Once a year you should flush the traps on the drain pipes from your primary drain pans in your central air units. If you don't and the traps should become clogged, the water in the primary pan could overflow into the air plenum and collect onto the ceiling after missing the secondary pan.

Now I have a water spot on the ceiling to deal with.

The newer ACs do not have that problem. Haven't done it in over ten years.

Pour bleach down your drains before you run your A/C, let is sit for while in the trap usually will take care of the issues. Also will clean if your connection if it ties under the sink as well.

Once it starts heating up there are a lot of condensation lines that get backed up.

Several years ago I added simple clean outs just before the traps by adding a T-section of pipe with a short riser. An unglued cap is put on the top of the riser to keep out dust and trash.

I was just lazy and didn't get around to flushing the traps with little bleach and water as I usually do once the warm weather sets in.

How do these newer units drain the moisture that collects in the system? Don't all AC units pull and collect moisture out of the air?

Newer units have same issue, I see overflow tubes hanging from the eaves dripping rust color water every year in Frisco

I haven't been in my attic for over 10 years. I had to go up there every year before I replaced my old unit.

Perhaps installers no longer put traps on the drain pipes to avoid the clogging problem. Not sure there's enough sewer gas to cause a problem without them.

Good time to also inspect and clean your evaporator coils as well. Can also look at the internal catch pan under the coils to verify that it's relatively clean with no obstructions to the drain line(s) to keep things flowing freely.

Eventually, all condensate drains need attention. The HVAC industry has made major design improvements. Many of the new nonmetallic drain pans have an antibacterial product in the composition. But no engineer can change the law of physics and biology.

It is not IF the drain becomes blocked, it is WHEN. Also, the blockage can be at the unit but also at the drain termination point.

P Traps still required

I decked my attic a few years ago, I added about 1000 sq ft in storage room, for some reason my attic is about 15 feet high in the middle, I was thinking about making me an man cave up there

Had my units checked last week. The guy told me they don't recommend bleach anymore to flush; something about a chemical reaction that'll go back up the line and corrode the coil. Might be bs, but he said just boil water, let it cool for a couple of minutes and use it to flush.

Try these. Safer than bleach. I expect Lowes sell them or you can order something simular through the intra-net.

Pan Tablet?

Who A/C drains into a pan? Usually the pan is only used when the condensation line backs up.

Inside the cabinet of the evaporator there is a primary drain pan. This is where the primary drain line connects to indoor equipment. You can open the cabinet or coil box near the drain connection to access the primary pan.

If you are unable access primary pan readily, you can drop a couple of tablets into primary drain line instead of bleach. Sometimes you need to cut them in half.

The exterior pan you are referring to, is the secondary pan. This is pan that drips outside the home.

Sequence of drain events when unit is located in attic.
1. Primary drain
2. Secondary pan

Last but not lest ....ceiling.

Not if but when.

Adding tablets to electric air handler with a sde panel removed. Turn off power first!
If you have a gas furnace, it is a little more complex.

Thx for the reminder. Changed filter and poured bleach down drain tube