Installed 4 ton Carrier heat pump system. Built and installed new supply plenum. Installed new plywood overlay for new air handler to sit on. Sealed all ductwork connections with mastic/hardcast. Cleaned out the return chase underneath the air handler. Rebuilt primary condensation drain, added safety switch to secondary. Cleared primary drain with CO2 and primed trap with water. Pressure tested system with nitrogen and pulled vacuum. Charge AC with R-454B refrigerant. Tested heating and cooling operation of new system. Everything is working at completion of install.