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I can't figure out why my furnace is not working in FAN ONLY mode. It works fine when calling for heat, but when Fan is set to ON and there is no call for heat (or heat is turned off) the fan does not respond.

The T-stat is a Honeywell Vision Pro 8000. It is set to Heat+Fan mode and wired according to the manual with R, W, and G wires (see photos). The furnace is a Goodman gas furnace. I can't find the exact model number but the attached photo shows a sticker inside the coverplate that lists a few model numbers (it must be one of those). It was installed in 2008 so I assume it's capable of running the fan only. Also attached is a photo of the T-stat wires connected to the R W and G contacts of the furnace control board. I have also verified there is continuity of the G wire at each end.

Any help is much appreciated!

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I notice that you have two red wires used for R and W.

Perhaps they have been swapped, so the wire labeled "R" at the thermostat is actually connected to "W" on the furnace control board, and vice versa. That would mean that when the thermostat tries to activate the fan, it is just connecting the wires for heat and fan, without connecting the power from R to anything, and so nothing happens.

If so, then you just need to swap back the two red wires and the fan control should work properly.

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  • I would be checking that also
    – Ed Beal
    Commented Dec 31, 2020 at 14:48
  • Indeed! That was the culprit. I swapped the red wires and we’re in business now! Thanks so much for the help!
    – dlamar
    Commented Jan 1, 2021 at 22:32

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