The condensation pipe leaks because the cool water running off the air conditioning is remaining within the pipe. The clogging can be caused by several different things, such as dirt or debris building up within the condensation pipe. The cool water causes condensation to develop on the outside of the pipe, making the pipe leak water.
The air handler in the air conditioner is a device that circulates the air inside the unit. Negative pressure is created by the air handler. The buildup of this type of pressure can cause air to blow back into the condensation pipe. Once negative pressure enters the condensation pipe, the excess water cannot flow freely through the drain reservoir and into the drain pan. The cool water causes the outside of the pipe to condensate and leak water.
Most air conditioners and condensation pipes have a P-trap located in the drain reservoir. The P-trap is an S-shaped pipe that looks like the drain pipe found under a kitchen sink. The component prevents outside air from blowing into the drain reservoir and into the condensation pipe. If there is a problem with the P-trap, air can penetrate the condensation pipe and prevent the excess water from draining properly. Standing water within the condensation pipe can cause it to leak.
The condensation pipe is connected to other pipes, such as the P-trap and drain pipe. The connection is generally done by soldering the joints together preventing water leaks. If the soldering is defective or damaged, water can leak from the condensation pipe at the point it joins with the other pipes. The water-tight seal that soldering is supposed to create is not preventing water from leaking at the pipe joints.