1993 190E A/C, Defrost and Heater Air Duct fan speed increases but air isn't blowing at the proper volume. Just bought the car and not sure how long it's been doing it. Have a friend with the same model which air duct blowing velocity is much higher. You can hear the fan speed increase when changing the switch, but the volume of air only increases slightly. Cooling temp is fine.

It seems as if the ducts are restricted.
Is there a filter which may be clogged?

Thanks in advance for your help!