Changing a furnace "common" or "fan" wire - how to?

Post date: 2021-06-19 03:01:19
Views: 72
I had a new furnace installed and the installer changed the wiring to the thermostat in an unhelpful way. The green wire, which used to be "fan," is now "common." I don't really want that. Is there an easy fix?

I should probably just call the company and have them come out and change it, but there is a hassle factor because we would need to be home at the right time, etc.

What happened is this: I have a Nest thermostat and we like to use the "fan only" function to circulate air in the house all day -- i.e., 15 or 30 min an hour. With the old setup, I used the green wire from the furnace and plugged it into the "G" port on the Nest, which allowed it to run the fan. We did not have a "C" wire (common), but this was not a problem because the Nest could charge when the fan was running.

The new furnace guy changed the green wire to a "common wire," which has much higher voltage than the old "fan" wire. He plugged the green wire into the "C" port on the Nest rather than the "G" port. Now I no longer have the "fan only" option because the Nest no longer has a "G" wire to operate the fan. He did this so my Nest could charge through the common wire, but I didn't really need that because of the way we use the fan.

I stupidly tried plugging the green wire into the G port, but blew a fuse in the furnace, which I replaced. I put the wire back into C and it is working fine, except no fan control.

Is this hard to switch over so I have a "fan" wire rather than a "common" wire on the green wire? Or should I just call the guy?
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