A/C compressor oil balancing is a critical step when replacing a compressor. When a compressor fails, some oil remains trapped in other components like the condenser and evaporator. If you install a new compressor filled with its full factory oil charge, the system will have too much oil. This extra oil reduces cooling performance and can hydraulic-lock the compressor. You must drain and measure the oil from the old compressor and match that amount in the new unit.
Incorrect oil balance is a leading cause of premature compressor failures. Too little oil starves the pump, causing it to seize. Too much oil coats the internal walls of the evaporator and condenser, reducing heat transfer and causing the system to blow warm air.