2008 Toyota Prius Owners Manual - Page 246

3-2. Using the air conditioning system and defogger n Operating conditions The "POWER" switch must be in the ON mode. CAUTION n When the outside rear view mirror defoggers are on (vehicles with mirror defoggers) Do not touch the rear view mirror surfaces, as they can become very hot and burn you. NOTICE n To prevent 12 volt battery discharge Turn the defoggers off when the engine is not running. 218 PRIUS_U_(L/O_0802)