Previously I have posted a question why does the AC light is on
whenever I turn on the heat. My concern is the compressor
is always running. A Nissan mechanic told that in this mode,
the compressor will just cycle once in a while to prevent the
AC system from being damaged when not used during the winter.
You could, however, push the AC button and turn this mode off.
But normally I prefer not to circulate air from the outside during
traffic so leaving the AC on will just circulate inside air.

 

The green light means the compressor is enabled, not that it is running. Running the compressor in the winter does have the benefit of keeping the compressor seals lubed but as much as anything else the compressor runs to remove humidity from the cabin.