Hello all,

I'm bothered by a little piece in my A/C that makes a coil whine sound when switched off, and the sound changes but still is present when turned on. I know capacitors can be glued, but for this piece I'm not sure, since it's encapsulated in a plastic box. If anyone has an idea that would be greatly appreciated!

 

It is a buzzer, an audible alarm to indicate a fault condition.
The A/C operating manual would indicate the conditions when the alarm is to be activated.

 

Hello,

The shown part could well be the humidity sensor.
Here is an example:
https://electropeak.com/hr202l-humidity-sensitive-resistance-sensor-module-with-case
It will not be the source of the heard sound.

Bertus

 

I agree with bertus. Unplug the module and see what happens.