AC unit makes loud screeching noise?

Hello,

Just to clarify, the noise you hear is under the hood.
If so, then it is likely the belt that is making the noise under the load from the A/C compressor.
Usually glazed belt can make this type of noise, as it will slip on the pulley and create that screeching noise.
Inspect the belt for wear and any glazing.

Here is a helpful guide:

https://www.2carpros.com/articles/car-squeaking-noise

Worn belt needs to be replaced to fix the issue.

https://www.2carpros.com/articles/replace-serpentine-belt

Please let me know of any questions.
Thank you.