Double-Trapped Drain and a Float Switch Mistake: Think Physics First

In this Short, we walk through a real field miss on a complex, two-system install. Something under the unit shifted and created a double trap in the drain line, and because the float switch wasn’t wired to cut off both systems, one kept running. The fix was wiring the systems in series so a single switch shuts everything down, something that could have been done at install by running a control wire from the closet through the attic.

Nobody got in trouble over this mistake, but pain is an excellent teacher, and the goal is to learn the lesson without the pain. When an install is new or unusual, slow down and think through the physics: how will the water flow, and how is everything wired together? Physics works the same in an air handler, a condenser, or a condensate line.

The best way to be sure is to check one more time. Make that last check your first priority before you leave the job.