Compressed air supply system for operating a pneumatic installation in a pneumatic system of a vehicle , comprising: - a compressed-air feed ; - a compressed-air connection point to the pneumatic system ; - a venting connection point to the environment; - a pneumatic main line between the compressed-air feed and the compressed-air connection point , which comprises an air dryer ; - a venting valve arranged on the pneumatic main line and configured as a pilot valve, having a pilot connection point (240.1), - a compressor having at least one compressor stage (21.1, 21.2), - in addition to the pneumatic main line , a pilot valve and a pneumatic pilot channel that pneumatically connects the pilot valve to the pilot connection point (240.1) of the venting valve , wherein - a pressure-holding pneumatic valve device is connected to the pilot connection point (240.1), which is designed to provide a control pressure (PS) for the pilot connection point (240.1), - in particular independently of a pressure in the pneumatic main line during venting of the pneumatic system , and - the pressure-holding pneumatic valve device can be pneumatically connected to a pressure accumulator via a feed line , characterized in that - the pressure-holding pneumatic valve device has a selection valve for independent connection of the pilot connection point (240.1) in a first operating position (BS1) to the feed line and in a second operating position (BS2) to the main line such that the line , in which the relatively higher pressure prevails, is connected to the pilot connection point (240.1) and the line in which the relatively lower pressure prevails is blocked from the pilot connection point (240.1). - a compressed-air feed ; - a compressed-air connection point to the pneumatic system ; - a venting connection point to the environment; - a pneumatic main line between the compressed-air feed and the compressed-air connection point , which comprises an air dryer ; - a venting valve arranged on the pneumatic main line and configured as a pilot valve, having a pilot connection point (240.1), - a compressor having at least one compressor stage (21.1, 21.2), - in addition to the pneumatic main line , a pilot valve and a pneumatic pilot channel that pneumatically connects the pilot valve to the pilot connection point (240.1) of the venting valve , wherein - a pressure-holding pneumatic valve device is connected to the pilot connection point (240.1), which is designed to provide a control pressure (PS) for the pilot connection point (240.1), - in particular independently of a pressure in the pneumatic main line during venting of the pneumatic system , and - the pressure-holding pneumatic valve device can be pneumatically connected to a pressure accumulator via a feed line , characterized in that - the pressure-holding pneumatic valve device has a selection valve for independent connection of the pilot connection point (240.1) in a first operating position (BS1) to the feed line and in a second operating position (BS2) to the main line such that the line , in which the relatively higher pressure prevails, is connected to the pilot connection point (240.1) and the line in which the relatively lower pressure prevails is blocked from the pilot connection point (240.1). <EOS>