Are your brakes working properly?? If so you have vacuum!!
If not check the check valve at the pump outlet. Remove line and remove the fitting below it. You should not be able to see through it. If you can the pieces of the valve are in the pump and its face must come off. Remove the pieces and replace the valve # 004 997 18 72.
Bosch Master, ASE Master, L1
33 years MB technician