I've tracked Commissioner Gordon to the mall. I've opened the door and taken out the first round of goons with the Batmobile's, disabled the first ventilation fan, taken out the second set of goons across the ventilation shaft.
Now I find myself riding the elevator up and down looking for a way to the second power source under the second fan. I've tried shooting the fan's power source with the REC gun through the fan with no success. I've tried using the explosive gel to destroy the weak wall at the bottom of the elevator, but Batman just shakes his head at me in disgust.
Where do I go from here to disable the second fan?