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Old 06-24-2020, 02:32 PM   #1
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Why is my AC unit sometimes noisy?


Sometimes, usually it seems after it has not been running for a while, the AC unit makes a vibrating/buzzing noise. I've tried to pinpoint what part of the unit it may be coming from, but can't identify a source.

If I turn it off with the thermostat and then start it back after a couple of minutes there is no noise.

I have a short video clip of the unit while it is making the noise here...

https://drive.google.com/file/d/1mKE...ew?usp=sharing
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Old 06-24-2020, 03:23 PM   #2
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Re: Why is my AC unit sometimes noisy?


Compressor sounds really bad. Possible it's not bolted down and just vibrating too much, but I doubt it.

A question - cabinet has "407c" written on it.

Did you have it converted from r22?

If it was converted without doing something to ensure oil return, the compressor is probably damaged.

(changing to poe oil, using an addictive or topping off with poe oil)

407c is not compatible with the mineral oil used in most r22 units.

I'm only speculating and you'll have to have it inspected in person to determine the source of the noise.
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Old 06-24-2020, 05:18 PM   #3
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Re: Why is my AC unit sometimes noisy?


I didn't have any conversion done, but I did just have the compressor replaced. It's brand new. And the noise was happening before the replacement also, so I feel safe about ruling it out.
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Old 06-24-2020, 05:29 PM   #4
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Re: Why is my AC unit sometimes noisy?


I’d say that compressor isn’t well.
Or the charge isn’t right.
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Old 06-24-2020, 07:36 PM   #5
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Re: Why is my AC unit sometimes noisy?


Sounds like this is not the first compressor failure since this system was converted from R-22. That's a sign that the system wasn't converted properly and possibly too much mineral based oil was left in the evap and lineset. That can be why this compressor is also failing. It actually sounds like the bearings are damaged from lack of lubrication.

Normally the tech will have told you what he thinks went wrong with the compressor he replaced. If it was a burn out (hermatic motor electrical wiring fried), did oversized suction line filter get installed? If it failed with internal mechanical problems, such as complete lock up or hammering noise, he should have taken special steps to ensure that the system didn't still have lots of mineral oil retained and in need of a clean up procedure.

I think you will get a chance to talk to him pretty soon from the way that unit sounds.
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Old 06-24-2020, 07:50 PM   #6
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Re: Why is my AC unit sometimes noisy?


Might want to clean the condenser coil.
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Old 06-24-2020, 07:51 PM   #7
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Re: Why is my AC unit sometimes noisy?


Tell the tech to consider this: The system may be circulating goo formed from the cross contamination of the oil types and that is causing it to go through cycles of wide pump down type swings that cause the crankcase oil to foam and make the compressor noisy from partial slugging. That's what it sounds like to me after I listened through several runs of it.

It'll require a clean up to fix and that'll be extensive (and expensive)... even going as far as removing the compressor and dumping the oil and then removing the metering device and circulating the proper cleaner charge through the lineset and evap. Then ditto for the condenser coil after cutting the lines free. Then replacing the liquid line filter/drier and installing a suction line filter just for good measure. Then a recharge with virgin gas since the old reclaimed gas isn't usable. That's the way it should have been done in the first place. Hopefully the compressor isn't damaged yet but time will tell.
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Old 06-24-2020, 09:13 PM   #8
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Re: Why is my AC unit sometimes noisy?


I believe the newer r22 compressors have poe oil and a litte left over mineral is not big deal.

If the compressor in this unit is bad, best to scrap the entire unit.
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Old 06-24-2020, 09:42 PM   #9
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Re: Why is my AC unit sometimes noisy?


Quote:
Originally Posted by beenthere View Post
Might want to clean the condenser coil.

Good call. I've looked at the video a couple of times, granted my eyes are old but I can't see the fan spinning.
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Old 06-25-2020, 05:11 AM   #10
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Re: Why is my AC unit sometimes noisy?


Quote:
Originally Posted by 57TinkerMan View Post
Good call. I've looked at the video a couple of times, granted my eyes are old but I can't see the fan spinning.

It may not be spinning. Hard to tell on some vids and with some units cause of how well the gard covers the blades.
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