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|
|Energizes Indoor Fan|
|W1||White||Energizes First Stage Heat|
|W2||Black||Energizes Second Stage Heat|
Energized In Cooling
Energized In Heating
|C||Brown**||24 Volt Neutral
* 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.