What all those letters mean when it comes to your thermostat's wiring.
This post was published in June of 2019.Because more people are searching for this kind of fix right now, we are republishing it as part of a home focused week at iFixit.
If you are replacing your thermostat for the first time, you might notice that the wires are connected to different terminals, each of which is a letter.The letters mean something.
It is easy to replace a thermostat, but sometimes the terminal letters on the old thermostat don't match the ones on your new thermostat.It is possible to figure out which wire goes where on your new thermostat by knowing what each letter stands for.
It is a good idea to shut the power off to your entire heating and cooling system before you replace the thermostat as it will not cause any issues with the electrical system.
A single Rh or Rc wire may be all your system has.If you only have an R wire, it is your responsibility to power your entire system.If you have both an Rh and an Rc wire, the former powers the heating and the latter the cooling.The R wire is the one that controls the heating system.
The blower fan pushes the warm or cool air through the vents in your house.It isn't a ground wire.
The power to the thermostat is provided by the common wire.If your system has a terminal for it on your thermostat, you should connect it since some systems don't provide this, and some can be powered by a battery or just "steal" power from other wires.
The Y wire is used to send a signal to your air conditioning system when your thermostat calls for cooling.If you have a two-stage system, Y1 and Y2 wires might be used instead.A high and low level for extremely hot or cold days.
The wires are used to switch the changeover valve in a heat pump system.The O and B wires switch the valve from cooling to heating.It could be a single O/B wire.
auxiliary heat can be provided by some heat pump systems.If the outside temperature is too cold for the heat pump to work alone, this wire will send a signal to your system.The air handler has a secondary heat source.
This works similarly to heat, but only for emergency purposes.If need be, auxiliary heat can be turned on automatically.If you have a heat pump problem, emergency heat is only used.
This terminal is used to connect equipment like a whole-house humidifier.
When auxiliary or emergency heat is turned on, or if there is a general problem with your system, this terminal is designated for indicator lights on the thermostat.
The Y and G wires are combined to form a single K wire that connects to the K terminal on some thermostats.It is used for systems that do not provide a C wire but have a thermostat.
The wires run directly outside and give the outdoor temperature information to the thermostat.
This is a lot of information, but you can use it as a guide whenever you need to replace a thermostat.If you don't know which wire goes where, or what configurations your heating, ventilating, and air conditioning system supports, consult your manual for wiring diagram information.
You need to read the manual for your heating and cooling system and look at where the wires connect on the board.
The old standards were used.alternate wirings are designed for more advanced thermostats.
The colors can be wired to "ABCD" terminals that provide a data interface to Carrier's own thermostats, as well as the old standards for third-party thermostats.
Your article did not mention the two terminals on my thermostat.A red wire is connected to one of the labeled "HUM" and the other "DHUM".Is it a Humidifier?
Thank you delack.There is a marked H in mine.I can't get it to work because it has terminals that are G, P C, H, V.I assumed the P was rubbed off R and V.It will not start.I wonder if I could use the H terminal to run a wire to the furnace.Is Red and White going to start the furnace?
I have four wires in my thermostat and one of them went into rc and the other into g y w.There is no rh to connect with the rc on my new honey well thermostat, but there is an r terminal on the old one.Does this mean the thermostat won't work?Is it possible to connect the rh wire to the rc by putting it into the r?
My old thermostat has wires that connect to R, W/X, Y/A, GL, GM, and C.I don't know if the new thermostat is compatible with my current system.