why is it that the ac light comes on in auto climate control?

#1
if i set my climate control to auto for heat (78%) my ac light comes on,I'm not sure if the compressor is actually on ,that's kind of wast on gas millage ,is this normal--2015 corolla s plus ?
 
#2
if i set my climate control to auto for heat (78%) my ac light comes on,I'm not sure if the compressor is actually on ,that's kind of wast on gas millage ,is this normal--2015 corolla s plus ?
In auto mode, the "AC" light comes on only over a certain exterior temp (and so does the "recirculate" if the exterior temp is even higher). For instance, where I am, I never see it between november and april, and that's the moment where my mpg is slightly worst (cold temperature, snow tires, winter gas). Doesn't necessary mean that the compressor is on.
 
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