What is the high side pressure? The ideal situation is when the evaporator develops a thin skim of ice just before the compressor cycles off. As the ice melts, it absorbs quite a lot of BTU's in the process. It sounds like you don't have enough pressure drop across the evaporator as the liquid from the condenser converts itself to gas as the refrigerant makes its way through the evaporator. That refrigerant evaporation is what cools the air passing over the coil. Monitor the temperature drop of the air as ir passes through the evaporator- - - -it should be dropping 15-20 degrees, minimum. Adjusting the refrigerant pressure by tinkering with the charge weight, and running as low an evaporator fan speed as possible to give the air plenty of time for heat exchange will give the best cooling.
Jerry
