I have a gas fired furnace in the pole barn of a house I just bought. The thermostat has a two wire lead running to it, with connections to "W" and "R". It functions properly in the heat/auto mode, but will not work in the fan only mode. Any idea how to make it work in fan only mode? Based on looking at the house thermostat, I'm guessing that I need another two wire lead to "G" and "Y" ---anyone know for sure.