It seemed that all he wanted to so was to sell me a new A/C unit for $12K. He statement when he first got here was that he wanted to make sure that the system was "Safe". After a short time on the roof, he came back and said, "That it was not safe because of rust." There is rust but the unit should last another couple of years. second and third opinions. What was wrong as we found out was that the cold air return was 16" and it should had been 20" for a 5 ton unit. You installed the unit 13 years ago and should have know. So by all rights you should install a new unit for free since it was not getting the proper airflow which caused excessive condensation on the coils what caused the rust.