Don't Stress over a lack of noise...

“Don't judge the efficiency of your air conditioner by the sound of the fan shutting on and off. The blower will continue to circulate cooled air throughout your home up to 15 minutes after the compressor has stopped. (The same holds true for the furnace.) ‘

http://www.powerhousetv.com/Energy-EfficientLiving/Energy-savingsTips/027471