An air conditioning system, which can automatically remove a malodor generated due to condensate water remaining in an evaporator during a predetermined period of time after operation of an air conditioner or turning-off of the air conditioner and control a filtering mode time of a filter to filter an air. The air conditioning system characteristically comprises a shiftable deodorization filter (30 or 40) located on a flow channel of the cool air passageway and operationally moved to a filtering mode position so as to screen the flow channel of the cool air passageway during a predetermined period of time after an air conditioner is turned on or off, whereby the air passing through the cool air passageway C and a malodor contained in the air are filtered.