Old A/C use more electricity than old A/C?
Due to advances in technology, newer air conditioners can have a greater cooling capacity for the same ammout of wattage. This means that they will not run the compressor as long, resulting in energy savings.
Also as a unit looses a bit of coolent over time, the unit will run longer to compensate for the loss of cooling capacity causing higher energy useage.
Newer units also do more to de-humidify the air, causing the feeling of comfort at a higher temperature, thus allowing you to keep the t-stat set one or two degrees higher.