An air conditioning system, comprising: an air handling unit configured to control outdoor air that is externally supplied, exhaust air that is discharged from indoors to outdoors, and return air that is circulated indoors and supplied again, control the outdoor air or mixed air of the return air and the outdoor air at a set temperature, and supply cool/warm supply air indoors; at least one outdoor unit configured to supply a heat source for a heat exchange to the AHU; a controller configured to receive operating state data of the AHU and control an operation of the AHU through communication with the outdoor unit; and an interface unit connected to the controller and configured to output a control menu of the AHU, send data received through the control menu to the controller, and output a monitoring screen for the operating state of the AHU and the outdoor unit, wherein the controller is configured to send the operating state data of the AHU to the interface unit and sets the operation of the AHU in response to data received from the interface unit, wherein the controller comprises: a main unit configured to control the operation of the AHU; an input/output unit configured to be connected to devices comprising sensors, valves, and dampers included in the AHU and configured to transfer a control command of the main unit and input data of each device to the main unit; and a communication unit configured to communicate with the outdoor unit, characterized in that the interface unit is configured to be mounted on the controller and is attachable to or detachable from the controller; and the interface unit is configured to display a flow of the exhaust air, the outdoor air, the return air, and the supply air of the AHU on the monitoring screen, wherein the controller further comprises a driving unit configured to control a rotation operation a fan included in the AHU, and wherein, if abnormality occurs in one of the fans, the driving unit controls to stop the operation of an abnormal fan and prevents the abnormal fan from rotating through electrical or physical locking. an air handling unit configured to control outdoor air that is externally supplied, exhaust air that is discharged from indoors to outdoors, and return air that is circulated indoors and supplied again, control the outdoor air or mixed air of the return air and the outdoor air at a set temperature, and supply cool/warm supply air indoors; at least one outdoor unit configured to supply a heat source for a heat exchange to the AHU; a controller configured to receive operating state data of the AHU and control an operation of the AHU through communication with the outdoor unit; and an interface unit connected to the controller and configured to output a control menu of the AHU, send data received through the control menu to the controller, and output a monitoring screen for the operating state of the AHU and the outdoor unit, wherein the controller is configured to send the operating state data of the AHU to the interface unit and sets the operation of the AHU in response to data received from the interface unit, wherein the controller comprises: a main unit configured to control the operation of the AHU; an input/output unit configured to be connected to devices comprising sensors, valves, and dampers included in the AHU and configured to transfer a control command of the main unit and input data of each device to the main unit; and a communication unit configured to communicate with the outdoor unit, a main unit configured to control the operation of the AHU; an input/output unit configured to be connected to devices comprising sensors, valves, and dampers included in the AHU and configured to transfer a control command of the main unit and input data of each device to the main unit; and a communication unit configured to communicate with the outdoor unit, characterized in that the interface unit is configured to be mounted on the controller and is attachable to or detachable from the controller; and the interface unit is configured to display a flow of the exhaust air, the outdoor air, the return air, and the supply air of the AHU on the monitoring screen, wherein the controller further comprises a driving unit configured to control a rotation operation a fan included in the AHU, and wherein, if abnormality occurs in one of the fans, the driving unit controls to stop the operation of an abnormal fan and prevents the abnormal fan from rotating through electrical or physical locking.