lancelance

I hard a whirring noise in the passangers side front wheel arch. I pulled of the plastice cover at the front of the wheel arch this leads into the engine but this section seems to be a compartment ie fog light etc(you cannot get to it from the top of the engine). There is some sort of cylendrical motor that runs off the battery. I unplugged this and it stopped. I have driving withhout this for a few days now and engine seems to be working fine ie temp oil etc. Please can sombody tell me what is it and is it important??? Is it part of the aconditioning??