I would like to have the fan turn on and blow non-a/c. I only see 2 wires coming from the thermostat. In
Trane VX99 furnace fan to run
blowerfurnacethermostat
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I would make the assumption that the furnace and fan wires are "bonded" together somewhere between your thermostat and your control board, therefore sending 24vAC to both relays and turning both on.
I'm assuming you don't have AC since you don't mention it, so in this circumstance you're probably looking at needing four wires -- ground (C), fan on, furnace on, and a positive feeder (R) (to power the thermostat and to send back to the relays).
To make the house more future-proof, I'd run more wires than needed in the event AC is ever added or the system changes configuration.
I have casual knowledge of HVAC, but in my experience of designing microcontroller-based thermostats, this is generally a good idea.
I believe you need to move the red wire at the Nest to the Rh terminal. Rh is 24v from the Heating system. The Rc terminal is 24 volts from the Cooling system. Change that around and see if your issue is fixed.
Best Answer
You have a simple setup with R (24V power) and W1 (HEAT). The fan is turned on automatically, along with HEAT, when the thermostat applies the power from R to the W1 connection.
The FAN terminal is labelled G and you need to connect that to the G terminal on your thermostat. Then, provided you have a FAN ONLY setting on your thermostat, it can control the fan independently.
You're going to have to run a "G" wire though since the currently line appears to only have 2 wires.