referring now to the drawing figures , fig1 and 2 show exemplary embodiments of compressed air brake systems for a service brake in a motor vehicle . a brake control device 10 with closed - loop braking intervention control system , analogous to an abs or ebs , directly reads out data from wheel speed sensors 11 , 12 at driven wheels 13 , 14 and from wheel speed sensors 15 , 16 at following wheels 17 , 18 . the brake control device actuates in a known fashion pneumatic valves for regulating the function of compressed air brakes ( not shown ). these pneumatic valves are referred to here as modulators 19 , 20 . in the embodiment depicted in fig1 , the brake control device 10 is connected via a can bus 21 to a control device 22 for an air conditioning system . alternatively or additionally , the control device 22 can be provided for a compressor controller . the switching over of a compressor 23 between feeding mode and idling mode is controlled by a solenoid valve 24 , which , for reasons of better clarity , is shown adjacent to a solenoid valve 25 and near to the control device 22 , but can also be integrated in the compressor . the solenoid valves 24 , 25 are actuated by the control device 22 . the solenoid valve 24 serves to control the compressor via a pneumatic control line 26 . at the same time , the solenoid valve 24 is connected to a sound damper 27 . electrical control lines for the solenoid valves 24 , 25 are denoted here by the reference numbers 28 , 29 . the component of the compressed air brake system is also an air dryer 28 , which typically contains a desiccant in the form of a dryer cartridge . a line 29 leads from the air dryer 28 via a non - return valve 30 to a multi - circuit protection valve ( not shown ) with storage containers for the compressed air ( see arrow 31 ). a line 32 also branches off to the solenoid valves 24 , 25 downstream of the non - return valve 30 . the solenoid valve 25 is connected via a line 33 , with throttle 34 and non - return valve 35 , to the line 29 upstream of the non - return valve 30 . the solenoid valve 25 is also connected to the solenoid valve 24 and to the sound damper 27 via a line 36 . between the compressor 23 and the air dryer 28 , a line 38 branches off from a line 37 to a purge valve 39 , which is connected to the sound damper 27 via a line 40 . the purge valve 39 is controlled by the pressure present in the line 33 ( see pneumatic control line 41 shown in dashed lines ). in order to regenerate the air dryer 28 , the solenoid valve 25 is activated and assumes the position shown in fig1 . as a result , the pressure from the storage container or from the line 32 is present on the line 33 . the purge valve 39 is correspondingly moved into the position whereby the lines 38 and 40 are connected . furthermore , compressed air expands at the throttle 34 and flows through the air dryer 28 , picks up the moisture there and passes into the open air via the lines 38 , 40 and the sound damper 27 . the control device 22 controls the function of the solenoid valves 24 , 25 , as stated above . the information , which is made available via the can bus 21 and is available in the brake control device 10 and / or information originating from other control devices can be taken into account in this context . an important function of the control device 22 is switching the solenoid valve 24 as a function of a minimum lower limiting value of the compressed air in the storage container ( not shown ) or in the lines connected thereto . the minimum lower limiting value is not predefined statically here but rather calculated dynamically , in particular in the brake control device 10 , and on the basis of the determined values of the wheel speed sensors 11 , 12 and 15 , 16 . the values supplied by the wheel speed sensors 11 , 12 and 15 , 16 can also be included in the control of the air conditioning system , that is , in the switching of the valve 25 and the regeneration of the air dryer 28 . the difference between the embodiments depicted in fig1 and fig2 is the arrangement of the control device 22 . the latter is not shown in fig2 . all the functions of the compressor controller , including the air conditioning , are triggered by the brake control device 10 in fig2 . the lines 29 are correspondingly connected directly to the brake control device 10 . it will thus be seen that the objects set forth above , among those made apparent from the preceding description , are efficiently attained , and since certain changes may be made in the above constructions without departing from the spirit and scope of the invention , it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense . it is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which , as a matter of language , might be said to fall therebetween .