There is a vacuum servo at the front right of the trans. With vacuum applied a fulcrum changes position and causes the effect of the control pressure cable to change (making the shifts last longer for a given time on each start up). On the bigger cars the time interval is controlled by engine temp. On the C220 it is a straight timing issue.
The switchover valve at the right rear applies the vacuum to the servo under the timed interval. Try applying vacuum to the line from the switch over valve (to the trans cable servo). It should hold. Try seeing how much vacuum is at the switchover by teeing a vacuum gauge to the input to the switchover valve. If you have vacuum then try teeing after the switchover and see if the vacuum appears and holds till the time interval passes at which time no vacuum should go to the cable servo.
Bosch Master, ASE Master, L1
33 years MB technician