The invention relates to a roof-top air-conditioning system K, particularly for a bus, comprising a series of devices, which are subjected in succession to the action of internal coolant, and which consist of a high pressure-side heat exchanging device including a fan device, an expansion device, an evaporating device and an inner duct arrangement for guiding air, which is to be conditioned and which exchanges heat with the evaporating device. Said high pressure-side heat exchanging device has a modular design. According to the invention, connections for coupling modules of the same type can be provided, are prepared or are formed, and the modules are designed for a grid-like coupling of modules of the same output and/or of modules of stepped output.