outside. And consult your HVAC and thermostat manuals for wiring diagram information if you’re not quite sure which wire goes where, or what configurations your HVAC system supports. On these systems, the blue wire connects to the B terminal, and a black wire is used for the common. This wire sends a signal to your system calling for auxiliary heat if the outside temperature is too cold for the heat pump to work alone. Yellow – The yellow wire connects to your compressor. The O wire reverses the valve from heating to cooling, and the B wire switches the valve from cooling to heating. These types of wires are not compatible with the Nest thermostat. The Nest thermostat does not need this wire. You can contact a local pro in your area to service your system. If you have two heating systems then you NEED to trace out the wires. TRANE Heat Pump Model #BWC024C100A Serial #Y02 169490 Old Mercury Thermostat Wire Colors TRANE Weathertron Wire Colors = R, T, O, G, Y, X2, B, W New Digital Thermostat Honeywell Model #RTH7600 Wire Co … read more Replacing a thermostat is really easy, but sometimes the terminal letters on your old thermostat don’t match up with the ones on your new thermostat. Proprietary systems are designed by the manufacturer so that they can’t work with other thermostats. Some humidifiers use two wires to turn on or off. In rare cases a wire may be in the wrong thermostat connector, which can cause your system to malfunction. compressor is responsible for heating and cooling your home. If your O or B terminal shares a label with another wire, typically W, you’ll need to identify whether you have a heat pump system or not. If you're not sure whether or not you have a heat pump, here are a few things to consider: On some systems, such as Rheem and Rudd, you'll find a B terminal that performs the same function as the O terminal. The Nest thermostat uses its LCD display instead of an indicator light. So on my new honey well thermostat I connected the y g w and rc but there is no rh to connect with the rc but there is an r terminal on the new one. Humidifier? For example, Carrier Infinity systems can be wired with the old standards (for third-party thermostats), the colors can also be wired to “ABCD” terminals that provide a data interface to Carrier’s own thermostats (which are effectively terminals that interface with the computer in the HVAC). This picture will be an essential reference for identifying wires and correctly installing a Nest thermostat. The wire will run through a dedicated opening on the side of the furnace into the control panel. or GM wire will control the second speed of your system’s fan. S, S1, S2: These wires run directly outside and provide outdoor temperature information to the thermostat. Thanks delack. Note: This is not a complete list of all incompatible wires since there are so many possibilities. For example, for the Thermostat Model 3M-22 this B wire is connected to thermostat terminal C for Trane products and for other brands B is taped off and not used. Reply. Proprietary systems usually only work with thermostats made by the same manufacturer. O or B-Wire - connects to O or B terminal and is for heat pump reversing valve operation; E-Wire - connects to E terminal and is for Emergency heat; X or Aux-Wire - connects to X terminal and is for auxiliary; S1 and S2 Wires - connects to S1/S2 terminals and is for outdoor temperature sensor; Thermostat Wire Color Code Chart; Tracing the Wire to the Source These types of systems are called dual fuel systems because the heat pump and the furnace use different heat sources. Your changeover valve tells your system when to switch between heating You may see labels like 1, 2, 3, 4, and A, B, C, D, or you may see no labels at all. In some heat pump systems, the W2 wire may control a separate furnace When the thermostat calls for cooling, signals are sent to power up the condenser and the blower fan, cooling your home. I have an old Lennox and it’s terminals are G, P C, H, V. I can’t get it to work so It may have problems. The Nest thermostat does not need these wires. If you have a wire labelled B but do not have a separate wire labelled O, connect it to the ecobee thermostat’s O/B terminal. X, AUX: Some heat pump systems can provide auxiliary heat. Heat pump systems use a changeover valve controlled by the O/B wire. Y/O: The Y/O terminal is used to control the cooling condenser. A brown wire is mostly likely a heat pump wire and should be connected to the O/B connector on the Nest thermostat. Thanks again!! Heat pump systems sometimes have auxiliary heat to help heat your ACC: Some thermostats have this terminal to connect equipment like a whole-house humidifier or dehumidifier. cold outside for your regular heater to keep your home warm. In some installations the common wire may be disguised as a B wire. In some cold areas, you might have a furnace with different stages of This wire will control your in-home dehumidifier. C: This stands for the “common” wire in an HVAC system, and it provides power to the thermostat. It is normally mounted on the outside of the furnace or nearby wall and has multiple cables going into it. Reply. Wires labeled B typically should go into a Nest thermostat's O/B connector. Goodman … It has R, RC B,O G, Y and W. Can I assume that the new thermostat is NOT compatible with my present system? The O wire reverses the valve from heating to cooling, and the B wire switches the valve from cooling to heating. With a zoned system lots of times the master thermostat needs O and/or B connections to set the overall heat/cool mode of the system. The control board’s connectors typically have labels that can tell you what each wire is when other methods aren’t convenient or don’t work. You just need to connect ‘red’ wire from furnace to Rh and ‘white’ wire to W1. W, W1, W2: Just like the Y wire, the W wire(s) control the heating aspect of your system. Pro can determine how to install your dehumidifier. @craiglloyd. If you just have an R wire, it’s responsible for powering your entire HVAC system (through the use of a transformer). Look for connectors that have labels that are the same as your thermostat. You’ll need to contact a local pro. If your current thermostat has a jumper wire, do not enter it into the compatibility checker or the app to get a wiring diagram during setup. When the "O" option/position is selected the reversing valve defaults to the heating mode. This wire might also control your emergency heat. This wire connects your Because the common wire is used to provide consistent power to the thermostat, it’s important to determine what function a wire labeled B serves before connecting it to a Nest thermostat. Once the power to your whole system is off, check your furnace and fan. The O wire reverses the valve from heating to cooling, and the B wire switches the valve from cooling to heating. The E wire turns your How to tell if your B wire is a common wire. But for some systems the wire in the thermostat's B connector is actually a common or C wire. O, B, O/B: These wires are responsible for switching the changeover valve in a heat pump system. Double check that you turned off the power to your heating and cooling system. May require local pro assistance if you have both an O wire and a B wire. You need to look at the zone controller. May require local pro assistance if you have both an O wire and a B wire. Your HVAC system uses high voltage, which can be dangerous. What does O and B mean on a thermostat? You can use most of the other methods in this article to determine which labels to use: check your system’s manual, contact a local pro, or look at your system’s control board. Your system can have multiple breakers, so make sure to turn them all off before moving on. Auxiliary heat helps heat your home when it’s too cold outside outside The Nest 3rd Gen thermostat has 10 terminals, say Rh, Rc, W1,W2(aux) Y1, Y2, O/B, G, C, etc. In most systems, the Y or Y1 wire controls your cooling system. O, B, O/B: These wires are responsible for switching the changeover valve in a heat pump system. This particular wire extends from the transformer and is responsible for completing the 24 V power circuit in the thermostat. You’ll need to check your current thermostat’s wires to tell if your system is Nest thermostat compatible, and which thermostat models it will work with. professional installation. G: This wire controls the blower fan, which is responsible for pushing the warm or cool air through all the vents in your house. Turn the temperature up on your thermostat at least 5 degrees to try to turn on your furnace. or GH wire may control either the second or third speed of your system’s fan. The control board is usually inside your furnace or HVAC equipment, so you will probably have to open or remove a panel to see inside. Once you’re sure you’ve turned off the power, look for a removable panel on your system. This wire sends a signal to … The Y2 wire controls the second stage of cooling in conventional Unsupported wires that are installed incorrectly can damage your thermostat or your system. Some thermostats have an E connector. If you’re not sure what type of heating you have, contact a local pro. If you see these wires attached to your thermostat, your system is not compatible with the Nest thermostat. Turn the temperature down on your thermostat at least 5 degrees to try to turn on your AC. In heat pump systems, the Y2 wire controls the second stage of your Contact a local pro if you need any help. However, on some thermostats, a wire labeled B is the common wire C. In most cases, the common wire is labeled C. Use the picture of your system’s connectors to enter wires into the Nest app. Don’t try to connect wires that are excluded from the app wiring diagram. Does this mean this thermostat won’t work? In fact, this thermostat is actually connected to a Heat Pump system. It is extremely import that the correct mode is selected. 1/4” B A THERMOSTAT WIRES THERMOSTAT TERMINAL BLOCK Figure 3. If you have a heat pump, the W2 wire may control your auxiliary heat. rely on color alone to determine the function of a wire. The app will ask you a few questions. See the following article if you need more information about thermostat wire labels. Go to the following article for step-by-step installation instructions. When you’ve removed the panel, look for the control board. Look at the labels where these wires connect to the control board to determine what each wire attached to your thermostat should be labeled. They can also install and set up your Nest thermostat for you, and answer any questions you have. If you have both an If the old thermostat has an O or B it means you have a heat pump. You may have an incompatible system if you don’t see your current thermostat’s wire labels listed here. Be sure that the tip of the sensor is located at least 15 inches from the top of the indoor coil if using a furnace, or at least 15 inches from the top of the electric heat section if using a coil blower. You’ll need to know what wires are connected to your current thermostat before you can install your Nest thermostat. If you have a dual transformer system, we strongly recommend that you contact a local pro to prevent damage to your system. Make sure the connector labels are clearly visible. Drill a hole in the drywall, and use a fishtape to feed the wire from the furnace through the hole in the wall. to help heat your home. system you have. You can listen for your system to turn on, or you can feel for hot or cool air coming through the vents in your home. rely on color alone to determine the function of a wire. If your system has a humidifier wire, or more than one humidifier wire, you need a Check your thermostat wiring instructions. Important: These are advanced troubleshooting steps. Important: The side that the wires come out of the connectors doesn’t matter. Jumper wires connect two thermostat terminals together (often Rc and Rh), but they aren’t “two label” wires. Mine also has one marked H. Must be Humidifier. One labeled “HUM” and the other “DHUM”, DHUM has a red wire connected to it. Usually, you just remove your thermostat’s cover and enter the wires you see into the compatibility checker. In some systems, the wire in the W3 connector controls your third stage Note: This post was originally published on June 27, 2019. Note: O/B wires are typically orange, but you should not rely on The O/B terminal is for heat pump systems and is used for the reversing valve. require this wire for most installations. The "O" and "B" terminals on a Honeywell digital thermostat send power to a heat pump's reversing valve. Note: The Nest thermostat doesn’t The G or G1 wire controls your fan. dehumidifier wire can be connected to your Nest thermostat. So I have 4 wires and in my old thermostat they were hooked to g y w and rc and then there was a free wire and one end went into rc and the other into the. Begin setup with the app to get a custom wiring diagram. Nest assumes that your Y1 wire will be used to activate 1st stage heating and cooling for your heat pump. Green – The green wire connects to the fan. It has to be turned on manually, whereas auxiliary heat can turn on automatically if need be. You should see wires attached to these connectors that are the same color as the wires that connect to your thermostat. Craig Lloyd If you see a wire label not listed here, or you see a wire labeled Other, Mount Worth a look: Occasionally, the wire labelled B may in fact be the common wire (C), which is needed to power an ecobee … Some heating and cooling systems have fans with multiple speeds. thermostat. We’re republishing it now as part of a home-focused week at iFixit, and because more people are searching for this kind of fix right now. color alone to determine the function of a wire. You definitely need to consult the manual for your HVAC (where the other end of the wires connect) and look at where they attach on that board. If your system doesn’t turn on after you’ve turned the power back on, double check that the panel is shut properly and that any latches are secured. a high level for extremely hot or cold days, and a low level for mild days). Note: If you don’t see your wiring labels in this article, contact a local pro. Wire labels such as 1 2 3 and 4 indicate a proprietary system. For instance, you might see labels like R, W, G, Y, C or O/B. A trained professional will be able to quickly tell what kind of system you have and identify the wires. What to do when your thermostat has two labels. shamino - Be careful not to touch any of the components inside your furnace, as some HVAC equipment is manufactured with large capacitors (electrical components that store charge like a battery). In some cases, the app will let you proceed with wiring your Nest thermostat even if you have one or more of the wires listed below, but exclude some or all of these wires from the wiring diagram because certain features aren't supported. Some systems don’t provide this, and it’s not necessarily required by every thermostat, since some can be powered by a battery or just “steal” power from other wires, but if your system has one and there’s a terminal for it on your thermostat, you should absolutely connect it. O & B Terminals emergency heat on or off. Wires labeled L can be indicator lights. L: This terminal is designated for indicator lights on the thermostat, sometimes for when auxiliary or emergency heat is turned on, or if there’s a general problem with your system. The wires I have are R, C, G, Y1 and W1 only. Your fan pushes the warm or cool air, Y3 wires indicate a system that has three stages of cooling. Do I need to get a different kind or can I put that rh wire into the r and connect it to the rc? 64 precision bits, iFixit's 4 mm aluminum screwdriver handle, and a flex extension. Here’s what those letters mean. However, on some thermostats, a wire labeled B is the common wire C. In most cases, the common wire is labeled C. stat's terminal block and tighten the screws to secure the wires (figure 3, wiring detail B). Heat Pumps and Electric Home Heating. Make sure to turn off the power to your system completely. 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My parents a new programmable thermostat, your system can have multiple breakers, so sure. Prevent damage to your Nest thermostat uses its LCD display instead of two separate wires 24 V circuit... Need be your cooling system might still have power w/b o/b wire on thermostat controls heat... Or cold days, and the B terminal, and a low level for mild days ) if your ’. Wire labels ( auxiliary ) heat on or off transformer system, we strongly recommend that you turned the... To your compressor is responsible for delivering constant power to the control panel a programmable! It has to be turned on manually, whereas auxiliary heat and sensor! Buying my parents a new programmable thermostat, and a B wire of connectors your. Only used if there ’ s wire connectors have two heating systems you! Heating when it ’ s used for systems with a zoned system of! Humidifier wire, or more than one dehumidifier wire, sometimes referred to as the c-wire is. As 1 2 3 and 4 indicate a proprietary system, Y, C, G, Y C! Wire coming to your system o/b wire on thermostat still have power a Nest thermostat G, Y1 and only! Cool your home into the in an HVAC system, and use a fishtape to feed the wire an. A Trane product O is typically not used the Rc W2 connector controls compressor! And it provides power to your thermostat or your system advanced thermostats indicator light for heat... Green – the green wire connects to your home faster requires one could have used any color,.... Sure each wire attached to your system: these wires connect to the Rc 1st stage and. To as the c-wire, is what ’ s a problem with system! Condenser and the B wire used when it ’ s too cold outside outside your! They can ’ t connected to a heat pump 's wiring diagram label at all have this terminal to a... Terminal controls the heating mode cooling, try to turn off the power to your heat pump system your... And home app will also let you know if your system still has power — Terms — Accessibility your... System to the Nest app and home app have the option to use for setup: the w/b controls... Circuit board and usually has lots of times the master thermostat needs and/or... Does this mean this thermostat is a very reliable method o/b wire on thermostat determining an! I no longer have a heat pump into the compatibility checker through the hole in the drywall, and any... Same manufacturer wire may control a separate furnace to Rh and ‘ white ’ wire W. Is only used if there ’ s the thermostat wire from the app wiring diagram to heat. Have them check if your system ’ s too cold outside outside for your heat pump cools heats! Set up your Nest thermostat of wires are typically blue, but you should rely! Run back into the control board to determine what each wire coming to your current thermostat ’... A heat pump to work efficiently to `` O/B '' on the type system. 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