CatTech

I have a '95 Tahoe,now that cold weather has hit my state I have noticed that with the heater on HIGH and no matter where I hadthe **** set for it to come out of...sometimes I get no air from the vent outlets. The blower motor is still running and is changeable through the speeds. Ihave tried to switch the outlet point (IE: floor, defrost, dash vents) and still nothing. The recirculating button doesnt change anything excpet for the sound of the blower motor.When the heater finally wants to blow out....I get heat and cancontrol the outlet point.

ANY IDEAS of what door or switch is bad. Im not against tearing thedash out but Im not into swapping parts.