Or it could be a build-up in the drain tube that is stopping the moisture build-up or condensation from draining.. Although another reason why could be that the water pump may not be working.
The first thing you should do is look to see if one or more of the lines is leaking. If the air conditioner run off pipe is the cause of the problem, you will need to change it, you may buy the lines at an air conditioning supply or at a hardware store. You will also need to purchase the glue for the particular line you have, ensure that you stick to the guidelines.
If when testing the power pump it does not start it’s either broken or stuck. You will have to detach the power pump from the electricity and from the tube, remove the top of the pump motor and clean it out if the pump is stuck. You will learn that if it really is pretty old or broken now is the best time to replace it.
If you find that the water pump is operating but no water is draining the anti siphon might be stuck, it’s located right before the discharge tube. Remove the anti siphon, loosen the ball inside, and look for an obstruction. If it appears that a moisture build-up or condensation run off pipe is clogged with green blue scum, remove it if at all possible (you may need to cut it and replace it later with a coupling). I like to recommend replacing the line, but you can blow it out or run a wire through it to clean it out. If you’re not going to replace the tube you simply must kill the blue green slime, combine a bleach solution and run in through the entire power pump.
If none of the above situations are the problem you most likely have ice building up this can and will block the line as well as prevent drainage. If this is the case, clean or replace your AC filters.