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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 & Cure FAQs-3

Air conditioner or heat pump noise diagnosis & cure Q&A set #3:

More FAQs about the causes & cures for heater, air conditioner, heat pump, or other refrigeration system noises to help tell us what repair is needed.

This air conditioning repair article series discusses the diagnosis and repair of cooling or heating system noises and sounds of all sorts.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

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 2018-11-05 by (mod) - my heat pump short cycles on and off when in heating mode

Vickie

I am sorry that I can't offer a specific diagnosis but frankly we just have too little information to say anything useful beyond the compressor failure articles listed right at the end of the article above.

I would call an HVAC service technician for on-site diagnosis and repair help.

But before doing that, also take a look at our description of the common causes of air conditioner or heat pump "short-cycling" on and off, found at

SHORT CYCLING AC COMPRESSOR inspectapedia.com/aircond/Air_Conditioner_Short_Cycling.php

On 2018-11-05 by Vickie

This summer AC would not coolin very hot days. On the heat, when unit starts it runs for 5-10 seconds and then stops

On 2018-10-18 by (mod) - wooing sound of air conditioners

Gee, Alex, I honestly don't know. Could you describe "wooing sound" a bit more. Surely the AC isn't making affectionate noises.

See HVAC NOISE-5 SCREAM SING TRUMPET WHINE WUWU - scream, sing, squeal, trumpet, water sounds, whine, whoosh, whistle, wuwuwu, or silence

for more detailed diagnostic advice.

On 2018-10-16 by Alex wooing sound coming from new rheem AC 14 seer non variable speed.

What is cause of wooing sound coming from new rheem AC 14 seer non variable speed.

On 2018-09-24 by (mod) -

if your technician has ruled out all mechanical noise sources such as those that might be related to a blower fan or it's driving Parts, another thing to check would be the thermostatic expansion valve

On 2018-09-23 by BJ

I had a new unit installed in April. Still cool here that time of year so we were using heat. When it warmed up and we turned the ac on, we started hearing a loud pitch squeal. It only happens late at night/early morning. Typically between 1 and 6 am. It happens in between cycles.

Not directly before or after startup. It comes from the component that's in my crawl space (I'm not too sure what it's called).

I've tried different things to try to get it to stop and have figured out that it only squeals when the thermostat is set higher than the outside temp or close to the outside temp. In other words I have to have it set much colder than the temp drops at night.

For example, I have it set to 68 starting at 9pm.

Last night the temps dropped to 67. Woke up to it squealing this morning.

The installer cannot figure out what it is. He replaced the brand new blower motor thinking that's what it was. Didn't help at all. Any ideas? It's about to drive us crazy!

On 2018-08-21 by (mod) -
Diagnose the humming sounds by following the clue frrom your HVAC guy:

Jeff

Diagnose the humming sounds by following the clue frrom your HVAC guy:

Look at what electrical equipment might be running or trying to run.

A motor that is having trouble will often hum - before it burns-up or fails.

Search InspectApedia.com for ELECTRIC MOTOR DIAGNOSIS or for HARD START CAPACITOR to understand more about that possibility.

Of course replacing an air filter won't mean much to a failing blower motor, but maybe the tech figured as long as she'd gone to the trouble to look at the system she might as well do something useful.

See HVAC NOISE-3 HISS HOWL HUFF HUM - hiss, howl, huff, hum, groan, woo wuu wuff or humming noises

On 2018-08-21 by Anonymous

@Jeff R, Also, turning the furnace off at the thermostat does not make the noise stop, nor switching form cold to heat..

On 2018-08-21 by Jeff R

Randomly, around 1AM there is a humming sound that starts out low and ends high (lasts about 1-2 minutes). It is not reproducible, the HVAC guy replaced the filter on the first trip, blower motor on the second but it continues. I recorded it this morning at 120AM, it sounded strongest around the whole house humidifier area.

On 2018-08-14 by (mod) - Flowing air doesn't sound like running water

I'm baffled myself Ryan. Flowing air doesn't usually sound like running water - perhaps there is something loose in the ductwork.

Or you could be hearing condensate running down a disposal drain.

On 2018-08-14 by Ryan S

No sir, I opened the HVAC closet and no noise like that coming from refrigerant piping. Another thing I just noticed, when you open the HVAC closet, you get a rush of freezing air coming out, like that closet is super freezing. And the air coming out of the vents isn't near as cold.

On 2018-08-14 by (mod) -

check and tell me if they're running water sound is associated with refrigerant piping

On 2018-08-12 by Ryan S

My townhouse has floor vents, the first few vents closest to the A/C Unit have a very loud rushing water sound coming from them. Like loud enough that it sounds like a rushing stream lies beneath my floors.

Our largest unit, is a 50 pint and it produces anywhere from 150-250 pints of water per day.

I'm still training in Home Inspection and i'm stumped on the water running sound. My landlord isn't very quick to respond to problems here, so that further complicates things.
Any suggestions on the running stream noise?

On 2018-08-10 by (mod) - air conditioner banging noises

Allie

Let's start with the diagnostic suggestions for air conditioner banging noises at

On 2018-08-09 by Allie

My AC unit indoor will run for awhile then start making this banging noise even though it’s not cooled to desire temp yet. It’s like it shuts off and is trying to start back up. Unit is only 2 years old. Help!

On 2018-07-09 by Kim humming noise

Apartment next door neighbor whom I share a wall with. Their heater in winter and now AC in summer has a very low frequency variable humming. The hum goes faster then slower with speeds in between. It's like a wah, wah, wah, wah faster slower. My ceiling along the wall we share vibrates (felt by placing my hand on the ceiling).

It's a long wall, the length of my living room. I can hear the hum in the other parts of my apartment, not as loud as I move away from it. It drives my insane and is irritating, I want to scream. Tried to talk to property manager about it.

All she did was say that's apartment life! and then went on to tell me how her unit faces the other direction and street where car alarms are always going off.

My unit's AC/heater is very quiet. Don't even know it's on, except for feeling the heat and cool air. So, I KNOW my neighbor's unit variable humming is not normal. I have been researching and would like some ammunition (evidence) to speak with her about it again that it's not normal, even though she says it is.

On 2018-04-24 by (mod) -

Ruth


I'm a little concerned with the noise you're describing could be due to liquid slugging which can damage the compressor. I would prefer to turn the system off and call your service company for an inspection and repair.

Let me know what you're told and I may be able to suggest follow-up comments or questions.

On 2018-04-24 by Ruth

Trane not trance. Damn spell check :)

Trance is a little over a yr old and makes a knocking noise after it shuts off.

On 2018-03-11 by (mod) - Outside unit hums on start

Sounds like a hard-starting compressor.

On 2018-03-11 by Pap

Outside unit hums on start up about 2 seconds and then runs normal.

On 2018-01-15 16:54:17.718145 by Cindy

We have Quietside split AC unit. The outside unit has started making a humming noice but the inside units work. The outside fan is also still working. Any ideas?

On 2017-12-13 by (mod) - buzzing noise repair

Bryan,

Please take a look at the description of a common sources of buzzing noises given near the top of NOISES, HVAC SOUND DESCRIPTIONS. That would be the best place to start

On 2017-12-12 by Bryan W.

My indoor A/C handler is making a loud buzzing noise when the heat is turned on, the noise starts as soon as the heat kicks on and ends when the heat kicks off.

I'm pretty sure my system has a heat strip if that helps. What should I be looking for if I remove the front plate of the handler to take a look inside?

On 2017-12-10 by (mod) - banging noise repair

John

Start with the Banging Noise diagnosis descriptions found at

https://inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions.php#Bang

On 2017-12-10 by John

The outside blower unit makes a loud Noise when it shuts off. Almost sounds like a bad bearing. It occurs more frequently in the colder early morning hours. What needs to be done to correct it?

On 2017-11-03 15:10:02.690438 by (mod) -

Christine,

First let's figure out what sort of equipment you have installed.
Does your home use forced warm air heat?
Does your home have only air conditioning or is that unit also a heat pump that provides heat in cold weather?

Also check the settings on your thermostat: is it set to HEAT COOL OFF or what?

On 2017-11-03 13:26:35.698183 by Christine grantham

When my outdoor air conditioner is shut off and the temperatures outside drop, the air conditioner makes noise in my house. What could be the problem with the air conditioner? Thank you chriselen1@msn.com

On 2017-10-26 18:52:03.093467 by colben

Air running for 2hrs then stop the cold the inside fan start making noise

On 2017-08-16 15:32:01.528650 by (mod) -

Robert

I'd distinguish between loose parts or a motor that's unable to start. Both need service, but a humming motor is headed for a burn-up and needs immediate repair.

On 2017-08-16 14:44:01.213312 by Robert Godin

My new heat pump makes a low humming and oscillating noise that is very annoying. What could that be ?

On 2017-07-29 03:47:12.074042 by Jami

My Ac unit is making a chirping noise like a bird after it is turned off I still hear a chirping sound it comes and goes

On 2017-07-05 14:11:03.899154 by (mod) -

Sounds like a condensate drain problem. Id take a closer look as we dont want a spill that might invite a mold problem.

On 2017-07-05 11:40:50.284856 by Angela h

It's like a sucking noise

On 2017-07-05 11:40:16.644331 by Angela h

There is a noise like water coming from the unit under the house. My air is fine though. Is something about to break

On 2017-06-19 22:57:27.899784 by Aaron

Recently while my AC is running a have a random "noise" coming from the basement where the blower is. My best description is it sounds like a large truck engine brake. It's brief and occasional. There has also been a quick "bang" "chirp" noise. It sounds like when the fan is going to a different cycle. I can't see to narrow it down. It's louder when I'm upstairs than when I'm actually sitting right next to it. It's a Goodman and 1 year old

On 2017-05-21 18:58:24.632521 by (mod) -

Angel

Whistling is often a problem at an expansion valve or sometimes a more serious overpressure problem at the compressor.

We discuss the common causes (and cures) for whistling noises at an A/C compressor in HVAC Noise Group 5 at https://inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions_5.php please take a look and then don't hesitate to ask for more help.

Danile

On 2017-05-21 18:30:18.767260 by Angel

Hello guys!
I got a 4ton unit that is making a whistle noise at the compressor side it starts after like 10min from starting the ststem but it doesn't shut the ststem off, it sounds like the safety valve on any compresor i can hear a small whistle, if i shut off the system and wait a minute or 2 i turn it on and it goes away for another few minutes! My question is if this is a sign of a problem or its normal? If this is a problem what can i look for? Thanks in advance for any help given

On 2017-05-19 20:06:17.876893 by (mod) -

Sorry, I'm not sure what handle you are asking about. If you mean a circuit control board, then you would need to know the manufacturer, model number, and serial number of your compressor condenser unit, and then contact the manufacturer to get the part number if you don't already have that information.

With a part number it should be pretty easy to find a price both from the manufacturer and from your local HVAC suppliers

On 2017-05-19 18:31:31.810739 by David

Can someone tell me about the interior AC compressor panel and why it would be missing, and what it would cost to replace?

On 2017-05-15 16:16:29.538595 by (mod) -

Ralph:
You've done one of the good steps in tracking down the source of an annoying noise by turning things off. Here are some more considerations:

A neighbor's mechanical system or equipment could be running, so more turn-off diagnosis could help

Metal ductwork often makes noises like those you describe as the ducts expand or cool: sheet metal clunks and thumps. Those sounds are usually most noticeable near the start or after the end of an HVAC system turning on or off or its blower fan turning on or off.

If you have not done so be sure to read
CLANKS CLUNKS from air conditioner or heat pump system - found at inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions_2.php#Clank

Track down the noise to its source by careful listening, with helpers, in various locations to see where sound is loudest.

Try using our NOISE LOG (search InspectApedia using the search box above) to relate noises to weather, temperature, time of day, etc.

On 2017-05-15 by (mod) - squealing noises at the A.C.

Cindy, squealing noises at the A.C. unit have several causes and vary in importance. Details are at

inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions_5.php

On 2017-05-15 by Ralph S

I'm at my wits end over this.... I moved into a 20 year old condo two years ago.

I'm on the third floor of a four story building. Intermittently, I hear a clanking noise that sounds like someone throwing a tennis ball against a cement wall.

I hear the noise throughout my entire apartment because the noise is coming out of my A/C vents. I even hear the noise if all my power is turned off.

On 2017-05-15 by (mod) re: clanks, clunks, noises like tennis ball tossed against a wall

Ralph:
You've done one of the good steps in tracking down the source of an annoying noise by turning things off. Here are some more considerations:

A neighbor's mechanical system or equipment could be running, so more turn-off diagnosis could help

Metal ductwork often makes noises like those you describe as the ducts expand or cool: sheet metal clunks and thumps. Those sounds are usually most noticeable near the start or after the end of an HVAC system turning on or off or its blower fan turning on or off.

If you have not done so be sure to read
CLANKS CLUNKS from air conditioner or heat pump system - found at inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions_2.php#Clank

Track down the noise to its source by careful listening, with helpers, in various locations to see where sound is loudest.

Try using our NOISE LOG (search InspectApedia using the search box above) to relate noises to weather, temperature, time of day, etc.

On 2017-05-15 14:48:25.888371 by Ralph S

I'm at my wits end over this.... I moved into a 20 year old condo two years ago. I'm on the third floor of a four story building. Intermittently, I hear a clanking noise that sounds like someone throwing a tennis ball against a cement wall.

I hear the noise throughout my entire apartment because the noise is coming out of my A/C vents. I even hear the noise if all my power is turned off.

On 2017-05-15 by (mod) re: where to go to find squealing noise sources in HVAC systems

Cindy, squealing noises at the A.C. unit have several causes and vary in importance. Details are at

inspectapedia.com/noise_diagnosis/HVAC_Noise_Descriptions_5.php

On 2017-05-12 by Cindy

*live in Florida

A.C. Unit making loud squealing noise. So I shut it down. Love in Florida on fixed income .

On 2017-04-16 by (mod) re: bad start run capacitor

Sue

That may be a bad start/run capacitor that gets the fan going; search InspectApedia using the box above to find our article on HARD START CAPACITORS for MOTORS

On 2017-04-16 by Sue

Main fan motor making whirring noise been having difficulty spinning on its own

On 2017-03-10 by (mod) re: refrigerate mode vibration

I'm not sure, Sandra, what "refrigerate mode" is. But if the tech was referring to a defrost mode or any other HVAC equipment mode, that still would not explain excessive vibration. Something is wrong.

I agree that checking for loose parts is a place to start. But now it sounds as if you want to call the service company, talk to the service manager, and ask for help from a more senior, experienced service technician.

On 2017-03-10 by Sandra

Inside Carrier unit in attic sounds like it's gonna vibrate out the roof on occasion. Then the vibration becomes slight? He Ck for lose parts I thought it was falling apart. He said it maybe going thru refrigerate mode? I've had it checked over n over tech can't find anything. It's serviced 2 times yr always.

On 2017-02-25 by (mod) re: wind gusts as sources of regular-interval building noises

Anon

I would look again at mechanical systems. It's just not reasonable that wind gusts would occur at regular intervals and be of regular lengths.

On 2017-02-24 by Anonymous

Moved into new construction 3 floor SW facing condo and have an intermittent, "fan like" noise which is unpredictable , lasts precisely 12 minutes, is not related to fans being on or off, is located in the ceiling area of the dining room on north side of condo and is heard in next door condo .

Builder says it is caused by "wind gusts" getting in the vents and there is nothing he can do about it. He has never heard the sound. The noise does not necessarily occur when it is very windy , when it is colder and is not heard when the fans are turned on in the condo. What is this?

 

On 2016-12-15 by Becky

My new Hvac makes a "farting" noise when it starts and stops. Any Suggestions?

On 2016-09-21 by (mod) re: horrible clanking rattling noise inside an air handler

I suspect your fan or blower assembly has a failing belt or the fan assembly bearings have failed; SHUT OFF the system, call a repair tech, and do let us know what you're told. Daniel

On 2016-09-21 by Colen

Ac on The inside is making a horrible loud noise like it is clanking and rattleing

On 2016-08-12 by (mod) re: popping, rattling, roaring, rumbling, running water sounds from air conditioners

Anon in the live links near the top of NOISES, HVAC SOUND DESCRIPTIONS you might enjoy reading

HVAC NOISE Group 4 - loud start, popping, rattling, roaring, rumbling, running water

where we discuss causes and cures of rattling noises.

What you describe might just be a loose part, or on the other hand, a motor that's vibrating (and on the way out) could be shaking the outdoor unit.

On 2016-08-12 14:32:29.876812 by Anonymous

I have a Fujitsu split unit in my garage. Recently it has started making a rattling noise on the wall unit. It will go away while I touch it on the side (actually on a piece of plastic) but when I let go, it makes the same noise. It will eventually go away for a while but then happen again. I don't see anything loose on it. Please help.

On 2016-07-07 21:54:29.358166 by (mod)

Mary,
Start with your local building department about location requirements.

Even direct rooftop mounting does not prohibit sound isolation methods.

Also from your description the equipment may not be working properly and may fail soon.

On 2016-07-07 16:35:57.389808 by Mary Hale

Above my condo are 3 large condensers that service a restaurant on the ground floor of the building. I can hear 2 of them come on and off. One has a nearly continuous buzz / hummm sound, the other one has more of a motor sound, almost like a small plane that wants to take off. This is summer in Florida, so they are on virtually all of the time. Builder tells me that due to hurricane code they must be mounted directly on the roof. *they are over my bed room! Is there any help for this? thank you ~ Mary

On 2016-07-06 20:30:20.325186 by (mod)

Eric in the article NOISES, HVAC SOUND DESCRIPTIONS you'll find live links in caps at this text

Buzzing sounds (also crackling) at electrical components anywhere, including compressor relay switches, electrical connections at any component, and quite seriously, at circuit breakers can be an indication of arcing and an electrical problem needing prompt attention.
See BUZZING sounds from A/C or heat pump.
Also
see ELECTRICAL SYSTEM NOISES.

On 2016-07-06 03:31:16.985833 by Eric

what would cause a unit to just make a buzzing sound when turned on

On 2016-06-06 17:04:58.310123 by (mod)

Leave the system off pending repair to avoid an electrical hazard.

On 2016-06-06 05:58:11.292184 by Lynn

After turning unit off inside We straight away turned the unit off at main switch outside as we are going away. Made a loud hissing noise. Tried turning it back on to no avail.

On 2016-06-05 15:09:32.201863 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.

On 2016-06-05 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 am 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

On 2016-06-04 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.

On 2016-06-04 01:06:44.701276 by Jim

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

Question: copper refrigerant pipe vibration

(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?

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.

 


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HVAC Noise Diagnosis Articles

Common HVAC Failures that Cause Noises

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