[TimV]

I use this rule. No AC on backroads. Roll down your window. Only AC on on the highway. Open windows then increase draft so more fuel use then you would have with closed windows and AC on.

I burn 7% more fuel with AC on on the highway.

The AC cycles automatically on and off once the temperature in the cabine is lowerd.
When you cycle the AC, when you switch it of, you get some redt cold out of the system.

When i need to brake, or DFCO, I put the AC on on full blast. Getting some regenAC