Heater fan problem?

[black haze]

Allright, my a/c works fine, blows cold.The fan never stops blowing if i have it on, like it should.But, when i turn on the heat and pull the lever over to the heat side, my fan stays on for about 5 seconds then dies down to where nothing at all blows.The few seconds that it does blow is not even hot.All the other settings(ac,max ac, vent, and defroster)work perfectly.Anytime i hit the heat button it just stops.Anybody had this problem?And any comments on what to do?
Thanks

 

[Whit]

there is a small door under the dash just above yer tranny hump that should open when you turn it from defrost to heat that sounds as if it aint openin............its vacumn controled so you may have a hose of OR lost yer vacumn supply from the vac pump under the hood