Have them check it & tell you where the leak is coming from-depending on what they find-the fact that they say it is low not empty rules out them putting a hole in a line, condenser or breaking a tube which would probably leak out completely. Have them put dye in it, partial charge & leak test. It would also probably be best to wait around & watch till they can show you the place where it is coming out. Let us know. (another scenario is that was low before taking it in but still cooling but now compounded by an electrical problem to a/c clutch or something that they could have done)
