Written As others have said, what you are asking about is commonly called economizing of free cooling.  Most window A/C units have this function, though they don't always explain it.The mode is usually called, "fan only" or "Energy saver mode".  Usually, this means the fan just runs to bring outside air in or in a more expensive unit, a thermostat will decide if the outside air is cooler than the inside air.A word of caution, the outside air may be cooler but if it has significantly more moisture, it may have more embedded energy than the air inside.  Warm and dry vs. cool and humid.Written Written This function is called "free cooling" and can be applied to Central Air Handling Units (AHU's)In AHU applications there is always a controller measuring outside temperature and room temperature. Whenever the outside temperature is better than the inside temperature (depends on whether you are in heating or cooling mode) the controller will start the fans and exchange air from inside to outside and vise versa.