If the furnace has been replaced(and I hope to God that it has) check the wiring down there. R terminal is wired to r on the t-stat. W is wired to w on the stat and so on. The only problem that you might have is if there is a c terminal on your new stat. This will have to be wired to c on the unit. If you don't have a wire going to the stat for this( only enough to wire r g w and y) then you will have to get a different type of stat that doesn't have a common terminal (c).
hope that you understand tihis because I'm not sure that I do anymore