Can anyone tell me what is the difference between TEV with MOP and TEV without MOP? What is MOP?Also i've install a new TEV onto the coldroom and the hissing sound was at the liquid line?I've check the pressure on low and high side.the charging looks fine.One strange thing was,only one pipe at the evaporator is icing up and it melts after few minutes.Is it that the orifice is too big which oversize?

Pls Help??


Thank you

Jeff