In Florida,  Air Conditioning systems are most of the time, ran all year round. This decreases the life span of a typical AC unit(which is about 8 -10 years), especially if regular maintenance is not done and or if it is installed directly on the coast.

"When it comes to duct work, there’s lots of discussion  kicking around about them being substantially undersized. Here’s a two-minute test that can check the size and performance of your duct system. The instruments are inexpensive and it takes less than 10 minutes to learn to do."

"Tons of Air Static pressure is a measurement of how hard a fan has to work to move airflow through a duct system. Contrary to what we might imagine, air is really heavy. One pound of air at sea level is the size of a cube measuring 2.5 square feet on each side.  At 2000 cubic feet per minute (cfm), a five-ton fan pushes and pulls 9,000 pounds of air through its duct system in one hour of operation. Seems like that’s surprisingly close to five tons of air per hour, doesn’t it?" Click here for the full article. 

What do think about these statements?