Thanks for the detailed response. I think you may be right. If the problem was in the coolant control valve, bith sides would be warm, but even so, with the temp control knob all the way to CCW, there should be no warm air mixed with the cold air if the flap was closed off fully. I'll check the cables and the flap. The problem occurred quite suddenly. One day the air was cold out of both vents, then next day one cold one not. I had adjusted the RH side temp control knob in the mean time too.