Nobody wants to see water dripping from the ceiling. Air conditioner pan overflow is a problem in Texas. When both the primary and secondary drains are blocked overflow occurs. Take a few minutes each spring/summer to clean both drains. Bleach in the pan and primary line will help stop mold, mildew and algae from growing. A few seconds of back flush with a garden hose from outside the home will clean the secondary drain of insects that have taken up residency.