Every cooling season, the indoor coil in a split system or air handler pulls water out of the air. The condensate drain carries that water outside or to a floor drain. When the path stops flowing, water fills the drain pan under the coil. It either trips a float switch or spills over the edge and soaks the ceiling below. The shutoff is useful, but the stain is the part that costs money. A short walk now, before the heating season takes over the calendar, finds the problem while it is still small.
Find the trap and the pan
Start at the air handler with the power off at the disconnect. Confirm with a multimeter that the cabinet voltage is dead before you open the panel. Use a flashlight to look into the drain pan. Check for standing water, a film of algae, or sediment ridges along the bottom. Note whether the pan sits level. A tilted pan leaves water sitting in one corner even when the line itself is clear.
Next, follow the primary drain pipe from the pan outlet. Many indoor units route condensate through a trap, a U-shaped section that holds water so air cannot move through the line in the wrong direction. Check that the trap is full and that its depth matches the equipment instructions. A trap that has dried out or is too shallow can let air move through the drain path and slow the flow, so water sits in the pan longer than it should.
Clear it without making it worse
Pour a cup of clean water into the pan and watch the outside termination. If the water runs out steadily, the path is open. If it backs up at the pan, something is restricting it. A wet-dry vacuum on the exterior end can pull a clog out. Avoid stiff wire, which can crack a PVC joint or scrape a coil fin. For algae in the pan, use a cleaner the equipment maker approves, or ask your technician which product they use, and rinse thoroughly afterward.
Check the secondary drain or auxiliary pan too, if the home has one. Attic installations often include a second pan with its own line. Confirm that its outlet drips somewhere you can see it, such as near a window or over an exterior wall. An overflow that shows up outside is a nuisance. An overflow that shows up in the ceiling is a repair bill.
What the trade news says about the people you hire
ACHR News covers HVAC U's Building Analyst Professional certification, which the U.S. Department of Energy has recognized as Energy Skilled in the category of home upgrade advising. The HVAC U certification story describes the program as "designed for experienced home performance professionals" and points to energy modeling and building analysis as its focus. That is a whole-house energy credential. It does not tell you whether the person clearing your drain line has done that work, and it does not replace a direct answer about the job in front of you.
A separate ACHR News item on the PHCC's 2026 Connect conference describes more than 20 educational sessions and "opportunities for contractors to network with peers and industry experts" in its PHCC membership coverage. Attending training is a reasonable signal, but it is only a signal. Ask the contractor what they learned and how it changed the way they check drains, traps, and secondary pans on a service call.
Make the check a routine
A failing drain rarely announces itself until the ceiling shows a stain. That makes it easy to miss in a home where the owner is older or lives alone. Put a monthly glance at the pan, the drain outlet, and the ceiling below any attic unit on a calendar that someone actually reads. A family can arrange non-medical in-home support for older adults in St. Louis so that a regular visitor notices a wet spot or a unit that has shut off, then calls the family or the HVAC company. That person's job is to observe and call. Repairs stay with the technician.
Mark the date on the pan's edge with a marker after each clean, and photograph the outlet at the same spot each month. Bring those photos to the next service visit. A written history of clean, dry, and wet months gives the technician more to work with than a memory of when the water last showed up.