System Floodback

System floodback is caused by low superheat. The liquid refrigerant makes its way
back to the compressor while its running. If the refrigerant cannot boil off in the evaporator it
will work its way back to the compressor and the oil in the compressor will become diluted
and it will wash the oil off all the surfaces to the point where you have metal on metal at the
load bearing surfaces like the drive bearing and bushing in a scroll and main bearing in a
semi hermetic compressor.
 

What Causes Refrigerant Floodback:
• Damaged Metering device
• Oversized Metering
• Incorrect placement of TXV bulb or external equalizer
• Dirt or debris in metering device
• Wrong superheat setting
• Low Evaporator loads from poor air circulation
• Dirty filter, fan blades or coils
• Sudden changes in load like hot gas defrost or condenser fan cycling

How to prevent Liquid Floodback:
 

• Make sure you have a minimum of 20F/11K superheat at the compressor
• Have properly sized metering device for the evaporator
• On capillary tube or fixed metering device applications make sure the system
has a proper refrigerant charge
• Using a suction accumulator will protect the compressor
• Always make sure you maintain adequate air flow in the evaporator
• How to check if you had floodback on Semi-Hermetics pull of the pump house
and see if the crankshaft moves up and down a lot, if so you had floodback.