heater was working great,now its almost like the flapper door is not working properly.will throw a little heat sitting in park,very little.going down the road none at all.already changed the thermastat 195 degree,both heater core hoses are hot to the touch,leading me to believe it is circulateing throw the heater core.Is it possible something fell down the defrost vents(pens ,pencils) and is blocking the flapper from closing.