I have noticed that when the "heat is on" there is nothing coming from the central vents. The heat just comes out of the driver and passenger vents. I have made sure the center vent is open. My ACC is set for AUTO.
Centre vents do not operate when max heat is set. A saftey feature I suppose (so you don't burn your face). You can also fiddle with air distribution ubder the profiler. Climate System -> Air Distribution -> Manual -> Panel
The ACC will direct almost all air to the panel vents when Panel is selected.
When Auto is selected the distribution is determined by the profiler. You can change that in profiler.
And according to WIS. When starting in the cold, the defroster vents open first, and then when the temp has reached 45*F the floor vents will open. No mention of the centre vents. Suppose a blast of cold air in the face is not nice.