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Thermostat Wiring

Yep, didn't mark wires before disconnecting from old thermostat. Blue wire to B, Orange to O, and so on and so forth doesn't work...nothing happens. I saw somewhere where you should be able to figure it out by looking at the wires on the furnace but that confused me more...2 white wires, a red and yellow attached to Y, for example. Picture of wires to furnace and new thermostat posted. Please help!


  • JUGHNEJUGHNE Posts: 5,730Member
    At the furnace: the white wire on "C" and the red wire on "Y" are in a separate cable go to your outside AC unit. So the remaining wires in the cable from the furnace to T-stat you would match up at the T-stat by color and letter R_W_G_Y.
  • bpro1985bpro1985 Posts: 3Member
    Thank you! So here's a pic of how I have it set up. On the furnace R is red, Y is yellow and so on and on the T-stat I did the same thing red to R, yellow to Y on and so on. I also have a blue and orange wire and a B and O, did blue to B and orange to O. It's not working. Also attached a pic zoomed out on the furnace wires, the blue and orange wires are just wrapped around a cord. Shouldn't it be working, what is wrong?
  • mjw73mjw73 Posts: 2Member
    everything looks good with wiring..did it work before you changed t-stat??double check switches and tstat settings if yes..
  • MarzMarz Posts: 90Member
    Maybe there's a bad 3 amp fuse? Looks like a Honeywell ST9103A board. I know there are different revisions for that one. And some older ones can be problematic. Check for burn marks on the back of the board.
  • MarzMarz Posts: 90Member
    Hmm maybe not a st9103. Hard to tell.
  • JUGHNEJUGHNE Posts: 5,730Member
    As asked, did the system work before you changed T-stat?

    I'm not familiar with that T-stat, but there is probably an installer's manual included that requires you to program the T-stat for the particular type of system you have. And of course the batteries must be installed correctly.

    Make sure the blue and orange do not touch other or anything at all. (Usually if you don't need the wires you don't connect them at just one end)

    The 3 amp fuse is in the furnace near the terminal "C", it is an automotive type. The 3 looks like the letter "E".
  • bpro1985bpro1985 Posts: 3Member
    Thanks for your help everyone! The little knob that when the furnace door is off it won't run was it was stuck in the door open position.
  • BillWBillW Posts: 198Member
    Many Honeywell stats were designed for multiple uses on conventional or heat pump applications. O&B terminals are usually for changeover on a heat pump.
  • JUGHNEJUGHNE Posts: 5,730Member
    That is a furnace door safety switch whose purpose is to prevent burner operation with the door off of the blower compartment which would pull exhaust fumes, including carbon monoxide, out of the furnace and into your house.

    You should replace it if you have not already.
  • Empire_2Empire_2 Posts: 2,343Member
    Jughne,.....I was always taught it was so the cat would not take and unfortunate tumble.....? Others told me it was so 9 month old children would not get hurt, and here is the kicker,....Has. the problem been fixed? Nothing drives me more crazy when someone asks for help the abandoned the topic. Forget O and B. It's not used, at least in this set up. If the fuse is blown there is more than likely a short in the A/C contactor or the wiring leading out to the condenser. Electricity and or control voltage knows NO color! I too looked at the C.B and the stat configuration, there should be no problem, but if the consumer shorted something out, we can only speculate......

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