Another 200 heater problem

Right its a 1991 Discovery TDI with a/c
My problem is iv just managed to get the blower working, but i can't get any air threw the windscreen vents. Iv searched the forum, and the only thing i can find is something about a vacuum pipe, but not very clear about this.

Right been messing about with the heating in the car, with the temp set at hot or cold with the blower on i get cold air out of the front of the dash. When i switch it to windscreen i get nothing,on hot or cold. If i turn the blower off, while driving along at a good speed i get hot air coming threw at the screen. Anyone have a clue whats going on.

I am a tad confused, iv seached the forum, can somebody just clarify, the blower in the passenger footwell is for the air con only. Reason being iv just taken it to a supposedly land rover expert in medway, and he tells me the blower in the footwell is for the heating, and that there is definitely no blower under the centre of the dash, he says he has looked. Well i have looked, and i don't think you could tell that there was nothing in there without removing the dash. The pipe work does not look right for the blower in footwell to do hot.

Well, thanks for all the reply's. Bit the bullet and removed the dash, don't no what i was worried about, 50 minutes, no drama's, just got to put it back now once iv picked up a new fan.