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Thermostat Wire
Color Codes

Conventional heating, air conditioning and heat pump thermostat wiring labels, wire color codes and the corresponding function description:

Rh Red 24 Volt Hot for Heating
Rc Red 24 Volt Hot for Cooling
Y1 Yellow First Stage Cooling
Y2 Blue Second Stage Cooling
G Green
Gray *
Energizes Indoor Fan
W1 White Energizes First Stage Heat
W2 Black Energizes Second Stage Heat
O Orange Heat Pump
Reversing Valve
Energized In Cooling
B Brown Heat Pump
Reversing Valve
Energized In Heating
C Brown** 24 Volt Neutral
(Common) leg

*     Found in some Carrier furnaces
**    The brown is often the first choice to use for the 24 volt common leg but white, black and blue are also used.


All of this goes out the window if the person before you didn't know or care to use the accepted color codes. Sometimes it is simpler to take down the existing wiring and re-terminate using the accepted color codes than it would be to map a "creative" wiring scheme.