HVAC Noise Diagnosis FAQs-2

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

HVAC Popping Hammering Noise FAQs

Jackhammer noise out of one of our A/C ducts

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. - 2017-07-02 by Manoj

Reply by (mod) -

Manish

I would start by finding just what. Equipment is starting up at that time. When the noise is only at one of many ducts in the system I suspect loose ductwork or metal ductwork with large unsupported flat metal sections that are vibrating in response to air pressure.

Heating units make popping noise at startup

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. - (Jan 25, 2016) Michelle

Reply:

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

 

Straining Noises at HVAC Systems, FAQs

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 noisy 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.

 

Inside air handler unit vibrating noise diagnosis starting point

Inside unit 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? (May 3, 2016) Aj

Reply:

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

 

Air buffeting noise problems in HVAC systems: Cause & Cure

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? (May 27, 2016) Steve

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.

 

Vibration Noises at HVAC Equipment, FAQs

Vibrating roaring sound, then loud rattling knocking sound at A/C unit

My air when it comes on it makes a sound like a vibrating sound roar then it stops - (Sept 14, 2015) Anonymous 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? - (Sept 26, 2015) Kelly

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.

Vibration noises at scroll / rotary HVACR compressors

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 2016/06/04

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:

Research on Vibration at Rotary Compressors

• Imaichi, Kensaku, M. Fukushima, S. Muramatsu, and N. Ishii. "Vibration analysis of rotary compressors." (1982). - you can read this directly at docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1406&context=icec it's very technical, but the conclusions are worth noting. It makes me want to check the stability of the voltage being delivered to the unit; if that's ok it makes me suspect the motor itself is bad.
• Kim, Dae-Kyong, Kwang-Woon Lee, and Byung-Il Kwon. "Commutation torque ripple reduction in a position sensorless brushless DC motor drive." Power Electronics, IEEE Transactions on 21, no. 6 (2006): 1762-1768.
• Ishii, Noriaki, M. Fuhushima, K. Sano, and K. Sawai. "A study on dynamic behavior of a scroll compressor." (1986).
• Lee, Ho-Jung, and Kwang-Joon Kim. "Multi-dimensional vibration power flow analysis of compressor system mounted in outdoor unit of an air conditioner." Journal of sound and vibration 272, no. 3 (2004): 607-625.

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: vibration noise after fan replaced

I had my fan replaced on my outside condenser , heat pump. Now, there is more noise and vibration than before, I had to put foam between top grill and frame. It is a 4 ton unit and he put in a 1/2 HP 1075 rpm motor. He said it is because my last motor was a piece of crap. Does this sound like the right size motor. thanks 2016/09/15 Steve said:

Previous question error. He put in a 1/3 hp motor, not 1/2 hp, thanks

Reply:

Perhaps more noise and vibration from improper mounting or an unbalanced fan blade set? Look for loose parts first.

Unless the fan is running at the wrong speed, I would not expect fan vibration and noise to be due to motor size.

 

Very noisy and vibrating new Goodman Split System HVAC unit - expert tech seeks more info

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 On 2016-06-04 by Jim

Reply by (mod)

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:

Imaichi, Kensaku, M. Fukushima, S. Muramatsu, and N. Ishii. "Vibration analysis of rotary compressors." (1982). - you can read this directly at http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1406&context=icec it's very technical, but the conclusions are worth noting. It makes me want to check the stability of the voltage being delivered to the unit; if that's ok it makes me suspect the motor itself is bad.

Also

• Kim, Dae-Kyong, Kwang-Woon Lee, and Byung-Il Kwon. "Commutation torque ripple reduction in a position sensorless brushless DC motor drive." Power Electronics, IEEE Transactions on 21, no. 6 (2006): 1762-1768.
• Ishii, Noriaki, M. Fuhushima, K. Sano, and K. Sawai. "A study on dynamic behavior of a scroll compressor." (1986).
• Lee, Ho-Jung, and Kwang-Joon Kim. "Multi-dimensional vibration power flow analysis of compressor system mounted in outdoor unit of an air conditioner." Journal of sound and vibration 272, no. 3 (2004): 607-625.
  
  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.
  

Followup by Jim

Thanks for the response and insight. The unit has quieted down significantly over the last 24 hours of operation with the condenser coil assembly now not having nearly as many moments in movement/vibration. These moments are also now more in synchronization with the enclosure movements.

The only changes I have made so far is in three (3) small refrigerant charge reductions based on superheat readings at the compressor return inlet.

I suspect there was/are possible refrigerant condensation fallout occurring inside the low pressure return line despite the pressure readings being stable with only very small fluctuations indicated in the high side discharge line.

The HS head pressure and LS pressure ratio is well within declared limits stated in the manufacturer's setup specification documentation.

I am considering adding a liquid line-trap loop in the low pressure piping near the evaporator outlet to see if it makes any difference in the vibration. I will post my findings. What is your opinion on my thoughts and direction? Thx, Jim

Reply by (mod)

Interesting; check that nothing remains loose.

Indeed refrigerant on the low side, as you know better than I, can at worst ruin a compressor and less bad, might cause ugly noises. Interesting and clever thing to try - slight charge reduction. Thanks for keeping me posted; working together makes us smarter.

Question: copper refrigerant pipe vibration noises indoors

I have two HVAC systems with heat pumps. The copper pipe (heat) that comes out of one unit vibrates alot and causes noises in the house.

It is an upstairs unit and I had the vibrating pipe ran up outside the house, into the attic and down to the upstairs unit.

It still vibrates and makes noises. Is there something that can deminish the vibration after it leaves the unit and before it reaches the house? (Feb 6, 2014) Lee Albro said:

Reply:

Lee, that vibration doesn't sound good - as it can cause a wear-leak, refrigerant loss, heat loss, or other equipment damage.

You could install foam insulation around the piping (it should be insulated anyway) where it passes through openings or needs buffering, but I'd suggest asking a service tech to diagnose and fix the vibration - hoping to avoid a more costly problem.

Air conditioner making noises like a wood chipper, FAQs

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. - (Aug 10, 2015) dave

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.