[Andras]

Mark, You have to get under the car, and physically move the flapper valves "open" ; they are located near the heat exchangers. Open them, so that you can see the circular "target" to be open. The "trargets" are similar to a drawn circle with an x through the diameters.

When the heat controls are "up", then that should close the targets or flaps. When the heat control is down, it should open the flappers, thus dumping the heated air before it gets to your passenger compartment.

It sounds as if something is stuck down there. You do have to crawl under the car, or have it lifted. The flapper box is towards the front of the heat exchangers, not a part of them.