Flooded Starts

Flooded starts are caused by liquid refrigerant sitting in the crankcase with the oil
because of refrigerant migration. Refrigerant migration occurs anytime refrigerant, and oil
are in contact with each other, and the compressor is not running. The refrigerant will
travel from the evaporator and move through the system as a vapour and condense in the
compressor oil. The oil will float on top of the liquid refrigerant and when the compressor
starts up the refrigerant explodes up out of the crankcase. Refrigerant is a good solvent
and will wash oil off all the surfaces and cause metal on metal. For Scrolls you will see
damage inside the scroll set but minimal damage to the drive bearing and bushing. For
Semi Hermetics you could have the oil pump seized on or a seized rod on the crankshaft.
 

Things that affect refrigerant migration:
 

• Length of time the compressor is off
 

• The ambient temperature around the compressor

How to prevent Flooded Starts:

• Install and use crankcase heaters anytime that ambient around the compressor
gets below 55F/12C because if the refrigerant wants to migrate to the coldest
part of the system and if the compressor has a crankcase heater that will reduce
the risk for flooded starts.
 

• Locate or relocate the compressor in ambient that will not cause migration
 

• Maintain an optimum refrigerant charge because there is something called
refrigerant to oil charge ratio. You may have all the above checking fine and you
still have flooded start issues, it could be the refrigerant to oil charge. Its a
refrigerant to oil charge limit for manufactures. The more refrigerant and the less
oil amount will result in more migration.
 

• Use a pump down cycle so all the refrigerant is removed from the low side of the
system.