I don't know how the 190 works, but there is a description of when air is supposed to flow from which vents at the thread

http://www.peachparts.com/shopforum/showthread.php?threadid=12508

This implies that there should occasionally be times when there is reduced or no airflow from the center, at least on the 300Es. Good luck.

__________________
John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E