For this super tune-up I inspected the customers upstairs and downstairs air handler and condensers. The downstairs system is from 1990 and covered in biological growth on the blower wheel and throughout the plenum and ductwork. The secondary drain pan is rusted as well which could lead to twarer leaking into the ceiling if the water backs up into the system. I only had a 7⁰ difference from return to supply because there is a leak in the evaporator coil. With the system being 35 years old my ultimate suggestion would be complete system replacement as any repairs would just be bandaiding the problem. I spoke to the customers about what I found and they would like to speak to a CA Monday between 3-5 about replacement.