[CHICKS]

Things I always found as a tech:

-Poor airflow, such as dirty evap, or filter, blocked return's, and closed off supply's. Filters should be changed 1-3 months depending on how filthy your house is.
-Unrealistic expectations of temperature. Just because the stat will go to 50*, doesn't mean your house will.
-Short cycling the unit. Pick a temp and let it run, quit turning it off and on.
-Dirty or blocked condensing unit. Cottonwood seed is nasty, as is grass clippings. Dirty cond. coils cause high head pressure.