Here's a theory that I'm wondering about:
In the winter time, I commonly leave my climate controls set at one of the defrost settings (either full defrost, or the split defrost with half the air blowing at the windshield and half blowing at your feet).
I haven't listened for the compressor yet, but does anyone know if the split defrost setting engages the A/C compressor? On other brands of cars I've had, engaging defrost would automatically turn on the A/C and would light the A/C light so that you'd know it was on. On the Impreza, I know that full defrost engages the A/C (without lighting the A/C light). I don't know if the split defrost engages the A/C.
I wish Subaru would design the car so the A/C light turns on whenever the A/C compressor is engaged, even when using defrost in the winter time.
We all know that driving with the A/C on takes a toll on MPGs. Is it possible that some of you who are unhappy with your MPGs are driving all the time with the A/C compressor on, and don't even know it?