heating problems
 

I have a 99 Gran Marquis. I just had the heater core replaced and the heat still won't work. The mechanic looked at it again and said he adjusted some door. Idk what he meant by that. Anyway, the heat still does not work. Can someone please offer some help for this? Would a flush of the cooling system help possibly? The mechanic did say that there was so much buildup in the old heater core that it weighed twice as much as the new one.