Basic Thermostat Wiring Colors - Air Conditioner Systems - Always remember when changing a thermostat for a new thermostat to take a photo of the colors and where they go on the old thermostat or get a pencil and paper and write it down. It is better to take a good up close photo of the old thermostat and what terminals the colored wiring are terminated. Nearly everyone has a camera on their cell phone.

Basic Thermostat Wiring Colors - Air Conditioner Systems

See the important notes below for further instructions – Thermostat Wiring Colors

Basic Thermostat Wiring Colors – AC Systems Control Diagram

Thermostat TerminalWire ColorWhat is Does
RRed24 Volts AC/Heat Single Transformer
RCRed24 Volts for Dual Transformer – AC♦
RHRed24 Volts for Dual Transformer – Heat♦
GGreenBlower Fan Control
Y1YellowCooling Terminal – Condenser Control
Y2Light Blue but Varies♣Cooling Second Stage
W1WhiteHeating Control
W2Brown or Black but Varies♣2nd Stage for Heat
CDark Blue but Varies♣Common

See our other thermostat installation advice articles.

Notes on Thermostat Wiring Colors:

♦Some HVAC systems will have a two transformer set up. A 24 Volt transformer for the air conditioner and one for the boiler or furnace. If you have a dual transformer system then you need to use terminals RC and RH. RC is for the air conditioner and RH is for the heating system.

♣The thermostat wire colors for these terminals will vary depending on the installer of the HVAC system and if they used conventionally accepted colors for that terminal. This is why it is good to take a photo so you get it right the first time. You don’t know who wired the old thermostat and if they used conventional colors.

For additional wiring for air conditioners you can visit our other articles in the thermostat category.

Basic Thermostat Wiring Colors - Air Conditioner Systems

Basic Thermostat Wiring Colors - Air Conditioner Systems

To learn more about heating systems and HVAC use this resource.

If you are purchasing new HVAC equipment don’t forget to check out our HVAC Consumers Buyers Guide Category for lots of help.

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