An air cleaner and a method for controlling an air cleaner are provided. The air cleaner may include a first air cleaning module having a first fan and a first filter; a second air cleaning module having a second fan and a second filter, the second air cleaning module provided vertically over the first air cleaning module; an air flow controller provided at an upper side of the second air cleaning module and including a circulation fan; a sensor configured to sense a pollution level in a room space; an input configured to receive input of a command for an operation mode of a plurality of operation modes to operate the first and second air cleaning modules and the air flow controller; and a controller configured to drive at least one of the first fan, the second fan, or the circulation fan selectively and determine an amount of discharge air flow. Based on at least one of an operation mode input or the pollution level, the controller may operate one of (1) the first fan, (2) the first and second fans, (3) the first and second fans and the circulation fan, or (4) the second fan and the circulation fan.