Completed one system matience on 19 year old American standard heat pump. Unit is heating properly at this time, including refrigerant levels. Unit is starting to have bacteria growths inside the system pictures attached. There is also a large amount of rodent evidence on top of and around unit. Attic is also low in insulation as well. Pictures and estimates attached. In addition to estimates I would recommend getting an exterminator out for the rodent droppings in attic. They will often chew through wires in and around your systems and cause problems/breakdowns.