UPDATE: Hello again, Didn't want to leave everyone "hanging" I still have not been able to fix this problem. To review I have FULL heat which overwhelms the AC system. The heater control valves have been checked and they are working perfectly BUT there is no 12V power getting from fuse #15 (circuit is live) to the center pin of the three pin heater control valve connector.

Now here's something I've been told that surprised me . . . My OAT (outside ambient temperature reading is also not working and displays -36 F. The sensor unit in the front grille has been verified as working properly (swapped out to another SRT6). I went to a local independent Mercedes garage to talk with them and the owner tells me that the OAT system not working is probably related to my AC / Heat system issue. He say's "Why would you need AC when the computer thinks that the outside temperature is -36 F??" That outside temperature system is tied to the computer - it's not just to let you know the outside temperature."

Can anyone confirm that information is correct?? Any new suggestions before I take the car in for "professional assistance"??

Thanks, Bob Davis (Red Dog)