I am installing a Lux TX9000TS digital thermostat. The wires I have are Red, White, Blue & Green. On the Thermostat I have W, Y, G, B, O, RH RC (Jumper) & C. My question is where does the Blue wire go? My father in law put it on the B, but when the furnace kicks on, the AC fan also kicks on. I have a Bryant Plus 90 Gas Furnace and an old Central AC unit (don't know the name). From what I've read, the Blue is either going to go to C or Y, but which one is it? Thanks!