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
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.
Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.
A/C & Heat Pump System Noise Diagnosis & Repair Noises: How to Diagnose Air Conditioner Compressor, Fan, Refrigerant Piping, Ductwork Noises
(Feb 3, 2014) Eileen said:
Fog horn sound seems to be coming from roof (started only after men added a cushion to a fan- spring object (?) ) and roofers replaced roof. Others have said no it's not from the roof but they haven't checked it. Goes off every 15-23 minutes day and night and lasts only seconds but noise level rises and drops. It's driving a 90 plus year old crazy and she can't take it anymore (she suffered a concussion from a fall). She also hears large fan from garage (carbon monoxide clearer) but nobody seems to know what to do?
Eileen you may be able to make some progress in discussing this sound with the HVAC repair folks by keeping a log that records and correlates the noise with the operation of the rooftop equipment.
(Feb 6, 2014) Lee Albro said:
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?
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.
(Feb 20, 2014) Greg said:
I have a Parker 9,000 BTU split unit with a blown compressor. A "tech" here in Costa Rica swapped out blown compressor or a newer, undamaged compressor from a 12,000 btu floor unit. He also swapped out the capacitor, sizing the new capacitor correctly to the new compressor. The a/c starts, blows cold but consistently rattles/vibrates loudly after a half hour and then completely shuts down due to excessive heat at the outdoor unit. Any ideas as to what the problem may be? Help please!
SHUT DOWN the system immediately then come back to read more.
Now, take a look at noise group 4 in the "More Reading" links just above.
I wanted you to turn off the unit because if it is suffering from an over-charge or excess refrigerant, or if the refrigerant metering device is not working properly the liquid refrigerant can cause "liquid slugging" which basically destroys the compressor.
With that concern in mind you want to be sure that the right quantity of refrigerant (and correct type) was installed.
While you're at it check for loose mounting bolts too, but I'm guessing its an improper charge or a problem with the refrigerant TEV (thermal expansion valve) metering system, or something else that we're not smart enough to guess at by text-comments.
Keep me posted
Thanks Daniel, you are the man. Now I have some info to go with.
(Feb 24, 2014) Jim Dinsdale said:
We are hearing a intermittent humming, that turns into a pounding "wum, wum" noise through the wall that connects our stone cottage with our neighbour. She has an air source heat pump that runs her hot water and central heating. The noise can go on for hours with what sounds like a motor starting up, revving up at about 180 beats per minute, then reaching speed, then after a minute or two fading away for a few minutes before starting again. It can happen anytime day or night but is most distressing at night, typically occuring from the early hours until about 9am or later. I would be grateful if you could suggest what this might be. Our neighbour says she can hear the noise but denies it is coming from anyhting in her house. We had no problem until she had the system installed three years ago, and on several occasions when we have complained, the noise has stopped for a few days.
The first step in an issue like this noise problem is to obtain an impartial and reliable witness to document the problem and its apparent source. What you describe might be a piece of equipment with a failing control or motor - like a heat pump fan or compressor motor. It's no surprise that people's hearing ability varies widely as does their ability to tell direction of sound.
(Apr 2, 2014) Sandor Lipschultz said:
40 y/o Payne furnace: after burners come on, buzzing sound from fan compartment for 20-30 sec. and then burners go off; on/off furnace switch fuse blows
Buzzing is often a bad relay switch. Sounds as if there may be a failed motor or control. An overcurrent when a motor can't start-up can be the cause of blown fuses.
(Apr 18, 2014) Charles said:
I am suffering from fan ventilator noise, i.e., loud humming, that's operative 13 hours a day 7 days a week. I need to find a way to block the noise. I can't hear myself think, and apparently the Department of Public Health feels the decibel level is "legal." What to do?
Assuming you've checked with your doctor or audiologist and are sure there is no medical issue involved and that the noise is for certain traced to the fan you mention, it would make sense to start by determining if the equipment is functioning normally and properly. Fan motor noise, including humming, could be an indicator of a hard-starting electric motor that in turn indicates a risk of burn-up that in turn could be a fire risk. So have a qualified technician check out the equipment.
If it is determined that the noises that bother you are normal equipment behavior, then you'll want to review our article series on sound control in buildings, beginning at
(Apr 21, 2014) PP said:
I work in a research lab and we're using a split system to do some tests. We recently moved out of our lab space and so we had to remove all the refrigerant charge from the system and then charge the system again in the new space. I've charged this unit before (just trimmed the charge 10% to 40%), but I've never had to charge the system from scratch. I've been having some problems with this-
I've added around 70% of the refrigerant charge to the system but I still don't see an increase in the subcooling. The subcooling is -68 C (:-/), the pressures are way way below the normal pressures, the EEV is wide open and there's no bubbling in the sight glass.
The compressor recently started having start up problems. It starts and then stops (Scroll compressor).
Am I looking at liquid floodback in the compressor?
How long do I need to run the unit before I see an increase in the pressure? There's been no increase in the pressure since I first started charging.
If you are in any doubt about liquid flood-back, stop the system immediately. The result of liquid entering the compressor can be its destruction.
Normally we see the system pressures changing immediately as the compressor begins to run, reaching a stable HIGH and LOW side pressure after an interval that may be quite a bit longer: 10 minutes to 20 minutes in my experience, depending on the system size, cooling area addressed, heat losses and gains, ambient temperatures. On commercial refrigeration systems I sometimes left a cooler running overnight to stabilize before checking again the next day.
That arm waving complete, if the system does not include a refrigerant receiver in its design it needs a precisely accurate refrigerant charge to work properly. Even with a refrigerant you need to be close. The actual refrigerant quantity you need depends on not just the equipment as purchased from the manufacturer, but also the lengths and diameters of the refrigerant piping installed too - as that volume has to go into the calculation.
You'll need to get the charge right by adding the required volumes and charges together, starting with the manufacturer's spec. You may know that a refrigerant charge procedure also has to consider the temperatures at the time of charge.
(July 2, 2014) Sandra said:
Roaring noise is Terrible! We have a small condo with one main return duct. The unit sits in an exterior closet room off patio, but abuts the wall that the return vent is in, and there is not much room between the unit and the wall vent.
Is there ANY POSSIBLE way to muffle this loud roar to a more tolerable level??? It's SO loud you must turn the tv up extremely loud just to hear what's being said, and then it's crazy loud when the system rotates to "off" when temp reached inside. You can't carry on a normal conversation when the system turns on, winter or summer, AC or heater!
HELP - please?!
Sandra in NJ
Duct insulation, duct isolation mounts, air handler isolation mounts can all reduce HVAC noise transmission, but for the unusually loud noise you describe I would ask FIRST for an evaluation by an experienced HVAC repair technician, as it's possible that your equipment is not working properly, possibly not safely.
(July 5, 2014) Ginger Vela said:
Hi Dan, I have a York 19 SEER AC unit that is very efficient, but it developed a rumbling sound from the air handler like low, rumbling thunder when it comes on. At first it was slight but has grown longer over time. It continues for anywhere between 15-30 + seconds and then goes away.A tech came out to do regular service and, wouldn't you know, it didn't act up, so he did not hear it. It seems to do it less when I have it set colder than I like it.
Since thunder comes from cold air meeting up with warm, I thought maybe that had something to do with it. Probably crazy. Please help so I can share your thoughts with the next tech I might call. Otherwise, it is running well. Bought it in 2009, and it had a defective compressor which had to be replaced in less than 2 years from purchase. Only I was able to hear the noise of that compressor dying. Thank you.
Interesting problem: rumbling noises from an air handler.
I'd start by looking with care for loose components: loose blower mounts, motor mounts, ductwork, vibration dampener.
Don't forget to check for loose blower fan assembly itself.
FYI, the cause of real thunder, in the outdoor air, is not quite cold air meeting warm. More accurately, the lightning bolt very rapidly heats a small column of air to very high temperatures. The thunder you hear is the noise of the rapidly expanding air. Horizontal and forked lightning may make a longer rumbling sound.
Hi Dan, Thank you so much for your prompt and helpful suggestions. I'll be able to speak intelligently about possible causes with a technician. My inclination has been to wait for it to get worse only because when the compressor died, no one could hear the agitator-like sounds that I did before its last gasp. Hopefully, it won't get any worse or louder. Thanks again, Ginger Vela
Hi Dan. I'll be sure to let you and the readers know whenever I get an answer to the rumbling in my air handler. It has been getting gradually worse, but I've not yet called in the technician again since the unit works so well otherwise and is very efficient. Thanks again, Ginger
(July 18, 2014) Marie said:
I have a new 3T 14 SEER gas/electric package unit installed on the roof. When I started the AC for the first time, it doesn't sound like any AC I've ever had before. It sounds like a sump pump and initially blows hot air before the cooler air comes out of the vents. Is this normal?
(July 24, 2014) Adrienne Keen said:
Hi my air conditioner motor ( outside ) is leaking an enormous amount of water when it is first switched of What can be the cause of this Please Help Thank you
Sounds as if the AC condensate is not being routed to a drain and properly drained away.
for diagnostic help
8/10/14 PKG said:
Hi , The compressor on my 3 Ton Amana A/C unit starts after 5 minutes of fan start ( there is no delay relay ) .. cold air blows out from top of the unit ..
and looks like compressor tries to start couple of times and finally starts on 3-4 try and then it works normal ..
Any advice will be appreciated.
Sounds like a hard-starting compressor, possibly a failing compressor motor, possibly aided for a time by a hard-start capacitor kit.
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