Recently purchased a sweet lime online, and it was doing fine until I had to move it around a bit. It was in the line of my air conditioning unit and it was causing neighbor plants to drop leaves as well.

The lemon tree seems to have recovered, and the lime was doing fine until it started dropping leaves like crazy. The leaves appear to have brown spots on them, and those still on the tree are not brown but rather have lightened patches that turn brown when dropped. If a leaf is about an inch in size, the brown patch is about a third of it. There doesn't appear to be any fungi or visible pests I can see. Five inches away, my Meyer lemon is growing happily, so I would imagine anything that affects citrus uniformly would bother it too. Any suggestions for recovery?