Black Death, as A/C techs know it, is a result of the breakdown of the refrigerant-lubricant. This causes excessive wear inside the compressor, and the extreme wear causes a black residue that is a combination of solder flux from the condenser and aluminium shavings from the old compressor. When this sludge cools, it hardens in the condenser. Repeated flushing will not remove it. However, when the system is charged and running i,t liquefies, flows out into the liquid line and clogs the orifice tube. With less refrigerant flowing, past the orifice tube, the compressor is starved of lubricant and will lock up. The only answer is to replace the condenser.