An air conditioning system has a heat pump, a first-liquid-medium circuit in which a first liquid medium circulates, a second-liquid-medium circuit in which a second liquid medium circulates, a heat source, a connection switching device, and a controller. The connection switching device switches between a connection state in which the heat source is connected to the second-liquid-medium circuit and a disconnection state in which the heat source is disconnected from the second-liquid-medium circuit. The controller controls the connection switching device to switch between the connection state and the disconnection state based on a heat-related physical quantity relating to a heat of the first-liquid-medium circuit, a heat-related physical quantity a heat of the second-liquid-medium circuit, a heat-related physical quantity the heat generated by the heat source, or a heat-related physical quantity a heat of the heat pump.