# Whistling Noise From Central Air Conditioner



## JScotty (Jan 14, 2013)

knight508 said:


> Hello,
> 
> Today was a warm and humid day so I decided to fire up the Central AC and I noticed that after about a minute this very annoying whistling noise begins. I asked around and was told that it could be not enough air flow/leaky vent. I mentioned how could that be seeing as the furnace ran all winter without the whistle? (I should also mention this is in a house I recently bought so it’s all new to me). He mentioned that the blower runs faster in AC mode which would make sense as to the difference. I have however opened up all the vents and even temporarily removed the entire air filter and the whistle remained. I don’t think it has anything to do with the blower or the air pressure/vents since I noticed something else. When I manually switch the AC off the blower still blows for about a minute at the same exact speed but the whistle instantly goes away. The same goes for when I turn the AC on. No whistle for about a minute while the blower is going its normal speed but when the AC seems to “engage” is when the whistle occurs. I’m thinking it has something to do with the refrigerant or a valve. Any suggestions/insights? Thanks!
> 
> -Bill


Could be freon whistling through the metering device. I've had homeowners tell me they notice it when the unit gets low on freon. May want to have freon levels checked. If not it could be some kind of a partial restriction at the metering device.


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## knight508 (Sep 8, 2012)

JScotty said:


> Could be freon whistling through the metering device. I've had homeowners tell me they notice it when the unit gets low on freon. May want to have freon levels checked. If not it could be some kind of a partial restriction at the metering device.


Thanks for the reply. As I mentioned I bought the house recently and decided to tidy up the condenser side a few weeks ago and decided to replace the insulation since it was worn. I found this:







http://imageshack.us/photo/my-images/19/1001148to.jpg/
Would that have any effect as well as the possibility of it being low on refrigerant? Thanks.


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## hvactech126 (Nov 11, 2010)

It may make the noise in cooling only because the blower is at a higher speed for cooling. Try shutting the a/c off and running only the fan. Have you replaced your filter lately?


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## knight508 (Sep 8, 2012)

hvactech126 said:


> It may make the noise in cooling only because the blower is at a higher speed for cooling. Try shutting the a/c off and running only the fan. Have you replaced your filter lately?


I temporarily removed the filter and the noise remained. Also, when the the t-stat is set to off and fan manually on there's no noise.


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## biggles (Jan 1, 2008)

refrigerant moving thru the system.especially with the cooling OFF but the fan in on.run the cooling at 65F to keep it on and block the top of the condenser outside so the air doesn't discharge into our face ...garbage can top with a coule of bricks.WHY this...trick:wink: blocking the air discharging will bring the head pressure up along with the suction pressure go down to the furnace and see if the noise is happening...not swet:thumbup:you won't blow the compressor up  just for 5 minutes... also put a screw driver to the insulated line/suction and thin raw copper line/liquid then your ear to it...do you hear anything.


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## knight508 (Sep 8, 2012)

biggles said:


> refrigerant moving thru the system.especially with the cooling OFF but the fan in on.run the cooling at 65F to keep it on and block the top of the condenser outside so the air doesn't discharge into our face ...garbage can top with a coule of bricks.WHY this...trick:wink: blocking the air discharging will bring the head pressure up along with the suction pressure go down to the furnace and see if the noise is happening...not swet:thumbup:you won't blow the compressor up  just for 5 minutes... also put a screw driver to the insulated line/suction and thin raw copper line/liquid then your ear to it...do you hear anything.


 Hi Biggles,

Well, I did exactly as you said and the noise went down quite a bit. Down enough to not hear it from the usual living spaces. Also, I noticed when I put my ear up to the cold line outside the whistling noise is very noticeable regardless of the condenser being blocked. The hotline really didn’t sound like anything. So, what does this mean? Thanks!

-Bill


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## hvactech126 (Nov 11, 2010)

It means low charge.


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## knight508 (Sep 8, 2012)

hvactech126 said:


> It means low charge.


Which means a leak no? Unless it was charged that way initially. The furnace is new and where the location of the evaporator and line set going into the duct I think they could have installed it without even touching any part of the AC. Guess I'll get a tech to charge it up?


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## KENT4 (Sep 30, 2015)

*AC Whistling Sound*

I have a slightly different problem. I get a variety of different whistling sounds that last between 15-45 seconds WHEN THE AIR IS NOT BLOWING. The whistle is either just before the air/compressor turns on or just after it turns off. The whistle is therefore not due to air flow or a filter or an improperly sized duct as it makes the sound when the air is not moving. Anything I can tell the tech to check/look for?


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