Want to replace our 15+ year old air handler with a 3 ton Trane gas furnace like XB80 or XR80. But should I keep the old a/c outside? It is a Trane XL1200 (mfd date 4/93). The contractor said that it is not a good idea because the mismatch may give me problems, and it will only lower my cost by $800 (seems low to me) now but it will cost hundreds more dollar to replace it later. He wants me to go with a new unit like XB13, XR14, or XL14i.
What shall I do?