The recirc mode on my climate control does not work.I have swapped out the ccu with a known good unit.the accuators work ,and all other funtions of the ccu are fine.I have determined that there is no power at any time to the #6 vacuum switch (in the bank of switches on the transmission tunnel) how do I diagnose this problem?I know this switch powers the recirc accuators ,but I do not know what is supposed to power this switch. thanks for any help 1985 300 sd.

To help diagnosis, the recirc flap should close fully when the engine's running and ACC set to OFF.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD