Yes, if the cold air from your a/c and the warm air from your furnace come out of the same vents, then they are both using the same blower to move the air. Even though the furnace is not producing any heat while operating the a/c, it still delivers the cold air throughout your home with the same blower, and passing through the same air filter. This is why, regardless of the season, you should regularly change your air filters. Note: make sure the unit is not running when you change the filter. Tip: Use a marker to write the date on the side of your air filter when you replace it. Then you won’t have to guess when the last time your filter was changed!