minichopper has too much charge and your freezing up the evaperator thats why the amount of air goes down. then since your not evaporating refrigerant the low side pressure drops too lower and kicks the low pressure switch. put a manifold gauge on the low side when it happens and i bet youll see the saturation temp of the refrigerant below 32 degres hell youll probebly be far lower.. way too many people overcharge these systems let some out. screw the ozone layer