Turn on the fan for Dirac - Go to the red gas control panel. See the sign on the wall - Lobby fan+.
The light is on the sliding lobby fan lever. Push the lever to the ON position by clicking the push skill on the ON word.
Go back up and exit Hall B at bottom of screen. Be at the Entrance Hall. Go down the hall and enter the lobby. See that the fan is still not moving.
Go to storeroom and down to the cellar. Go to the factory circuit left of the hungry monster.
Flip off the left switch of Hall B and flip the switch of lobby using the push skill. Push the lobby lever down.
Go back to Dirac at the lobby and see that the fan is now working.