Do the grates shake well? You should shake it down until you see some small glowing coals dropping into the ash pan, you aren't done shaking until you see them. Before you shake, open the ash door and pull out the tray a little and let the fire heat up for a few minutes and then shake. Never shake a cool fire! You must empty the ash pan too. This is where the air comes to feed the fire, you don't want to choke it off with ash. Never leave it full. After shaking, bank the fire with a small rake or hoe to get some hot coals to the top of the box and put the fresh coal into the depression you made. Just putting the coal evenly across the top may be smothering it. I'm not sure about the Harmon but most you bank to the door and then fill it at the rear. You need an active fire on the surface, that is why it has to be banked.
I notice your unit is 8 years old. I would recommend that you check the door gasket. You can use a cigarrette or candle to check. Just run it around the door where it meets the stove to see if it draws the smoke or flame. Overfire air is a no-no with anthracite. The gaskets are common and can be purchased almost anywhere that deals with wood/coal units.