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I have a Trane XV90 and XL 14i. The wiring looks a little strange as in the picture bellow.

                  _____________
                  |           | 

BK W2  W1   R  G  Y  B/C  YLO O 
   |___||   |__|  ||   | 
        |   |     ||   |_____>|----------|
        |   |     ||_________>|other wire|
        |   |     |           ------------
        V   V     V
    ---------------
    |thermostat   |
    ---------------

The R and G are jumpered together and the G wire is connected on the board but is actually not connecting to the thermostat on the other end. So people told me that means the furnace fan is always on! (In my diagram above, I switched the location of Y and B/C to make diagram easier to draw. You can refer to the photo added below to see the details)

My questions are the following

  • is the jumper between O and Y doing anything? I don't think I have heat pump
  • I need to install Honeywell wifi thermostat and I am thinking of doing either one of the following:
  1. remove jumper between R and G, and use G to connect B/C and then to thermostat C and put jumper between G and Y

  2. leave jumper between R and G, and use G to connect B/C and then to thermostat C and put jumper between G and Y

  3. remove jumper between R and G, connect G on control board to thermostat G, and finally have the spare wire to connect B/C and then thermostat C

  4. leave jumper between R and G, does not connect G to thermostat, and just use a spare wire to connect B/C on board to thermostat C

Can anyone comment on those plans? Thanks a lot!

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  • First find out what you have! Don’t start disconnecting things you don’t understand. Do you need a Honeywell? Is asking if you need a ford or some other brand of thermostat. Changing your fan and cooling wiring can really mess things up. Is your furnace on or in fan on mode the thermostat may have it commanded on depending on the controls for your specific system. – Ed Beal Aug 13 at 22:11
  • Thanks Ed. I just got a Honeywell 8500 in box and want to use it. So I guess the way of tying might be just use a spare wire to connect to B/C on board and C on thermostat, without connecting G to thermostat. Just like the option 4 I just added? Thanks. – DpD_ Aug 13 at 22:34
  • This actually helps I would integrate this info into your other question and delete this one I think you will get more assistance that way. The new stat probably will have a switch to jumper r to c built in so I would remove that and check functionality. – Ed Beal Aug 13 at 22:43
  • How many wires do you have in your existing thermostat cable? Can you post a wiring diagram for your furnace/air-handler, or a link to the manual for that matter? – ThreePhaseEel Aug 13 at 22:56
  • 1
    @ThreePhaseEel I searched online and it seems the Y O jumper is used to 'activate' Trane's comfort-r feature. I don't know what exactly this feature is about but it seems to help to control the humidity level inside the house by controlling the fan speed. So you are right on this! – DpD_ Aug 19 at 3:30

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