Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN NOISES, HVAC
INSPECTION CHECKLIST - OUTDOOR UNIT
LOST COOLING CAPACITY
MOTOR OVERLOAD RESET SWITCH
NOISE / SOUND DIAGNOSIS & CURE
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
Diagnose these HVAC noises: screaming, singing, squealing, trumpeting, water gurgling, whining, whistling, wuwuwu sounds at an air conditioner or heat pump.
Air conditioner or heat pump noise diagnosis & cure: 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 costly compressor damage indicating air conditioning compressor or A/C compressors at or near end of their life.
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
HVAC Noise Group 5: screaming, singing, squealing, trumpet, water gurgling, whine, whistling, wuwuwu sounds
The following HVAC noise descriptions are a continuation from the article beginning at NOISES, HVAC SOUND DESCRIPTIONS
A Hissing or Screaming A/C compressor, also described as "very loud screaming" by some sources , may be caused by excessive internal pressures - a dangerous condition. Compressors include a high pressure sensor that should shut the system down if internal pressures are approaching a dangerous level. But if the compressor continues to run and is screaming, turn it off immediately as the system is unsafe.
Sounds like a whining, singing or rumbling sound coming from the compressor/condenser unit fan motor may be due to a broken internal cooling fan motor part or a vibration set up between the fan blade and fan motor/shaft.
Reader Question: loud squealing, clanking compressor noise
Because I couldn't see clearly in the photo and there was some intermittent clanging, I first thought to check for a fan blade assembly that is hitting an obstruction, is loose on its drive shaft, wobbling, hitting the enclosure. But your note that the noise is intermitten argues against a loose part or assembly.
But ultimately, to me this sounds to me like a unit that is unable to start. I suspect a bad compressor motor or bearing. That cyclic sort of clanging-buzzing sound may be a motor or fan motor trying to start in response to a start relay; the continuous squealing though sounds like a bad motor.
I speculate that during the day the compressor is running continuously in hot weather, perhaps also making the motor itself quite hot. Then finally in the evening as temperatures fall, the compressor and centeral A/C gets ahead of the building cooling load enough to cycle off - but not for long. Trying then to re-start fairly quickly the motor may be unable to re-start against a remaining high refrigerant head-pressure.
Such troubles can be caused by a failing compressor motor, an improper refrigerant charge (less likely), a sticking refrigerant control valve (possible), or something else I haven't thought of.
It's time for a service call by an experienced HVAC tech.
Let us know what your service tech reports - what we learn will assist other readers.
Reader Question on squealing A/C outdoor compressor/condenser Unit
Our compressor started squealing intermittently the other night around 1:30am. Did it for about 2 hours but not consistently nor constantly. drove us and the dogs crazy. hasn't done it since. HVAC tech says it was the compressor bearings and can't fix it since its 20 year old unit. I think that's love. what do you say? - Secn
Normal vs abnormal squealing sounds at A/C compressors Secn: ... "that's love"... is that a new term for B. S. ?? Anyway, there are multiple possible sources of squealing, such as the compressor motor, or even a fan motor. If it's the compressor, it's dead or dying; because the units are hermetically sealed, they're not repairable.
Thanks Dan. yep, wonderful spell check changed from the word I had originally typed to "love". it was a clean word though but B. S. works just as well. hah aha. So, the tech also said it's drawing high amps along with the bad compressor. Would the cap fix this too? He said he can't service anything on it Cruz it is R22 freon and can't be obtained anymore. I know they are moving to the R410a but I still say B. S. - Secn
Sorry Secn but high amps draw means the motor is near end of life. The cap may keep it going a while but it sounds like it's bad news. Tech is also right about the refrigerant. You may be able to install a new compressor, evacuating and cleaning the system (better to do it BEFORE a compressor burnup as a burnup contaminates the piping and increases the later repair cost a bit), installing a new compressor and a substitute refrigerant, possibly having to make some other adjustments, but less costly than a wholesale replacement. Keep us posted. - DJF
Reader Question: hard starting A/C compressor, squealing noises, high pressures: diagnosis & repair
Hello and thank you in advance for any assistance you can provide. My house central air conditioner began to make squealing nosies upon start up so we had a professional repair company come inspect it. It would still start, eventually, after turning itself off and on several timnes, and the cooling still worked great.
The first inspector said he checked coils (they were dirty and my husband cleaned them), capcity, contactor, etc. This person put on a hard start kit, and went away. Well, the problem was still there and in fact worse. We called again, and the company sent someone else who checked more areas and filled up the freon and went away.
Well, it was still starting very hard, with noises, and my husband removed the hard start. He began to check the voltage and wires and borrowed a pressure guage from a good friend who does this for a living. We thought is might be the high pressure shut off switch, but when we started it again last night with the guages on, the high pressue shot up for about a minute and then slowly came down and settled within its stated range.
We sat by the outside unit watching it the entire time of course to shut it off at the switch outside if needed. Again, cooled just fine, but now we have seemed to eliminate the high pressure switch as being bad and we don't know what else to try. Our friend said he has never heard of a unti starting with such high pressure and then settling back down with no issues.
We are of course trying to avoid replacing this unit. It is a YORK, 12 years old, and installed by the builder when we bought this house new. It is a 5 ton unit as we have a dual zone system, which just means it has a damper in the attic unit that directs the flow from one side of the house to the other. Do you have any thoughts on what else to check, what to do, or do we just throw in the towel and buy a new unit? - T & L A, 7/11/2013
Some of this AC squealing and high pressure diagnosis you've gone thorugh is indeed a bit confusing; squealing compressor noise is not likely to be fixed by cleaning the coils - it's more like doing what one knows how to do regardless of the problem.
Typically a squeal means hard-starting which could be a bad compressor motor, bad start capacitor, or a compressor having trouble starting against a head pressure (try leaving the system off for 30 minutes and then re-starting). Similarly, just "adding freon" is not going to fix the problem - "to a carpenter every problem looks like a nail"
Watch out: I would NOT be messing with pressure checks even though you have a gauge; the problem is that without connecting the gauge set to a can of refrigerant and purging the gauge hoses and fittings you risk introducing air into the A/C sytem and messing up its charge or worse, introducing contaminants.
You may be uncomfortable being candid, but you should certainly tell the HVAC tech what you've done so far, so that nobody rules out a messed-up or contaiminated refrigerant charge. Otherwise people could waste still more time and money by not guessing the complete history of the system.
Installing a hard start kit is the first line of attack many techs use as it's quick, easy, inexpensive. When that does not work, a more careful inspection and test of the unit controls, charge, voltage draw during startup, and similar steps are needed for an accurate diagnosis.
I suggest calling your HVAC service company, talk calmly and without accusation (or they'll just go into defense mode) with the service manager, and ask him to send a senior, experienced technician out to test and diagnose your system. Also see the article beginning at the top of this page for some discussion about A/C noises and see http://inspectapedia.com/aircond/AC_Compressor_Hard_Start.htm on hard starting compressors.
Whistling Noise at HVAC Equipment: diagnose whistling at the air handler or compressor/condenser or in Ductwork
Whistling sounds in HVAC duct work or air handlers are often due to air leaks see
Whistling Thermostatic Expansion Valves (TEVs): on refrigeration systems that include a liquid refrigerant receiver and as long as there is adequate level of refrigerant in the system and the TEV is working, the refrigerant charge amount is not absolutely critical.
A whistling TEV means low refrigerant. (You won't hear whistling at a capillary tube metering device).
Listen for a whistling thermostatic expansion valve - a sign of low refrigerant and if you hear that whistling sound see TEV INSTALL & REPAIR
Reader Question: whisting squealing window air conditioner [recording provided]
8/28/2014 I have a window/wall air conditioner that recently started making this very annoying "squealing" sound. It doesn't happen all the time though... In fact, it almost seems to trigger when something else happens (e.g. when the walls rattle or vibrate, or when a door closes, etc) although sometimes it just kind of happens.
The unit is actually mounted in the wall on a chassis and when the noise is active, it's pretty loud inside the house but it's almost non-existent if you're standing outside next to the compressor. The only way I can get it to stop squealing is to smack it on the side a few times, but even with that it still starts to squeal again (at one point or another).
WHISTLING WINDOW AIR CONDITIONER is a recording I made of the sound in case that helps.
Any help / advice is most appreciated. Also, because I rent the place I'm kind of at the mercy of the landlord (which is why I haven't just replaced it myself).
Jeremy a window AC compressor motor that's squealing - if the sound is indeed coming from the motor - would most likely have the same causes as the squealing noises in the article above.
"Typically a squeal means hard-starting which could be a bad compressor motor, bad start capacitor, or a compressor having trouble starting against a head pressure (try leaving the system off for 30 minutes and then re-starting)."
On some air conditioners the noise you describe could on occasion also be traced on occasion to a bad thermostatic expansion valve. The fact that the noise stops when you smack the unit could point in that direction.
I'll post your recording here to encourage other hvac techs to comment further.
Please see GROANING, HUFFING, WUWUWU sounds from A/C or heat pump system, diagnosis where we discuss these noise descriptions together.
Continue reading at NOISES, HVAC SOUND RECORDINGS or select a topic from the More Reading links shown below.
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Question: high pitched screaming heat pump
(Feb 18, 2014) Courtney said:
My heather [sic] [heat pump?] recently began making a low high pitch screaming sound the entire time the heat is blowing, it piercing and started to hurt my ears. I also noticed it made a loud bang just before the heather kicks on. Should I be worried?
I also forgot to put that it makes a tick tick tick sound for about 10 seconds before it kicks on at all. Im sure its an old model i live in a very low rent if that says anything apartment.
Sounds like a compressor having trouble starting. The noises you describe don't sound very safe. I understand it's cold but it would be safer to leave the equipment off while waiting for a service call.
Question: whistling AC at time of turn off
(May 19, 2014) Anonymous said:
My a/c unit is making a high pitched whistling noise when the unit goes off. Any ideas?
we discuss whistling that is often traced to air leaks in the duct system. Let me know if that's your case.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References