I'm about to replace my old condenser unit and I want to know what else I really have to get to match it. it's a 13 year old Trane XB1000 10 SEER 4 ton unit that has had a hard life. My air handler/evaporator (enclosed, on top of the furnace unit), is pretty corroded looking, so I guess I need to replace that also, and the big fan that is bolted to the bottom of the gas furnace area is pretty old also, with corrosion on the blades. But the furnace itself works fine, and the ducts have just been redone from the air handler and in the attic, so I just want to replace the evap unit, outside unit and the big fan on bottom without disturbing the furnace or other parts. Also, my house is only 1400 square feet, and I live in a pretty dry climate, so I'm thinking I really should have no more than a 3 ton unit. And I should probably update to the new coolant type. So, can I replace those parts with 3 ton parts and keep all the old coolant hoses, furnace, etc? By the way, I'm hiring someone to do the work, I just want to buy the parts first.