Ice formation aroud the expasion valve

[mostafaabdalla4]

what are the reasons that may be cause ice formation only around the expansion valves in central system screw compressors ?

[Grizzly]

Simply put, the fluid (Refrigerant) inside is colder than the air in contact with the outside surface of the expansion valve.
If sub zero evap temps apply then the water in the air will freeze on the surface of the valve.
Basic stuff really!
Grizzly