I have a original Lennox heater and condenser. They are both as old as our home which is 1976. They are both still working. The condensor has always been undersized for the house. 3 ton says 2 1/2 ton working as a 3 ton. It has been such good quality I don't know what brand to get as Lennox now is one of the most expensive. How Do i know what to replace with. Someone said American Standard 13 seer would be better than what I have. Any suggestions????