditioner or heat pump. What's particularly helpful is that Fujitsu points out that some noises that people worry about are actually normal and not an indication of trouble. Quoting [3]

Here are some other noise or sound diagnostic clues for split system air conditioners & heat pumps

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-07-26 by (mod)

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

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

- use of a mechanic's stethoscope

On 2020-07-26 by Rick

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

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

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

On 2020-07-03 - by (mod) -

Tony

Some possible sources of AC compressor/condenser unit noises are at

https://inspectapedia.com/noise_diagnosis/HVAC_Noise_Diagnosis.php#Comp COMPRESSOR NOISES

Please take a look and let me know what you think.

On 2020-07-03 by tony

Very loud noise when compressor is running - reduced cooling. Can shut off system and turn back on couple of minutes later - no noise and unit appears to be cooling ok. after running awhile - compressor becomes very loud again

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.

On 2020-06-01 by Lorrie

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 2020-05-17 - by (mod) -

I want to help but don't have enough information to offer more specifics than to try to narrow down the noise source; Perhaps a mechanic's stethoscope can help.

On 2020-05-17 by Jdags

Not sure exactly as I am having trouble locating it, but it seems that the indoor unit is making a weird compression-like sound when starting then intermittently.

Sometimes it sounds like it's inside, sometimes it sounds like it's outside, sometimes it sounds like it's coming from the electrical panel...I know, weird!
Thought it might be hard start condenser, so I changed it. No luck...

On 2020-03-26 - by (mod) -

Speculating, TJ that could be a hard-starting compressor (motor is failing).

On 2020-03-24 by TJ

My brother had 2 carrier units [5 ton/flr 1 & 3 ton/flr 2] for both Heat & AC installed in Sept 2019. Both are single speed compressors and everything from heater [NG], evap coil, air handler, plenum/etc were all replaced. The unit in questions is the 3-ton that services the upstairs

Over the last 7-10 days, upon turning on the upstairs AC, he has heard a loud rumbling sound for about 15 secs from start-up, then it seems to dissipate and smooth out. His son's room is right under the unit and he was over w his kids Saturday. When he turned on the unit, he said the wall kind of vibrated while the 15 second rumbling took place. My brother has heard it 3 times in 7-10 days, but he has to be in the vicinity of area to hear it.

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

Stan,

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

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

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

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

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

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

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

On 2020-01-26 by Stan

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

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

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

On 2020-01-20 - by (mod) -

Samantha: our entire conversation about Magic Pak HVAC unit in my apartment has been making a faint but persistent high-pitched noise. is now found at

https://inspectapedia.com/noise_diagnosis/HVAC-Noise-Diagnosis-FAQs5.php


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