Two years ago, my indoor AC unit started leaking water. After a quick internet search, we discovered that you have to keep the pvc pipe drain cleared out. We did so with bleach and had no other trouble. I had occasion to speak to an AC reapair man later. He mentioned something about blowing out the drain line. I have an air compressor and wanted to know if there is a preferred method of doing this; if there is a special fitting for the air hose, etc. Bleach is not working this time.

Put your air pressure on the opening in the tee that is above the pipe goes into the floor. Block off or plug with your finger the other end of the pipe that goes to the inside of the coil. Usually you can just use your thumb to cover over the pipe that goes inside the coil.