Started with a 4x8 walk-in freezer with a Copeland semi hermetic self contained 1 hp unit on roof of the box, stuck in the hottest corner of a kitchen with no fresh air flow to speak of. Ambient temp 90+ upon arrival I checked system out, it was dead empty. I pressurized with nitrogen and found a bad leak at the high side service valve stem, it had no cap. I caped it and used the receiver service valve the system held vac nice. Original factory tag showed 80oz R12, I had a fresh tank of MP66 and a new container of AB oil in the truck, got the ok from the owner to proceed. After changing the oil and pulling another vac I proceded to add 85% of the original system charge with 401B my first mistake was I added in gas instead of liquid (thought I had a dip tube in the tank) ok, I recovered the gas and added 4.25 lbs of liquid to the high side. I started the system up all looked and sounded fine pressures 8 and 225 after 30 mins box was down to 45deg and heading down, oil level held good 1/3 + glass. Suction side line temp seemed high I had not check superheat . Stepped out for lunch got back bit later compressors sounded bad and locked up just as I returned, box never got below 45 deg. My question is if I let 4lb of gas out of the 401b , what is left in the tank, is it still good or is this tank junk. Could the reason of the failure have been not enough cooling getting back to the compressor because of an imbalance of the refrigerant blend the compressor appeared to be overheated?