With performed a nitrogen pressure test for circuit number 1 for the unit that serves the back right side of the store. The unit was flat out of refrigerant, we pumped it up to 360 psi of nitrogen. The machine lost 20 psi of pressure in just under 10 minutes, we sprayed all the U-Benz on the evaporator coil and the condenser and could not find any leaks. We repressurized the machine to 400 PSI, remove the top from the unit and climb inside and checked all of the connections. Sheen has lost another 50 psi in pressure however we cannot locate the leak. My suggestion would be to recover the refrigerant from circuit number 2, cut and isolate the evaporator coil and the condenser coil and pressurized each one separately. The leak must be embedded in the coil which is why we cannot find it, we can then determine which coil has failed based off of what is losing pressure.