The AC (or defroster) will cycle in use (except when AC is on full) and everytime it comes on or off you will hear a click coming from the engine bay. This should happen around once every few minutes. If you hear constant or rapid clicking it may be a sign you are low on refrigerant or you have a problem with the AC clutch (or electrical circuit). My first suggestion is to get your system serviced (evac and refilled) and see if that helps.Originally Posted by cHRiSCOe