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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 Q&A-5
FAQs on causes & cures of heating, cooling system sounds

Air conditioner or heat pump noise diagnosis Q&A set #5:

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

We also provide a more comprehensive INDEX to RELATED ARTICLES for this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

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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 2020-01-20 by (mod) - Magic Pak HVAC persistent high-pitched noise.

Right; keep in mind I'm flying blind when I'm not sure what equipment you actually have.

Cooling mode: uses an outdoor compressor/condenser unit;
Some outdoor compressor/condensers are heat pumps; those can provide both heat and cooling, while a straight cooling-only unit just does that.

I think your unit is the latter.


On 2020-01-20 by Samantha

This is very helpful, thank you so much for pointing me in the right direction. I do think you are correct that the burner is running in heat mode, as I recall that the flame was going out when it was -20 during the polar vortex last year.

One question - did you mean to write "you're not using the compressor unit in heating mode"? I thought the compressor was typically used in AC units, so I'm a bit confused by that part.

Samantha said:

- great question. I don't know, but here is the unit

Download from this website:

MAGICPAK PACKAGED HVAC UNIT MGE4 SPECS [PDF] (2018) at inspectapedia.com or contact MagicPak, 215 Metropolitan Drive | West Columbia, SC 29170
800-448-5872 Product Support 866-282-7257 retrieved 2020/01/17 original source: www.magic-pak.com/MagicPak/literature/technical-specifications/M-Series_MGE4_Tech_Spec.pdf

Moderator reply:

Samantha yours is an packaged HVAC system combining an electric cooling unit with a gas heating unit split system.

IF you are hearing a high pitched noise independent of whether the system is in heating or cooling mode AND if the gas burner is running in heat mode (thus you're not using the compressor unit in cooling mode) THEN I’d suspect

- a fan bearing failure

- an air leak

- something else we’ve not thought-of

A service tech can usually spot the problem, often by using a mechanic’s sthethoscope to identify exactly which component is producing the high pitched sound you’ve identified.

On 2020-01-16 by (mod) - Magic Pak HVAC unit making a faint but persistent high-pitched noise.

Samantha

The fact that the noise occurs in both heating and cooling mode needs detailing:

In heat mode is heat being provided by a heat pump - same basic machine that provides cooling - or by a separate electric, gas or oil furnace?

On 2020-01-16 by Samantha

The Magic Pak HVAC unit in my apartment has been making a faint but persistent high-pitched noise. The noise is not rhythmic, it's steady. The noise is present whether the heat or AC is running. I'm looking for help with finding the cause of this noise and fixing it.

It started earlier this winter. When I first noticed the noise, the unit was having an issue where it kept switching off unexpectedly/failing to turn on.

The repair guy replaced the fan - he said there was an electrical issue inside the fan which was causing a safety mechanism to stop the unit from running. Replacing the fan made the unit "run fine" - it switched off and on when I wanted it to.
A few days later, the unit failed again in the same way.

The repair guy changed the pressure switch. This fixed the unit, and the problematic noise went away.
But the problematic noise returned in a few days.

When the repair guy returned for a third time, and when he took the pressure switch out and put it back in, it made the noise go away for maybe a day or so. But now it's back and we are out of ideas about how to fix this noise.

The unit is technically running "fine" but I need help diagnosing and fixing the noise. It is not a normal noise for this unit, which I have had for years. The noise seems to be getting worse the longer I try to run it. The noise is also painful to me (I have sensitive hearing and it is causing me pain).

I need to get this problem fixed as soon as possible. This has proven difficult - so far, the technicians have dismissed the problem because the unit technically runs.

Other relevant info: I live in an area with cold winters - temps have stayed between about 0-35 this the winter.

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.

On 2019-12-08 by Chris

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 2019-09-09 by (mod) - AC turns off before it reaches the set temperature.

No Lisa that doesn't sound normal; I suspect that the system has a malfunctioning control, possibly a refrigerant metering valve, and perhaps the system is sensing an abnormally high refrigerant pressure on the compressor outlet side - that could shut the system down.

Let me know what your service tech says - that will help other readers.

On 2019-09-09 by Lisa

AC turns off before it reaches the set temperature. Also new Lennox system and we've owned it for 2 years at first heat pump unit outside was quite now it sound like a pressure is being released when the unit shuts off. Is this normal? Never did it before.

On 2019-05-09 by Helen Short buzz sound

Short buzz sound. AC tech replaced a part but sound is still happening

Short buzz sound

On 2019-04-24 1 by (mod) - clicking sound, directly above the air filte

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.

On 2019-04-24 by Chanda

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 2019-10-26 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.

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 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 2019-08-03 by Vernon

Thank you

On 2019-08-03 by (mod) - loud grinding noise when it kicks off

sounds like a hard starting motor of bad fan motor; or of course something else.

Take a look at the AC noise diagnosis articles above were we offer diagnostics for common causes of many sounds.

On 2019-08-03 by Vernon

My Carrier heat pump makes a loud grinding noise when it kicks off, and it's only 2 years old. It's been doing it since I had it. What would cause that?

On 2019-07-24 by (mod) -

Re posting w/o prohibited advertisement.

Ara Lowel said:

I found this blog to be very resourceful and well written.

On 2019-06-26 by (mod) - low to fast “drum beat” or a sound like filling up your car windshield washer reservoir

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

On 2019-06-25 by Tom

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 2019-06-06 by (mod) - diagnosing causes of BANG sound at compressors

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.

On 2019-06-06 by Darrel J. Hebert

outside compressor makes one bang sound when it shuts down. The sound is like someone would hit it once with a steel hammer.

On 2019-05-29 by Pat

Just had new air handler put in attic for heat pump system. Sometimes now when unit shuts off we hear like a knocking in the wall. It is like the pipes are knocking. It happens in the later afternoon.

On 2019-05-16 by (mod) -

I posted your recording at

HVAC NOISE-2 CHATTER CLANK FAN GROAN - chatter, clank, clunk, cyclical sounds, fan noise, groan, growl, gurgle sounds

under "clanking" sounds - please take a look.


On 2019-05-15 by (mod) -

JB you can use the page top or bottom CONTACT link to send us the .wav file for a listen and for posting here; unfortunately the Comments Box code will allow attaching a photo but not a sound file.

The fact that you observe noise just at night - presumably in cooler temperatures may be diagnostic as is the "noise only when the unit isn't blowing air" - perhaps during a defrost cycle or perhaps a failing motor.

On 2019-05-15 by JB

Lennox Heat Pump. Added a *.wav file with the noise that comes from the air handler. Is coming from the refrigerant line. The unit can run all day and usually not make any noise, but at night will make the noise with great frequency, and the noise isn't quiet. Only get the noise when the unit isn't blowing air. Otherwise the unit cools great.

On 2019-05-02 by (mod) -

The Louver door is probably the easiest suggestion. Alternative route to duct in return air through a wall floor ceiling.

About buzzing noise, you need to pay close attention to discover whether it's a simple mechanical noise like a loose component or a loose compartment door or whether the buzzing is from an electrical component or motor.

On 2019-05-01 by Ellen Siers

We had a new Trane AC system installed with Varialble Air Handler. It buzzes constantly-Why??
Also we were told we needed to get a louvered door to allow more air flow. Wish I had been told this at purchase time! Is there anything that can be done in the closet to improve air flow?

On 2019-02-23 by Greg P

I have heat Pump System. The outside unit starts making loud banging noise, feels like metal heating metal. Thought it is the fan but after HVAC guy check it up was not the case. The issue is that you never know when that loud bang noise will start. Sometimes the heat will be on for 5 hours and the banging will start, sometimes just 20 minutes. HVAC technician changed the Relay, but it did not fix the problem.

On 2019-02-21 by (mod) -

I'll give your question more thought Michelle but off hand I'm stumped. Typically over-charging refrigerant most-risks damaging the outdoor compressor/condenser unit or TXV or reversing valve.

Perhaps the technician will try a mechanic's sthethoscope to track down the specific part that's making that knocking noise.

On 2019-02-20 by Michelle

New Carrier HVAC system installed. When charging the heat pump they overcharged it and blew out the TXV. Ever since there is a very loud knocking noise inside the home that happens for 3-7 seconds right after the heat pump shuts off. It doesn’t happen every time but it does happen more times than not.

No consistent factors, e.g., temperature, thermostat setting, etc. in the 12 weeks since the botched install they’ve done the following to try and fix the issue but nothing has stopped the noise: replaced the TXV again, replaced the entire coil system, installed a solenoid valve, replaced the entire heat pump. Any thoughts on the problem?

My precious system was also a Carrier but I never had this noise or any odd noises until they installed the new system. No one else I’ve spoken to has heard of this before either.

On 2019-01-10 by TJ

Newly installed airconditioner/heat pump makes a thumping sould when it kicks on. Hear it inside the house.

On 2019-01-04 by (mod) -

Lindsay

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.

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

https://inspectapedia.com/plumbing/Water_Hammer_Noise.php 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.


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.

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