Rear suspension height system

The car has been riding low for several months before I decided to take a look. I was trying to see the ride height sensor so I could perhaps buy another. I removed the driver side rear wheel to access the sensor. All seems connected okay. There is a small bolt on the connecting arm and I noticed that it was adjustable, no more than 3/16 inch or so, and moved the arm as far as it would move it down. I didn't do anything else mechanically. I put the wheel back on and let the car down. Miraculously the car was sitting up where it should be! Overnight the car settled back down. I got in the car, turned the key on and I heard the compressor lifting the car to the height it should be. So, I'm thinking there's an air leak. I'm about half deaf so how can I check for air leaks in that system? Thank you so much for your site.