I think the actual value readings will help diagnose your problem quickly. Please refer to the 210 chassis a/c diagnostics article here: Service Articles from Continental Imports Put the control unit in diagnostic mode and post up the values of items 1-8. It may be helpful to post them both when first starting the car and the a/c is cool and also after the a/c becomes warm. I am specifically interested in items #3 & 4, which are the temperature of the right & left heater core - this will indicate whether or not your duovalve is stopping hot water flow through the core.