That's okay, dudly. Your 190E heating is working just fine. My '90 190E does the same thing. The center vents do not blow hot air, just the side vents. You have to close them the center vents if you just want hot air. I was told by the salesperson that all M-B do that, or at least the older models. I think the 300E does too. Yeah, I thought something was wrong with the heater when I was testing all the functions. It's normal. Maybe someone can confirm this?

Btw, I hope you enjoy your 190E. It's one of my favorite M-B models.