Here is the problem. I like the temp about 70 when I am driving unfortunately this is too cold for my wife who likes to set her side quite a bit higher, usually up around 78. Now that it is cold and we have to use the heater we have noticed that when the car gets up to about 70 degrees or whatever the drivers side is set to on AUTO, then the fan quits blowing and little or no air comes out of the heater vents on her side. If we manually turn the fan on, then she gets all the heat she needs and my side stays confortable too. On AUTO the fan shuts down when the drivers side reaches it's optimal temp. I have tried it with the drivers side set to 60 and the passenger side set to 80 and with the drivers side set to 80 and the passenger side set to 60, in both cases the temp on the drivers side controlled how long the fan stayed on.

Does that sound right. We are new to the car so I don't have a lot of experience with this system. It seems to me that the fan should stay on until both sides are as warm or cold as person wants, and then should slow down or shut off.