Leftover AC

In the summer, when you drive somewhere, go inside, come back to your car and find its still comfertably cool from the AC on the journey there. Also works vice-versa on heat in the winter.

*Jim walks back to his car after buying soup in the hot summer*
"Gosh, my car is still nice and cool! Its the leftover AC! Yippee!"

Or

*Shannon gets into her car after buying soup in the freezing winter*
"My car is still toasty warm! Leftover heat!"