Got call for walk in freezer down. Arrived to find coil iced up and evap fans not on. Found DTFD bad. Thawed out coil replaced and left. About 4 hours later manager sends me back saying box won't drop below 30F. Get back and coil is completely iced up again. Thaw out coil turn unit back on. With in an hour evap coil has a large amount of frost on it. Sight glass is clear, evap coil clean, evap fans check out good, comp passed the pump down test. Solenoid valve is in condensing unit, its opening up all the way. Unit takes r408a. Larkin condensing unit model Dpa-1/2l5-ep68. Larkin evap coil model ep68-2.Out of defrost suction pressure is 23 which is -8f coil, head pressure is 250 condenser is clean. Box gets down to 27f, checked suction line temp is 26f. Superheat is 34. Tried opening up valve after an hour and half of opening valve up 2 full turns, coil has large amount of frost on it again. Put unit into defrost to thaw out again and start over. I'm thinking my TXV is bad unless I missed something?