It's that time of year when the air conditioner is running which means the primary drain line will have a steady stream of condensate running through it. If you don't know where this drain line starts and ends then I suggest you find out before you have a clogged line and possible water damage! (Call me or another qualified professional if you need some assistance.)
Why does this drain line clog up and how can you prevent that?
Air is drawn into the system through the return air filter, any air that gets through or bypasses the filter will have dust & debris. Your home's air is cooled when it passes the cold evaporator coils and moisture condenses there. The moisture removed from the air along with some of the dust & debris will hopefully drip away and never be seen again, right?!?! Maybe. Condensation flows out through the primary drain line seen exiting the side of the air handler and should be covered in pipe insulation. Hopefully there is a short section of PVC standing up vertically with an open end.
If you pour a cup of bleach down this open pipe every spring you will help prevent a clogged drain line. Mold, mildew and algae grow in the pipes and if allowed to coat the inside it can build up along with the dust and debris to eventually stop the flow of water. The bleach will control the growth to keep your line clear.
If you have a sink with a black rubber hose attached to the drain line, this is likely the end of your condensate line. If the drain line is not managed then the P-trap can become blocked at this location. Condensate could then begin to rise in the sink and overflow onto the floor, if you don't realize this in time there could easily be major water damage to repair.
If your termination is at a second floor sink drain then double your repairs!