[pjbgravely]

I have just discovered on my new short commute (19 miles) that having the A/C on verses having the windows open is 5 MPG less on the scan gauge. My normal commutes are on the interstate at my top MPG speed of 72 MPH. In the summer during heat waves with the A/C on I got 29 MPG on E0 and 28 MPG on E10 unmoded. I also did A-B testing on the interstate and A/C beat windows down at 72 MPH.

My question is has any one else seen this. My choices on what is causing this 1. the A/C compressor is dying, 2. The slow speeds I run on the commute ( 60 MPH max) makes opening the windows a much less aero hit, or 3. something I haven't thought of. I do have a steep hill to climb at the start of the return journey that may be influencing this different. 30 MPG with windows open, A/C off and 25 MPG with windows closed and A/C off.