You rely on your air conditioner to keep your home cool during the hot summer months. If your house seems uncomfortably warm even with the air conditioner on, and if the air coming from the registers is cool, you'll have to investigate to figure out the problem. Even with cool air circulating from your air conditioner, it is possible for your home to be hot because of other factors.
Lack of Shading
Some rooms in your house may be hard to cool because of a lack of shading. This is particularly true if a room has an abundance of windows in it. The sun shines through the windows and heats the room. Even if your air conditioner is working as hard as it can, a brightly sunlit room in the summer can still be hot. Blocking the sun from the windows is the best solution to improving the unit's ability to cool the room in this situation. Shading can be accomplished easily with window treatments, or more efficient heat control can be achieved by placement of shade trees between the windows and the harshest sunlight.
Wrong Size AC
Many air conditioners are installed without proper consideration for the correct size, or BTU output. HVAC installers may use a rule of thumb to determine the size you need without considering factors such as the climate you live in. The wrong size air conditioner, especially one that produces too many BTUs, may cool the air but be unable to eliminate the humidity from the air. Humid conditions are perceived by some people as hot conditions. People in the home may feel clammy or sweaty as a result, as the air conditioner will be unable to dry out the air to make it comfortable.
Your home may not be cooled properly because not all of the cooled air is reaching the rooms. A leaky duct system under the home or in the ceilings could allow much of the cold air to escape to the outdoors or between walls. While you may be able to feel cool air coming from the vents, much more of it may not be getting to the interior of the house. Harder to heat areas will then become warmer than they should be, and the air conditioner will have to work much harder to keep up with the demand from the thermostat, resulting in higher energy bills.
Improper ventilation can trap too much hot air in the home, which can make part of your house hot even when the air is on. This is especially true for upper floors. Heat rises, and cool air stays lower. If vents in the attic are not sufficient in releasing the rising hot air, it will become trapped inside the house and result in partial cooling or cooling that will take much longer than average. Also, a downstairs thermostat may detect that the temperature is cool enough to shut off, while there's still plenty of warm air upstairs.