Take note of irregular spikes in utility bills, too, which could indicate a faulty appliance. Woodbury, MN air conditioning systems usually run up a high bill during summer because of the warmer climate. However, the amount should still be fairly consistent. Compare notes with neighbors who have similar house sizes and AC systems.
Puddles around the central AC unit may indicate that water is leaking, not flowing. Finally, don’t take any chances on a 10-year-old or older AC system; aging systems usually cause surprise problems.