Climate Control on 560SL, Newbie Needs Help!

[Alkraut]

I recently purchased a nice 1988 560SL that has been well-maintained throughout it's life, 79K miles, but needs some attention. Great project! When I first checked out the car, the A/C appeared to work, compressor on, lines cold, strong blower, cold air at vents including center, but no heat. I fixed the thermister sensor (which had fallen down) and replaced the dry-rot tube to it. Resistance on it was high, like 20000 ohms, but reduced to about 1500 when heated. I rebuilt the mono valve (rubber disk was ruptured) and now have lots of heat. Now the A/C is not blowing cold. When I turn the temperature knob to cold or max cold, the compressor comes on, cold lines under hood, center vents blow, but no cold air, just heat! I would appreciate any advice on debugging this, or references to past links. I suspect that my control unit may be part of the issue. The buttons and temp knob appear to work, but not logically. Thanks for the help!