HOW THE C-WIRE WORKS ON YOUR THERMOSTAT

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Known as the common wire, (C-Wire) provides Wi-Fi thermostats continuous power from heating (e.g. furnaces) and cooling systems (e.g. Air Conditioning systems). C-Wires are required on all Resideo Wi-Fi thermostats.

For full thermostat wiring assistance: Click here. To purchase a c-wire adaptor: Click Here.

How to check if your thermostat is using a C-Wire.

 

  1. Turn off power supply

    For your safety, turn off power at the breaker box or switch that powers your furnace or air conditioning.
    Note: Turning off your thermostat won't turn off the power to the furnace or heating equipment.

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  2. Verify your system is off

    Try adjusting your thermostat’s temperature setting, if you don’t feel the system running within 5 minutes, the power is off. If you have a thermostat with a digital display and it goes blank, you can skip this process.

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  3. Remove your existing thermostat

    Take thermostat off wall plate but leave wires connected.
    Tip: Most thermostats can be removed by grasping and gently pulling. Other thermostats may have screws, buttons, or clasps.

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  4. Look for a wire in the C-Terminal on the wall plate

    YES – This means your thermostat is using a C-Wire. Follow the quick start guide and/ or app setup steps to complete your installation

    NO – If you are installing a Resideo Wi-Fi thermostat, a C-Wire is required. Please view the next section to learn what to do if your thermostat is missing a C-Wire.

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If you're installing a new thermostat, but your existing one is missing a C-Wire, you have the following options:


How to check for an unused C-Wire

Some homes have an unused C-Wire hidden in the wall. These steps will require access to your HVAC system.
Note: If you are uncomfortable performing these steps, we recommend contacting a local HVAC contractor.

See steps 1,2 & 3 above

  • Turn off power supply and verify that your (heating/air conditioning) system power is off
  • Remove your thermostat from the wall
  • Keep wires connected

  1. Take a picture of your existing wall plate's wiring

    Make sure you get a good view of all terminal letters (some terminals may have additional letters above, below, or to the side). You may need to reference this image later.

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  2. Label wires

    Label each wire on your existing wall plate with the stickers provided with your new thermostat. If you don't have stickers, you can use tape and a pen. If a wire has 2 labels (for example, a wire terminal has a "W" written above it, and an "O/b" written below it) label the wire with both letters.

    Note: Don't label jumper wires that only connect between terminals.

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  3. Write down the colors of the wires

    Check the boxes and write down the color of the wires connected to terminals in the existing wall plate. Check all that apply (not all will apply).

    Note: If there are wires in terminals that aren't listed, you will need additional wiring support. Contact Support at 1-855-733-5465.

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  4. Do you have an unused wire?

    Gently pull the wires towards you. Look where the wires come out of the wire bundle sleeve or sheath (Where the little colored wires converge into one cable). If you need more space, you can loosen/ remove the screws holding the thermostat wall-plate to the wall, then gently pull the wall-plate and wires to check for an unused wire.

    YES – You can use this unused wire as a C wire to install your new thermostat (this will require connecting the unused wire to the C terminal at your thermostat, and at your HVAC equipment) – Proceed to the next step.

    NO – You may be able to use our C Wire adaptor. Please scroll to the C Wire Adapter section further below.


  5. Label and connect your unused wire

    Label your unused wire with the "C" sticker provided with your new thermostat. If you don't have stickers, you can use tape and a pen. You may need to use a wire stripper to expose at least 1/4 inch of wire.

    Note: If you have multiple unused wires, then label only one wire and make note of the color.

    C-Wire


  6. Go to your furnace or heating system

    This system is often located in your basement, attic, or utility room:

    A) Remove cover from furnace or heating system:

    Open the heating and cooling system's cover to find the control board. The control board may be at the top or the bottom. You should see the same terminal labels that are on your thermostat. (Refer to your picture)

    Note: If you don't see a control board, your system may not be compatible. Contact Support at 1-855-733-5465 to find a pro-installer.

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    B) Find the other end of the unused wire:

    Locate the other end of your thermostat wiring near your furnace or heating system, and then find the unused wire.

    Note: The unused wire should be the same color as the one near your existing thermostat. See Step 3 for the color you wrote down.

    C) Connect the unused wire to the C-terminal in the control board

    Note: If there are existing wires in the C-terminal, make sure they are still connected after connecting the unused wire.

    D) Close the cover to the furnace or heating system

    Be sure the cover is completely closed. Some systems won't power up if the cover isn't fully closed.

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    Congratulations: You've connected a C-Wire! You won't need to use a C-Wire Adapter. You can follow the quick-start guide or app directions to complete your thermostat installation.


How to use a C-Wire Adapter

A C-Wire Adapter replaces the need for a C-Wire. Review the steps below. You can purchase a C-Wire Adapter here.

To use a C-Wire Adapter, you will require access to your HVAC system.

NOTE: If at any point you are uncomfortable completing the steps, we recommend contacting a local HVAC contractor


  1. Do you have a G and Y wire?

    In the previous steps, you labeled the wires of your existing wall plate. Look at those wires by referring to your picture and make sure you have both a G and Y labeled.

    YES – This means your system is compatible with the C-Wire Adapter. Continue to the next step.

    NO – Your system is not compatible with the C-Wire Adapter. Contact Support at 1-855-733-5465 to find a pro-installer.

  2. Relabel your G-Wire to "C"

    Relabel your G-Wire with the "C" sticker provided with your new thermostat. If you don't have stickers, you can use tape and a pen.

    C-Wire

  3. Relabel your Y-Wire to "K"

    Relabel your Y-Wire with the "K" sticker provided with your new thermostat. If you don't have stickers, you can use tape and a pen.

    C-Wire

  4. Go to your furnace or heating system

    This system is often located in your basement, attic, or garage. Bring a flashlight, labels, phone, and screwdriver.

    A) Remove cover from furnace or heating system

    Open the heating and cooling system's cover to find the control board. You should see the same terminal labels that are on your thermostat.

    Note: You may need to unscrew the cover. The control board may be at the top or the bottom.

    C-Wire

    B) Take a picture of the control panel wiring

    Make sure you get a good view of the following terminals, since you may need to reference this image later:

    • G
    • C
    • R
    • W or W1 (not in all systems)
    • Y or Y1

    Note: If you have wires connected to two R-Terminals, then you have a two-transformer system and need additional assistance. Contact Support at 1-855-733-5465 to find a pro-installer.

    C-Wire

    C) Label wires

    Label each the following wires with the stickers provided with your new thermostat:

    • G
    • C
    • R
    • W or W1 (not in all systems)
    • Y or Y1

    If you don't have stickers, you can use tape and a pen.

    Note: If multiple wires are connected to a terminal, only label the wires running to your thermostat *.

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    D) Disconnect the labeled wires

    Disconnect only the wires that you labeled. Don't disconnect any unlabeled wires. If unlabeled wires disconnect, reconnect immediately.

    Note: You may need a screwdriver to release wires from terminals.

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    E) Connect labeled wires to the C-Wire Adapter

    On the C-Wire Adapter's "Thermostat" side, press down a tab to open the corresponding terminal. Insert the labeled wires to the following terminals:

    • W-Wire --> W-Terminal
    • G-Wire --> C Terminal
    • Y-Wire --> K-Terminal
    • R-Wire --> R-Terminal

    Note: This will convert G into C, and Y into K.

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    F) Make sure the wires are connected

    Gently tug on the wires to make sure they are connected to the C-Wire Adapter.

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    G) Connect C-Wire Adapter to control board

    On the C-Wire Adapter's "Equipment" side, connect the wires to the corresponding terminals on the control board.

    Note: Be sure to remove the plastic tip on each wire before connecting to a terminal.

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    H) Mount C-Wire Adapter

    Use the included mount and adhesive pad to attach the C-Wire Adapter inside your furnace or heating system.

    Note: Make sure your wires aren't over-extended or strained.

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    I) Close the cover to the furnace or heating system

    Be sure the cover is completely closed. Some systems won't power up if the cover isn't fully closed.

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    Congratulations: You’ve connected a C-Wire Adapter! You can now finish the installation of your new thermostat!

 

 

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