Climate Control - Auto - AC always on

I do not see an issue with leaving the AC on in Auto, even though I turn mine off in cold weather.

As long as the cabin temp is lower than your temp setting the system is going to call for heat and not AC. Only if the cabin temp gets above your temp setting will the system call for AC.

If you call for defrost the system will use AC for humidity control whether the AC light is on or not.

In spring and fall moderate temps I like to use outside vent air and not AC to cool the cabin so I leave the AC off but the system in Auto and then adjust the temp up or down to get the air flow from the face vents and the fan speed where I want it.

 

I deliver pizza in my Prius, and I normally turn it off in the winter unless the windows start to fog up, but I have also experimented a few weeks with leaving it on, and have found that if it's cold out and the humidity sensor isn't saying the windows are fogging up, it barely ever runs the compressor. It seems to start it up at very low speed now and then for a few seconds, probably just to lubricate it, but there was no detectable mileage difference and very little noticeable difference in HV drain while sitting. Now I mostly only turn it off when it's a little warmer out and just don't want to use it.