When the AC or the heater is blowing air, all rooms but one have the expected temperature, although not exactly the same, but acceptable. For this particular room (the master bedroom) , when the AC is on, it is much colder than other rooms, and when the heater is on, it is not very warm. When I adjust the damper, the temperature in this room is still lower than other rooms, it is either too cold ( when the AC on ) or not warm enough ( when the heater is on ).
Thanks. It works !!! I thought choking down the other rooms' dampers would make this room colder because it gets more cold air, but surprisingly it really makes this room less cold with A/C, and warmer with heater.
Still don't understand why , but I really appreciate your help.