Well, my new Kilma and aux fan resistor arrived and are now installed. The system seems to work correctly now. I just have to wait until summer to see if the air conditioning can keep up. I am inclined to believe what jhal suggested about the previous PO using a little used car lot engineering to get "ice cold air". If I ever buy another 300SDL, I'll need a week to check out everything I have learned in the past 8 months. However, I love the car.

1987 300SDL (174,000)
1984 190D (305,000)