Sunlight on Thermostat
Sunlight shining through windows can warm interior surfaces dramatically. If your central air conditioner's thermostat is located on a wall that receives direct sunlight, you could see improper cooling by your air conditioning unit, since the thermostat temperature is what the unit uses to determine when to turn on and off.
For example, if the morning sun comes through a window and strikes the thermostat directly, the thermostat could heat up several degrees and cause the air to turn on even though the overall actual temperature in the house may be below the desired level. This could cause the house to get overcooled or even cold in the morning as the air conditioner works to cool the thermostat down to the set level.
If your lawn is filled with shade trees, blocking sunlight from direct contact with windows, walls and parts of the roof, the air conditioner will not have to work nearly as hard to keep your home cool. Heat from the sun can be absorbed by walls, roof shingles and windows.
This heat is quickly redistributed inside the home, which causes your air conditioner to come on more often or run longer to maintain a comfortable indoor climate.
Power Shortage or Outage
Perhaps the most indirect way that sunlight affects air conditioning is the increased demand for air conditioning when the sun causes extremely hot temperatures. During hot and sunny weather, more people tend to turn on their air conditioning and often turn the temperature setting lower to get relief from brutal conditions outside.
This leads to power shortages that can, in extreme cases, lead to outages, because there simply isn't enough energy available to go around. When the power goes out, your air conditioning doesn't work at all.
Sunlight on Outdoor Unit
If the sun shines directly on your outdoor air conditioning unit during the day, you can suffer a 10 percent loss in efficiency, according to the US. Department of Energy website.
The condenser unit simply has to work harder when it is hot outside, resulting in higher energy use. A shade tree to block out the sun during the heat of the day could reduce the surface temperature by up to 25 degrees Fahrenheit.