I found the "Why doesn't the “fan on” mode work after I installed a new thermostat?" thread on this site and am wondering if the manual rewire steps would also work for a two wire system. The setup: older house with Trane XV80 furnace, two wire setup, thermostat/Rh to controller board/R; thermostat/W to controller board/W1; thermostat Rc to Rh jumper; controller board W1 to W2 jumper. As I understand it an additional green wire would be the best solution, but that's not an option for me. Can I get the fan to run continuously during the summer by manually moving the thermostat wire from Rh to G and the controller board end from W1 to G? Thanks.
It's probably simpler to just wire a switch at the furnace wired R and G. In the summer you just hit the switch. You can switch the wires in your furnace and thermostat to have control at the stat. Or you could install a Fast Stat, which uses two wires to signal a full complement of wires.