When flooding of the evaporator takes place, frosting along the suction line will be evident. This is caused by the liquid refrigerant boiling off and reducing the temperature of the suction line. Frosting along the suction line can also occur when there is a pressure drop through the evaporator and the suction line temperature is reduced to below 0o C
With low temperature applications the returning suction vapour may be at a temperature well below 0o C resulting in suction line frosting. It is common practice to insulate suction lines of low temperature installations in order to overcome this problem.