enter image description hereI need help with wiring up the new thermostat. I have a Gas furnace heat with heat pump. Goodman Units. The old thermostat G=GREEN C=BLUE Y=YELLOW R=RED O=ORANGE b=BLACK E=WHITE. The new thermostat has g,c,y.e,r but O/B is one terminal so Im unsure how to finish up. The other options are w2/aux, k l/a,s,s u See image of new thermostat setup. So does the Orange wire go to o/b and the black wire??

Here are the pictures you requested. Appears black wire not used??

enter image description here enter image description here enter image description here

Thanks for all the help!!

Here is the final setup that I went with. Forgot to take picture so just used graphic on new setup.

enter image description here

  • Can you post photos of the thermostat wiring at the furnace end? Jan 23, 2020 at 4:14
  • I will get those pictures this evening. Thanks for responding. Jan 23, 2020 at 12:58
  • @TimothyJennings Welcome to the site! Please register and merge your accounts so you have access to edit, comment, and accept answers on your own question. Note that posting responses as answers can result in an automated lock that can prevent others from assisting you.
    – BMitch
    Jan 23, 2020 at 14:18
  • The O is commonly used for the changeover valve in the heatpump, and B (black, brown) can be used for aux/emergency heat or also changeover valves. That's why the other end of the wiring is important. Either that or the original manual for the old thermostat.
    – JPhi1618
    Jan 23, 2020 at 16:55

1 Answer 1


This isn't so hard after all

Old bimetal thermostats used extra contacts on the mode select (heat/off/cool/e-heat) switch to determine whether O or B was energized, so as a result, your old thermostat provided both an O and a B terminal, in order to be compatible with all heat pump systems, as some require an O wire while others require a B wire. However, there are very few systems (certain residential zone boards are the only setups I know of) that require both O and B to be present; all heat pumps and many other systems that use O/B require only one or the other.

In your case, your O wire is connected to your heat pump reversing valve (the orange wire in the thermostat cable is connected to the orange wire going off to the heat pump), while the black wire in the thermostat cable is unconnected at the furnace end of the system, apparently. As a result, the orange wire goes to the O/B terminal in your new thermostat, while the black wire can safely be left unhooked, since it goes nowhere anyway. Also, the white wire that was connected to E on the old thermostat needs to go to AUX on your new thermostat, due to the way it handles auxiliary/emergency heat. The rest of the wires go to the obvious terminals: red to R, blue to C, yellow to Y/Y1, and green to G.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.