Blown Heater Hose
 

Several months ago my heater hose blew (the end that attaches to the firewall) in my 1992 190e 2.3. I cut and capped off that hose and the the other one until I could get a replacement. It was the middle of the summer and with no need for a heater, I didn't replace it until just recently. I also replaced the thermostat and a couple of other hoses. Now, I have heat coming from the outside vents, the windshield, but not from the center vent. Does anyone know what's causing this?

This reason for this is that it is the way MB designed it. The center vents are never heated. There is an explanation in the owners manual. I guess you are supposed to close the vents manually when you don't want cool air.