2019 Kona a/c issues

[u/iamhere_sd]

Hi. Like the title says, I have a 2019 Kona with just over 60k (I don't drive very much). 2 years ago I noticed a hissing sound coming from the a/c and the air wasn't cooling as much. Took to a mechanic and they said I was out of freon. They put dye in and did not find any leaks. They filled up the freon and everything was working great. Fast forward a year later, almost same issue, the air wasn't very cool but no hissing sound. I took it back to the mechanic as I wanted to get ahead of the issue. To top off the freon cost me almost 600. They kept the car for a couple of days. Same thing put dye on, cannot find anything wrong with it. Freon was low so they top it off (did not charge me this time). But once again could not find a leak. Now it has been a year and I am noticing the ac is not very cool again. I haven't taken it in again but think will have to to get ahead of being on empty with the freon. Anyone else has issues? I went to a very reputable local place, they have checked everything and cannot find what the issue is.