Carlo DeLuca, Master plumber As an Amazon Associate I earn from qualifying purchases. Some links are affiliate links.
The house sat for a week. No one ran the air. When the coil came back on, the closet pan filled overnight. The outdoor dump stayed dry. The primary line looked clear. The trap under the air handler held nothing.
A condensate trap is a small water seal. It keeps the blower from pulling air the wrong way through the drain. It also keeps the water moving in the right direction once the coil starts making condensate. Florida air handlers pull a lot of water. A dry trap does not establish that flow. The water sits in the pan instead of leaving the closet.
This is not algae. Algae turns a trap green and clogs the path. A dry trap is empty. You can see through the clear section or tip the assembly and nothing comes out. The unit ran. The pan held the water. The line never got the chance.
After-work check
Open the closet after the unit has been off. Look at the trap first. A clear P-trap or the low point of the PVC should hold a little water if the seal is intact. An empty trap after a quiet week is the whole story. Then look at the pan. A film of water or a wet ring means the coil made condensate and it had nowhere to go. The outdoor dump being dry only proves the water never reached it. Follow the white PVC from the coil to the wall. Confirm it still falls away. The closet guide shows the rest of the assembly: air-handler closet. After a heavy band the same backup can stain the ceiling below: after-storm.
Do not
Do not pour bleach or a cleaner down a dry trap and call it fixed. The seal has to be water. Do not cut the PVC and replace the whole run because the pan is wet. The line can be fine. The trap simply lost its seal while the house sat. Do not treat a full pan as a humidity problem first. The hallway can feel fine while the closet holds water that never left. Measure living-space relative humidity (RH) with Reed if the house still feels heavy after the pan is dry and the trap is primed: how to measure. Do not open a pressurized supply line to chase this. The water in the pan is condensate, not city water.
Run this
- Shut the unit. Empty the pan into a bucket. Confirm the line is empty before you power the coil again.
- Prime the trap. Pour a cup of water into the cleanout or the open end of the trap until you see a standing seal. A clear section makes this easy. If the trap is solid PVC, pour until water shows at the outdoor dump, then stop. The seal is what matters.
- Confirm the outdoor dump is clear and the secondary stub is open. Leave a leak puck in the dry pan so the phone knows next time. The overflow pan should text you before the ceiling does. See the overflow pan should text you.
A primed trap keeps the water moving once the coil starts. When the closet sits below the outdoor dump a pump still has to lift the water. The PumpSpy CP-120 is assembled in the USA and built to move the volume a Florida closet makes when the trap is doing its job.
FloridaDamp is an Amazon associate — we earn from qualifying purchases. I still point at this one because it is an assembled-USA condensate pump that will actually drain a closet pan, not because anyone paid for a review.
Prime the trap. Empty the pan. Keep the seal in place after a quiet week.
If it’s useful, it’s beautiful.
Carlo DeLuca is a third-generation master plumber writing from coastal Florida. Notes are educational. Not a service call.