Anyone have any insight into heating/air conditioning?

[ggspeed]

I have a 1987 SDL. Great car, a/c blows "cool" and heat works fine. However it seems to be stuck in defrost. Even set on regular heat/air conditioning settings, the air will not blow out of the front center vents. It confuses me because it will blow out of the rear vent the side vents and just stay blowing out of the defrost vent on all settings.

If anyone has had this happen to them or might know how to fix it please let me know.