1

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.

  • There's probably a better way to set this up -- do you just want a switch somewhere you can turn the fan on during the summer with, or do you want the fan to run whenever there isn't a call for heat? – ThreePhaseEel Apr 11 at 23:23
  • Well... Good questions. I run my fan 24/7 but I'm asking regarding the mother-in-law's house, so I'm looking for the best easy/option solution. As such, an on/off switch sounds good and offers both. Fan running whenever there isn't a call for heat? I think I like the other option better. – mikep Apr 13 at 17:10
1

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.

  • Thanks for the response Joe. If I understand the first option correctly, you propose switching/changing only the controller board connection - in effect, this sounds like we're redirecting a call for heat from the thermostat to activate the fan. Is that correct? And option two allows for the thermostat fan on/auto switch to function as intended. Correct? And I see that the Fast Stat allows multiple signals over the same wire. That's pretty cool. – mikep Apr 13 at 17:11
  • I moved the red controller wire from the red terminal to the green terminal. No fan. Just a slow blinking red light indicating no call for heat.Tried resetting the thermostat through the reset button as well as taking out the batteries. Thermostat set to heat, fan to on/auto (didn't matter which) and set the temperature to hold at 20 degrees above the current temperature being displayed. Any thoughts? Thanks. – mikep Apr 28 at 23:14
  • Since the previous change had no impact, this weekend I moved the thermostat/Rh wire to G (controller board red wire still on green terminal) . Still no fan. Just a slow blinking light on the controller board. Befuddled. – mikep May 6 at 16:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.