I've got a 1991 3.1v6, and I don't have heat while driving, and not much air comes out of the front defroster vents. Every function is in working order besides the defrost. And when I switch it to defrost, the actuator moves as it should. I have also checked and the doors inside the heater box are not jammed or anything. And there seemed to be nothing blocking the duct work. The air conditioning functions are fine, and everything seems to be working as it should. I just don't know why not much air is coming out of the defroster vents.