A compressed-air supply system for operating a pneumatic installation includes a reservoir, a number of bellows, a pressure-air feed to which a charging assembly having a compressor is connected on a pressure-medium feed side, a pressure-air connection to the pneumatic installation, a venting connection to the environment, a pneumatic main line between the pressure-air feed and the pressure-air connection, a vent line between the pressure-air feed and the venting connection and a changeover valve associated with the pressure-air feed and configured to be controlled by pressure air in such a way that the pressure-air feed is open or can be opened via the changeover valve to the main line. A flow pressure at the pressure-air feed can be generated by the charging assembly to the main line.