Where are they checking for leaks? If you're losing freon, you have a leak. It doesn't just disappear.

I don't know what a smoke test is, but usually you put freon with die in it into the system. The dye is visible with a black light, so you fill it up, run the AC for a while and then look for the die at likely leak locations.

Are they checking the evaporator? Search the forum and you will find high numbers of posts about evaporator failure. Hopefully, it's just a leak in a connection or something.

You can get the freon with die at Wal-Mart and do it yourself. I have never had to do it, but there are probably instructions posted by someone here or over on Volvospeed.

Good luck!