Installed 2.5 ton R-454B Payne system. Vertical air handler in hallway closet. New disconnect box for the condenser. Installed new plywood overlay for the air handler to sit on. Built and installed new extended supply plenum. Sealed all ductwork connections with mastic / hardcast. Rebuilt primary condensation drain, added new secondary safety switch. Cleared drain with CO2 and primed trap with water Pressure tested system with nitrogen and pulled vacuum. Cleaned out return chase under the air handler. Charged AC with R-454B refrigerant. Tested heating and cooling operation. Everything is working at completion of install.