Black Death occurs when certain compressors run too hot and seize. In the process, melted teflon gets into all parts of the system. This teflon has the interesting characteristic that when cold it sticks to hoses, condensor, evaporator, etc and therefore cannot be flushed.
So the unwitting owner replaces the compressor and drier, has the lines flushed and the system charged for $1500 or so. Then after it runs for a while, the teflon liquifies and apparently turns to black goo, which gets sucked into and clogs the new compressor. Hence the term Black Death.
Steve - Did I get this right?