Peugeot 306 heater fan vent stuck shut how do I fix it? ?

My 1996 peugeot 306 DT blew the bulk head resistor which I replaced. Once I replaced it I noticed the fan was working fine but there was no air coming out of any vents. Then the bulk head resistor blew again. I am now told it is probably because the fans vents have got stuck allowing fresh air into the car! Does anyone know how to fix this?