CHEVROLET S-10 DEFROSTER STUCK

I've Done A Little Work On My Truck, But I Am By Far A Good Mechanic. I've Wanted To Fix This For A While, But I Really Don't Know Where...

99 S 10 Heater Wont Come Off Vent To Defroster Or Floor Heat Just Bought The Truck, It Has Been Sitting For A Couple Of Years, I Know The...