About Wiring Color

There is no official industry standard for wiring colors. However, the majority of manufacturers follow the common practices for installation. The following information is strictly for reference. Please be advised that the technician who did the previous installation of the thermostat may not incorporate conventional color coding for various reasons.

 Red for the R terminal. The R terminal is the power. This comes from the transformer usually located in the air handler for split systems but you may find the transformer in the condensing unit. For this reason, we advise turning off the power before adjusting the thermostat's wiring.

 Red for the RH terminal. RH – The RH terminal is designated for the power for heating when two transformers are used. See RC below for an explanation for the cooling. It should be noted that a jumper can be installed between RC and RH for a heating and cooling system equipped with a single transformer. It should be noted that a jumper wire can be installed between RC and RH for a heating and cooling system equipped with a single transformer.

 Red for the RC terminal. The RC terminal is designated to the cooling power source. Some HVAC systems consist of two transformers, one for cooling and the other for heating. In this case the power from the transformer in the air conditioning system would go to the thermostat terminal RC. It should be noted that a jumper wire can be installed between RC and RH for a heating and cooling system equipped with a single transformer.

 Yellow for the Y terminal. The Y terminal is for cooling or air conditioning and goes to the compressor relay. Typically a thermostat wire pull is made to the air handler on split systems and then this wire is spliced for the separate wire pull which is made to the condenser. Some manufacturers put a terminal board strip near the control board in the air handler so a splice is not needed.

 Yellow for the Y2 terminal. The Y2 terminal is for the second stage in cooling if your system comes so equipped. Many systems only have a single compressor, but if you have two compressors which only operate off one thermostat then you need the Y2 thermostat terminal for second-stage cooling.

Some new compressors come with two stages (two power levels), which provides wire terminals for stages Y1 and Y2.

The most common color used for this terminal and wire designation is light blue, but this varies according to the installer's preference.

 White for the W terminal. The W terminal is for heating. This wire should connect directly to the heating source whether it be for a furnace (gas, oil, electric), boiler, or heat pump auxiliary heating.

 White for the W2 terminal. The W2 terminal is used for second-stage heating. There are low and high fire gasses with some depending on control from a two-stage heating thermostat with a W2 terminal.

Heat pumps include staging for auxiliary heat and need a W2 terminal.

The most common color for this terminal and wire designation is brown, but this varies according to the installer's preference.

 Green for the W terminal. The G terminal is used for the fan relay to energize the indoor fan. On a split system the fan is in the air handler, while with a package unit the fan is outdoors.

You may notice that some G terminals on the terminal's furnace block are connected with separate wires for heating and cooling split systems.

 C stands for common. The C terminal originated from the transformer and is necessary to complete the 24-volt power circuit in the thermostat, but only if the thermostat consumes a high volume of electricity like the Vine Wi-Fi thermostat.

There is no universal color inherent to this terminal although black is most commonly used.

 O stands for orange and B for dark blue. The O and B terminals are for heat pumps; the B terminal is used in conjunction with Rheem, Ruud, or any other manufacturer that energizes the reversing valve in the heat pump's heating mode.

Most other manufacturers of heat pumps will utilize the reversing valve for cooling including the O thermostat. This wire connects to the outside heat pump condenser where the reversing valve is located.

If you have any other manufacturer other than Rheem or Ruud you will be utilizing the orange O wire for the reversing valve; Rheem and Ruud usually utilize the blue B wire for the reversing valve.

 Aux stands for auxiliary heating. The X terminal is used as a heat pump's backup and allows for auxiliary heating from the backup heating source usually located in the air handler.

There is no universal color inherent to this terminal designation, but it should be wired directly to the heating relay or Aux terminal in the air handler's or package unit's terminal strip board if you have a heat pump package unit.

 E stands for Emergency heating. The E terminal is for heat pumps and stands for Emergency Heating. If for whatever reason the heat pump condenser fails and it is necessary to run the heat there is an option on heat pump thermostats for emergency heating. This simply utilizes the backup heating source most heat pumps have to heat the home without sending a signal to the condenser to run the heat.

There is no universal color inherent to this terminal designation, but it should be wired directly to the heating relay or E terminal on the air handler's or package unit's terminal block if you have a heat pump package unit.