Recovered refrigerant from old Walk-In Cooler unit and replaced condensing unit and indoor evaporator unit. Replaced drain line union. Charged unit with 300psi of nitrogen and let stand for 30 minutes with no psi drop, Used vacuum pump and pull system into a vacuum of 500 microns and let stand with no increase. Charged system with 404a refrigerant to factory specifications and waited for unit to come down in temp and satisfy.