DCM3 service 2 of 2 AC completed changed (2) aprilair 501 (1) 14x20x1 filters, tested system operation’s.upstairs system is critically low on 410A refrigerant, system should not leak refrigerant adding refrigerant will only provide temporary comfort. Upstairs AC, and furnace is from 2002 and is 22 years old Evap is from 2010 and is 14 years old. Did complementary leak search found evaporator coil extremely rusted was getting multiple hits in evaporator. Average system lifespan is 10-15 years due to age and condition would recommend replacement. Main floor and basement system are operating properly at this time. Confirmed Friday 1-2 for comfort specialist.