I apologize in advance for this long post. This is the first summer in this home that I bought. I'm a first time homeowner. One day I realized a big stain in my ceiling right under the attic and found out that the drain pan was overflowing. Called the AC guy and he came and blew air into the clean out of the drain line as well as from the other end outside of the house. He also attached a sensor on the side of the drain pan.
We thought that had solved the issue. A few days later I go into the attic to check the roof since we are going to get the roof done soon. I noticed that the pan was pretty full but the sensor did nothing to tell me this. Decided to do some YouTubing and used a wet/dry vac to clean up the water in the pan as well as suck it out of the drain line. Basically every time we leave the AC on for a day or so the drain line fills back up all the way to the top where the clean out is. Then the AC unit starts to drip underneath. I'm not sure if it ever drips out from the clean out at all but it could be very likely. Every few days we have to vacuum this drain line. We even did the whole vinegar thing for 30min and then flushed it with warm water which came out clean.
Did some more research and learned about P-Traps and realized that I do not have one of these connected to my AC unit. The area in my attic is basically just a crawl space and very tight. From what I can see, there is just one pipe that goes underneath the whole unit then takes a 90 degree turn to the left wall.