Completed A-coil replacement on Rheem 3-ton system. Old coil showed significant formicary corrosion causing 2.5-pound R410A leak. Recovered refrigerant, replaced TXV during installation. Vacuum pulled to 200 microns, leak checked at 175 psig nitrogen. Recharged system to 12°F subcooling. Delta-T now measuring perfect 19°F across coil.