Air supply device for a vehicle

The air conditioning system (1) has a compressed air inlet for connecting a compressor (2). An air dryer (5) is provided for drying the compressed air entered through the air inlet. A measuring device (32) is arranged in an area (7) after the air dryer for measuring a pressure which is different from the value of the compressed air. A measurement signal (S4) is generated and outputted to a control device (20). An independent claim is also included for a method for verifying the operability of a measuring device in an air conditioning system.