If you get regular preventative maintenance on your air conditioner, you may never have to worry about a dripping AC.  Your overflow drain pan should have a float safety switch that is designed to cut off your unit if the water level gets too high.  Older systems did not require the float switch but any equipment replacement should now ensure that you have this switch installed.  Preventative maintenance includes verifying that your drain line is properly draining.  Most times your technician who will catch the problem that may lead to the telltale drips inside your HVAC and around the floor, ceiling, or walls.  But just in case you do experience this kind of leak; call for help right away.  You do not want to let this kind of problem go unattended, as damage to drywall and floors could result.  If the leak is more than just a small drip you may be advised to turn the unit off until a technician can get their to mitigate any damages.

Here are some of the causes of a leaking and/or dripping AC.

1. Clogged condensate drain line. This happens when the moisture removed from the air on evaporative coils flows as condensation into a pan and out a drain line. Over time, the line can become clogged with dust, loose insulation in an attic and algae that turns into gunk, resulting in an obstruction in the line.  Regular Preventative Maintenance by a professional HVAC tech can verify the proper draining of the condensate and remove any obstructions and/or treat of any algae while doing the service.  If you want to tackle it, find the pipe near the drain pan (look for a piece of pipe at a 90-degree angle with a cap on it referred to as a cleanout). Take off the cap and pour vinegar down the drain line. This should keep the line algae free if you do it every couple of months.  If you have an older system you may NOT have the cleanout and should proceed with caution if you do not have a float safety switch on the pan.
2. Frozen evaporator coils. These coils, located near the air handler, are key to removing moisture from the home’s air during the cooling process. Often, when the coils or the air filter is dirty, the coils will freeze up due to poor airflow. The moisture isn’t being removed properly and there can be overflowing and dripping.  Remember to change 1″ filters monthly and have your system serviced at least twice a year to check for dirty coils.
3. Cracked or overflowing drain pan. The drain pan collects the condensation mentioned above, which is sent out of the house through the drain line. The pan can become cracked or a clog can cause overflow, which can result in water stains and puddling. The drain pan may need to be replaced.  Most systems have two pans.  The factory installed pan at the coil (which may be plastic or metal) and a secondary pan which is usually metal located under the equipment.  With age the pans can crack, rust, or separate so regular maintenance is a key to preventing this unforseeable threat.