The VCV basically tells the transmission how to shift when the engine is cold or warm. At coolant temperatures below 50 degrees Celsius it increases the amount of vacuum available at the vacuum modulator of the transmission so the transmission will shift smoother when the car is cold. On the old 617 engine cars, the trannys used to shift really hard when cold. At 50 degrees Celsius and warmer, it decreases the vacuum to the vacuum modulator at the transmission and then the transmission will shift a little firmer.

Testing the vcv:
disconnect black/red vacuum line from the vacuum damper, and connect a vacuum gauge and check the vacuum at idle. Value should be 385+or- 20 mbar. with the engine stopped and the throttle linkage at full load stop the gauge should read 0.
if it tests ok proceed on.
not ok; check the vacuum pump or adjust the vcv and replace it.

Testing the temperature switch:
at coolant temps above 50 degrees celsius the ground connection for the vacuum amplifier switchover valve must be opened by the temp. switch.
connect ohmeter between temp switch and ground. value is Infinity. If it is not replace the temp switch.

Testing the switchover valve:
Unplug temp switch and ground the plug. The switchover valve should audibly click.If it clicks the switch is fine. No click, check if you voltage at the plug. If you have voltage but no click, replace the switchover valve. No voltage, you have to trace the wire to see why there is no voltage.

Hope this helps.
You can purchase a repair CD for your car from MBUSA for about $20.00
It has all the adjustment instructions for the vcv there. You really need to see the diagrams also when you try to figure out what is wrong.
Good Luck
John