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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8769
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a split ac unit. The unit inside is making a loud

Customer Question

I have a split ac unit. The unit inside is making a loud humming noise. Any idea what that could be?
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.


Tell me if the system is cooling and heating OK or not... and about how old it is. And if the humming is steady and constant or intermittent or changes pitch.

We can go from there.

Customer: replied 1 year ago.
Hi Phil,
The system is heating and cooling okay as far as I can tell. The sound is intermittent and the system is around 11 years old.
Expert:  Phil replied 1 year ago.

Thanks, we should do some basic maintenance first.

Tell me if you have ever cleaned the fin and tube condenser coil that surrounds the outside of the unit.

Noise testing is done by feeling for the vibration with your hands, you can generally feel the source, if that fails you can use a mechanics stethoscope ($25 or so at an auto parts store.)

We keep going until we get the cause sorted out.

Customer: replied 1 year ago.
I've had previous work performed on the outside unit but not sure whether or not the fin and tube condenser coil was cleaned.
Customer: replied 1 year ago.
How do I clean it? I am a female so the parts to the until are a new language to me, so if you could describe what I'm looking for, that would be a great help. :) Thank you in advance for your patience.
Expert:  Phil replied 1 year ago.

Hello again,

That video is on the topic of cleaning the condenser coil.

Remove the covers, and use tape to hold the blower door switch closed.

use a heavy wooden cooking spoon to press on various parts of the inside unit until you can feel the vibration, be careful not to poke the spoon into the spinning blower wheel.

And tell me how far you have to get away from the unit before you can barely hear the humm.

Note: The 24 volt control transformers tend to humm gently, thats normal,

Those are pictures of typical 24 volt transformers.