While I can't see it from here, I'll throw a couple of ideas out there: 1. clogged drain pan/pipe 2. Have you changed your filter (if there is one)?

Find the drain line and if there is no union to take apart cut it be careful and understand that you may get wet if you have water there then it is plugged up downstream from you blow out the line with compressed air, if it is dry there then the plug is close to the coil if you blow it back then the plug will just return later no matter what you need to clean the pan make sure all the drains lines are clear and you might as well clean the coil while you are this far into it and make sure you have a clean filter

Here is a link that might be useful: Air Conditioning Repair made Easy