The Ventilation System is a major mechanic in Five Nights at Freddy's 3. In the game, all of the phantoms can cause this system to be disabled, meaning that Phantom Freddy Phantom Foxy, Phantom Chica, Phantom Balloon Boy, Phantom Puppet, and Phantom Mangle can all disable the ventilation. In order to turn it back on you must go to the error menu and either reboot Ventilation or all systems.