Cant see out windscreen?

hi all hope you can help i have a 2.5 diesel 1998 i had all 3 blend motors replaced about 5 weeks ago turn heater on full nearly blows you out the seat lol but my problem is nothing comes out the screen vent drivers side so i cant see a damn thing unless i wipe it or look out passengers side for about 5 miles yours hopefully nev

It sounds like they didn't fit the ducting back properly.