What can we do about our noisy Air Conditioner? Can we build a shelter over it?

I agree with Snow Bunny.

A little experience, years ago, my dad bought a window air conditioner and installed it. Whenever it ran it sounded like a freight train going up hill. One day during routine cleaning I asked why there were springs under the mounting bolts. Suddenly he realized the compressor was supposed to be shock mounted (that is to say, the springs were not meant to be fully tightened down). So after loosening them so the compressor could move freely (but not fall off) the noise was gone.

When the unit was shipped the mounting bolts are meant to be tightened completely down, preventing any movement during shipment and preventing damage. However, upon installation it was meant that those spring mounts were supposed to allow the compressor some freedom of movement, thus eliminating any noises.

Same is true for some major appliances like washing machines and refrigerators. You have to remove some shipping pin or something that prevents damage during shipping.

I'm wondering if you have a similar situation. Either the mounting bolts are too tight or there was some shipping strap or pin that was not removed. Normally AC units aren't supposed to be loud, at least not as loud as you are suggesting that it's keeping your neighbor up at night.

Look into that.

But I still agree, you must keep free air movement through the coils or the unit won't work properly, and likely burn out early.

Good luck.

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I find it difficult to believe that a condo complex does not have a standardized and adequate central air system in place. I would pursue this avenue and forget the window units.

Any "shelter" that you may build cannot have any sides. Those would impede the airflow & your A/C will not last long.