If your air conditioner or heat pump blower is in your attic or crawl space above the ceiling and you notice water dripping above a window or under the roof line, be careful. This is not normal; you have a problem!
The water that condenses during the normal operation of your unit drain through a pipe that will usually just drip on to the side of your home by the ground. Building codes require that a secondary drainpipe be installed in case the primary drain is plugged with dirty sludge that sometimes forms in the drain line.
This drainpipe is meant to make a noticeable drip on the side of the house that you can see and know that the primary drain is plugged up. Do not ignore this wet window or sometimes rusty looking wall. Damage can occur if the drain is not cleared, not only to the wall surface but if the secondary drain pan rusts out, also to the ceiling.