HVAC Noise Diagnosis FAQs-2

Q&A on HVAC Noises
Hammering, Straining, Vibration, Wood Chipper Noises

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.

 

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.

 

VIBRATION NOISES at HVAC SYSTEMS, FAQs