While using the window defroster, use a long press on the fan button to turn HVAC off completely.
If you just press the fan it only turns off the defroster mode, but it will keep blowing. The long press also helps with your efficiency.
This tip is from Ride the Lightning episode 177 by Jonathan from Atlanta and can be found at around 1:06:11 in the episode.
Find this awesome podcast here: https://teslapodcast.libsyn.com