[Killer Bee]

uv dye injection, our guys have found some odd leaks that way..

one that comes to mind, the seams of a compressor housing leaking, tough one to find otherwise..

evaporator leaks are tough too, but dye will usually work it's way down the condensate drain and let you know..

lots of kits out there, one's I buy for the shops are green plastic folding case from grainger..

sure there's a bunch of youtubes showing how it's done too..

good luck!