In a TDM system, the three-way valve can either send refrigerant to both the fresh food and freezer evaporators in series with each other, or just the freezer evaporator.
So if the control calls for cooling in the FF section, there will also be some cooling happening in the freezer. But if the control calls for cooling just in the freezer, then the FF evaporator will not receive any refrigerant, and there will be no cooling in the FF section until the three way valve changes position.
Does that make sense?