Make sure the connector labels are clearly visible. If you’re not sure what type of heating you have, contact a local pro. Diagram of conTrol wire connecTions for 7-wire mulTi-sTage heaT pump wiTh mulTi-sTage auxiliary heaT conTrol wires plus c wire O wire (or) B wire – changeover valve NOTE: If both O and B are present connect ONLY the O wire. either Rc or Rh on the Nest thermostat. This particular wire extends from the transformer and is responsible for completing the 24 V power circuit in the thermostat. A wire labeled O, B, or O/B is used to control whether a heat pump is in heating or cooling mode. Contact a local pro and have them check if your proprietary system can be rewired to be Nest compatible. Thanks delack. If you see these wires attached to your thermostat, your system is not compatible with the Nest thermostat. for your heat pump to run. Note: Do not connect any Jumper wires to the Nest thermostat. Wait at least 5 minutes to see if your system turns on ( you’ll need to wait because many systems have a built-in delay). You may have an incompatible system if you don’t see your current thermostat’s wire labels listed here. Heat pump systems use a changeover valve controlled by the O/B wire. However, on some thermostats, a wire labeled B is the common wire C. In most cases, the common wire is labeled C. The common wire doesn’t have a standard color. 04/26/2020 Run the thermostat wire from your furnace to the location where your thermostat will hang. Your Nest If not a Trane product O is typically not used. S, S1, S2: These wires run directly outside and provide outdoor temperature information to the thermostat. to help heat your home. 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. The wire in the W2 connector controls the second stage of heat. rely on color alone to determine the function of a wire. stat's terminal block and tighten the screws to secure the wires (figure 3, wiring detail B). 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 07/25/2019 If your system has a dehumidifier wire, or more than one dehumidifier wire, you need a professional installation. Some heating and cooling systems have fans with multiple speeds. Pro can determine how to install your dehumidifier. Accessibility. Henry Tuesday - Systems that are incompatible with the Nest thermostat. Note: O/B wires are typically orange, but you should not rely on O & B Terminals O and B wires control when your heat pump cools or heats your home. Auxiliary heat helps heat your home when it’s too cold outside outside Install your Nest thermostat without these wires. You’ll know that the power is off if your system doesn’t turn on. O, B, O/B: These wires are responsible for switching the changeover valve in a heat pump system. Knowing what each letter stands for and what it’s used for can help you figure out which wire goes where on your new thermostat. Here’s what those letters mean. The wire will run through a dedicated opening on the side of the furnace into the control panel. 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. However, on some thermostats, a wire labeled B is the common wire C. In most cases, the common wire is labeled C. These types of wires are not compatible with the Nest thermostat. @craiglloyd. Tuck the wires into the wall keeping them flush so the thermostat snaps in … Once you’re sure you’ve turned off the power, look for a removable panel on your system. My parents have a zoned forced air system, which means the existing thermostat has the following wires: O B G Y R W The issue is that the O and B wires, which I guess control the zone damper, cannot be separately hooked up to O and B terminals on the new programmable thermostat. 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 A wire labeled O, B, or O/B is used to control whether a heat pump is in heating or cooling mode. Your fan pushes the warm or cool air, Y3 wires indicate a system that has three stages of cooling. cold outside for your regular heater to keep your home warm. Proprietary systems usually only work with thermostats made by the same manufacturer. While the old standards (e.g. Sometimes it might be a single O/B wire instead of two separate wires. Note that the temperature sensor is not polarity sensitive. the 4-wire RGYW system), many HVACs have alternate wirings designed for more advanced thermostats. Page 22 The 2nd generation Nest Learning Thermostat will use System Match to recognize your system as a two-stage heat pump if you’ve connected Y1, Y2, and O/B wires. My old thermostat (honewell TB8575A1000U) has wires connected to R, W/X, Y/A, GL, GM, GH and C. My new thermostat does NOT have these same identifiers, (honeywell RTH2300). X, AUX: Some heat pump systems can provide auxiliary heat. The installer could have used any color, though. 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. Some thermostats have wire connectors with two sets of labels: one for conventional systems, one for systems with a heat pump. compressor is responsible for heating and cooling your home. Make sure there are no lights that might indicate your system still has power. On some systems, such as Rheem and Rudd, you'll find a B terminal that performs the same function as the O terminal. system you have. It sounds like the new thermostat is not compatible with your system. 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. You just need to connect ‘red’ wire from furnace to Rh and ‘white’ wire to W1. See the following article if you need more information about thermostat wire labels. Begin setup with the app to get a custom wiring diagram. A G2 You need to look at the zone controller. When you’ve removed the panel, look for the control board. Jumpers aren’t connected to the system and don’t run back into the wall. Use the picture of your system’s connectors to enter wires into the Nest app. The wires I have are R, C, G, Y1 and W1 only. Note: This is not a complete list of all incompatible wires since there are so many possibilities. A G3 Here are some of the wire labels you might see on your thermostat and what they do. In some installations the common wire may be disguised as a B wire. Anyone know if Red and White would at least start the furnace? If you have a heat pump, your Y or Y1 wire controls your compressor. 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. Wiring details F. After running the thermostat wire through the hole, seal to prevent air from the wall cavity from affecting the thermostat's temperature sensor. center using thermostat wire. 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. Some heating and cooling systems have fans with multiple speeds. Article by: Some HVAC systems, called dual transformer systems, use separate E: This works nearly identically to auxiliary heat, but for emergency purposes only. Before you turn off the power, make sure each wire coming to your thermostat is a different color. Double check that you turned off the power to your heating and cooling system. Your Nest pro can determine how to install your humidifier. Jumper wires connect two thermostat terminals together (often Rc and Rh), but they aren’t “two label” wires. Wires labeled L can be indicator lights. Mount O, B, O/B: These wires are responsible for switching the changeover valve in a heat pump system. Rh and an Rc wire, you have a dual transformer system. Worth a look: Occasionally, the wire labelled B may in fact be the common wire (C), which is needed to power an ecobee … It looks like a circuit board and usually has lots of wires attached to it. Your pro can tell which speed this wire controls. These 2 connections will set the Nest thermostat as a ‘smart 2 wire thermostat’ taking care of your home heating ‘smartly’. 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. and cooling. Putting wires into the wrong thermostat connectors during setup can cause your system to malfunction or possibly damage it. If you’re replacing your thermostat for the first time, you might notice that the wires are connected to different terminals, each of which is denoted by a certain letter. 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. 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