Air not coming from vents, W reg Micra?

My 2000 Micra's fan works very well, on all settings, however no, or very little air is coming out of the vents. The switch to change from external to recirculated air operates ok, seen the pad change from one to the other....... But, on recirculated air blasts from the duct under glove box........ I think that the polarity may be reversed, but can't find anywhere that this can have occured