Why Does a Central Air Conditioner Stop?

Reaching Desired Temperature

• The idea of central air is to have the system do the cooling and the thinking for you. You choose the temperature you are comfortable at, and the air conditioner does the rest. When the temperature in your home gets too high, it turns on and cools the air. Once it reaches the temperature you have set on the thermostat, it turns off to keep the room from getting too cold. If your air conditioner keeps stopping because it is reaching the temperature you have set, all it is doing is working correctly. If you feel the temperature isn’t right when it turns off, check your settings to ensure you haven’t changed it inadvertently.

Short Cycling

• If your central air conditioner turns on and off too frequently, shutting down before the conditions are right, you may have a short cycling central unit. The actual temperature of the air is probably around the number set on the thermostat, but the humidity may make it feel damp and less comfortable in the house. The wrong size central unit often causes short cycling. The size of a central air conditioner is measured in “tons” or “BTUs,” which indicate its power. If the unit is too big for your home, it will cool the air too fast and will not let the humidity be reduced, which is part of the cooling process. The result will be a unit that turns on and then stops over and over again. If your unit is too small, it is likely to run constantly on hot days and waste energy.

Fuses or Breakers

• The reason your central air conditioner may be stopping abruptly, particularly if it isn’t coming back on again, is the fuses or breakers assigned to either the outdoor unit or the indoor air handler. Ensure the breakers aren’t tripped or the fuses aren’t shot. If they are, turn them on or replace them. Breakers will continue to trip if they are not the right size for the job at hand. A 120- or 240-volt circuit is usually sufficient for the indoor air handler while the outdoor compressor and condenser generally require 240 volts.

Fan Motors

• If your central air conditioner still sounds like it’s running but the air is no longer blowing through the vents, the problem is with the fan. While the compressor motor continues to run, the fan motor may be faulty. Without the fan spinning, the cool air cannot circulate. The fans make the airflow possible, meaning they will need to be replaced to cool your home.