Look first at the linkage between the lock mechanism and the vacuum actuator. The switch for the pump control is in the actuator. Since the pass side works the system then the vacuum is working. When one uses the key one moves the actuator which moves the switch in that device and activates the pump for the rest of teh system. You either aren't moving the actuator in the drivers door or the actuator switch is bad or it is unplugged.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician