Flooding occurs when liquid refrigerant enters the compressor cylinder instead of gaseous refrigerant, causing internal damage and potential catastrophic compressor failure. The compressor is designed to compress only refrigerant vapor; liquid refrigerant is incompressible and causes connecting rods to bend, valves to break, and cylinders to crack. Liquid slugs traveling at high velocity destroy internal components on impact.
Causes and Prevention
Flooding results from low evaporator temperatures dropping below 32 degrees Fahrenheit, causing complete refrigerant vaporization failure, or excessive refrigerant charge exceeding system capacity by more than 15 percent. Thermostatic expansion valves or electronic metering devices failing in the open position allow unrestricted refrigerant flow into the evaporator. Dirty filter-driers restrict flow and cause temperature drops that enhance flooding risk.
Detection and Recovery
Symptoms include low superheat readings below 5 degrees, compressor noise and knocking, and oil foaming visible in sight glasses. Technicians stop the system immediately and perform an evacuation and recharge with proper superheat verification between 8 to 12 degrees at the evaporator outlet.
System Restoration
Flooded compressors require replacement. System flushing with approved solvents removes metal debris and contamination before reassembly.