Why Is Water Leaking Around My Indoor Unit?

Do this first

• Turn cooling off at the thermostat so the system stops making condensate
• Soak up standing water so it does not reach drywall, flooring or a ceiling below
• Look for the float switch — many systems have one that should have cut power before the pan overflowed, and a pan that overflowed anyway means that switch failed or is missing

Why the line blocks

The drain line carries cool, damp, still water, which is a good environment for algae and biological growth. Add attic dust and it plugs. This is the single most common summer service call there is, and it is almost entirely preventable.

The other causes

• A frozen coil that has thawed, dumping more water than the pan can take at once
• A rusted or cracked drain pan on an older system
• A condensate pump that has failed, on installations where the drain has to be pumped uphill
• Poor attic installation where the unit is not level, so the pan drains toward a corner with no outlet

Keeping it from happening again

Clearing and treating the condensate drain is part of a maintenance visit. That is a large part of why an $88 tune-up before the season is worth more than it costs — this failure damages ceilings, and the drywall usually costs more than the HVAC repair.