Thanks for the advice. I knoe soldering aluminum is tough because it goes from solid to nothing in a flash.
Years ago I worked at a factory that had some form of epoxy. I don't know what it was, but I had a friend that had an aluminum coil that was leaking and I put this over the spot and his air conditioner still works after fifteen years or more. This epoxy was made for their metal switch gear, it wasn't your average store bought mixture. Plus what really helped is that I used a vacuum pump on his lines until the epoxy dried. So instead of just covering the hole, I'm sure some got sucked in to plug the small hole.
My leak is where the aluminum tubing was welded to the aluminum shell. I might put a vacuum on and melt a bead along the edge. It is such a small leak. I used the machine for months and it was fine. I couldn't find it with soap and bubbles. I found it when I submerged it in my pool. There was a bubble every ten seconds, only if the coil was pitched. Standing up, sometimes it leaked, and other times it did not.
I haven't submerged the other coil yet. I'm hoping it is a copper leak.
