Old Trane Thermostat Wiring To New Thermostat [Full Guide]

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If you’re replacing an old Trane thermostat with a new thermostat, it’s important to follow the proper wiring instructions to ensure that your HVAC system functions correctly. However, navigating the wiring can be challenging, as different thermostats may have different wiring configurations.

 In this guide, we’ll guide you through the process of upgrading your old Trane thermostat to a new thermostat, providing step-by-step instructions and essential tips to ensure a successful installation.

Read also: White Rodgers Thermostat Wiring to Nest [How To]

Old trane thermostat wiring Color Code

When replacing an old Trane thermostat with a new one, it’s important to understand the old thermostat wiring color code. Different wire colors  correspond to specific functions in your HVAC system, and knowing how to decipher them is crucial for a successful installation.

On your old trane thermostat wiring, you will typically find wires and terminals labeled as

X1/X2, W, B,O,G,R,Y

The most important thing to note is what each wire label stands for. When you know this then you can are you old trane thermostat to any new wifi smart thermostat.

old trane thermostat wiring jpeg e1681813228763

Wire LabelMeaning 
X2Back up or Emergency Heat
WHeat stage 1 
BBlue  C-wire or Common)
GGreen (Switched Fan relay, main blower)
R24 VAC from the Transformer
TOutdoor temperature compensation for heat anticipator
FFault light

The T terminal on old trane thermostat

The terminal was an outdoor compensation for heat anticipator in heat pump mode and usually it went to the thermostat. You   wont need  to wire this on a new programmable thermostat and you will have to tape it off.

X2 Wire

The X2 wire on old trane thermostat was for emergency heat. On the New thermostat, this wire should typically be for onE or AUX depending on the brand of your thermostat.

O Orange Wire

This wire is typically used to control the reversing valve in a heat pump system. It determines whether the heat pump operates in heating or cooling mode.

 The O wire will typically go on the O/B terminal of your new thermostat

The B wire on your old trane thermostat is commonly used as the C-wire, which stands for “common” wire.¬†

Read also: How to wire a coleman mach thermostat

The B wire should go onto The C terminal of your new thermostat   The C-wire is used to provide a continuous 24-volt power supply to the thermostat to power its display, programming, and other features, without drawing power from the other thermostat wires.

G Green Wire

This wire is used to control the fan or blower in the HVAC system. When the thermostat sends a signal to the G wire, it turns on the fan or blower for air circulation. G wire from the old trane should go on the G terminal of your new thermostat

Y Yellow Wire

This wire is used to control the compressor in a cooling system. When the thermostat sends a signal to the Y wire, it activates the compressor to start the cooling process. This should also go on the Y terminal of your new thermostat.

R Red Wire

This wire is typically used as the power or “hot” wire, supplying 24-volt power from the HVAC system to the thermostat. It is also sometimes used as the common wire in a system that requires a separate common wire. 

In newer thermostat you would normally have the RC or RH terminal. You may have to connect the R wire to any of the two terminals. However  may need to put a jumper between the RC and RH terminals with an exception of Nest thermostats which dont require jumping wires.

W White Wire

 This wire is used to control the heating system. When the thermostat sends a signal to the W wire, it activates the heating system, such as a furnace or boiler.The W wire from your old trans typically has to go on a W terminal of your new thermostat.

U terminal

 This terminal is left empty and not used in a typical Trane thermostat wiring configuration.

Trane Weathertron Baystat240 Wiring to Honeywell WiFi thermostat

Upgrading from an old Trane thermostat to a new Honeywell Wi-Fi thermostat can offer homeowners increased energy efficiency, convenience, comfort, smart home integration, access to advanced features, and future-proofing for their HVAC system.

 Honeywell Wi-Fi thermostats provide remote control, modern design, intuitive user interface, and compatibility with smart home systems, making them a popular choice for homeowners seeking to upgrade their thermostat technology.

Here is a chart for the old Trane Weathertron Wiring to Honeywell WiFi thermostat

weathertron 2
Old Thermostat WiresColorNew Honeywell Thermostat 
Power from transformer
X2Auxiliary heatE/Aux 
YCompressor relayY
GFan G
OReverse ValveO/B
BCommon WireC
  • Not that  X2and W connect to E/Aux
  •  B connects to C

Final thoughts

Upgrading from an old Trane thermostat to a new one can be a straightforward process, but it requires understanding the differences in wiring conventions. 

With proper installation, a new thermostat can offer improved functionality and energy-saving features for better comfort and efficiency in your home.

Additional resources

Read also: Amazon Smart Thermostat Wiring Diagram for Heat Pump [Full Guide]


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