While your air conditioning system cools the rest of your home adequately, one room in your home remains hot. There could be multiple factors working in conjunction to cause this disparity, or it could result from a single issue. Possible causes include:
Problems with the air conditioning system
Your air conditioning system doesn't consist solely of the unit outside on the concrete pad. If the cooling problem is isolated to one room, the unit should be functioning properly. Your problem may lie in the air delivery system of ducts and vents that carry the chilled air to the affected room. Check for issues such as:
Sometimes the simple solutions are the correct ones. Check the vent in the hot room to be sure that furniture, rugs, or clothes are not blocking the wall or floor vent. If the vent has a manual shutter for blocking it off when the room is too hot or cold, check to see that it is open and that you can see inside the duct.
Volume damper malfunction
Volume dampers are used to regulate the flow of air within a line of ducts. They are usually found on the side of a piece of duct, near the plenum that sits atop the furnace, but they could be located elsewhere. You will see a metal handle that sits atop a dial that reads "open" on one end and "shut" on the other end. However, sometimes the dial is placed incorrectly, so check the direction of the handle.
If the volume damper is installed correctly, the volume damper should be fully open if the handle is parallel to the duct. If the handle is perpendicular to the duct, the damper should be closed, allowing little or no air to pass through.
If you can't feel air coming from the vent in the affected room, and the damper appears to be open, use a pair of pliers to turn the square rod to which the handle is attached. The damper could be stuck tight and the handle stripped and broken, and will need to be turned manually ninety degrees in either direction.
If the affected room or the section of the home is an addition to the existing home, the installed ducts may be too small to handle the necessary air flow. You will need to contact an HVAC contractor to determine if the ducts are properly sized and to replace them if necessary.
While some of the preceding issues may be causing part of the problem, the room may just be located in an area of the house that receives an excessive amount of sun. You can help to keep the room cooler by using room darkening shades at the time of day when the sun is most intense, and well as planting shrubs or small trees that may block some of the sun's rays.
You can also opt for a portable air conditioner if you don't like the noise and appearance of a window unit. Most portable units are on wheels, so they don't need to be lifted. You will still need to vent the portable unit out of a window with vent hoses, but they are generally not as obtrusive as window units. Choose the slightly more expensive two hose model if possible, which cools more efficiently and removes moisture to the outside instead of into a storage tank in the unit that must be drained often in hot and humid weather.
Contact a service like Wright Total Indoor Comfort to learn more.