Do you have vacuum in both lines when the blower isn't working. You need to tee into the line. If you have vacuum on both sides then you need to find the blower vac switch and see if vacuum is getting to it.
Bypassing the electrical portion of the swicth will undoubtably give back your blower functions. Try it as a test. Unfortunately you can't just leave it bypassed as you will find that the system can not be turned off in that case. You will need a vacuum schematic to find the leak.
Bosch Master, ASE Master, L1
33 years MB technician