The standard code is red is power or [R] on your t-stat, yellow is cooling or [Y], blue is common or [C], and green is fan or [G]. This is standard across U.S.A. if the installer, installed it correctly. I as a rule of thumb look in the air handler to make sure the colors are correct. I always tell my techs. that elec. doesn't any color and this could you from burning up your t-stat. Plus, while your in the a/h you can make sure your blue common wire is connected. You will need this to run your programmable t-stat. If you are replacing a reg. t-stat then it might not be in use, but without it your running the t-stat on battery back up.
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