There is water standing under the indoor unit

Why it will not dry up

The water is made fresh on every cycle. What has changed is where it goes, and none of the three usual reasons clears itself.

A blocked drain line is the common one. Sludge builds at the trap over a season or two, the line backs up, and the pan overflows. The block does not wash through, because the flow that would clear it is the flow it is stopping.

A rusted-through drain pan on an older air handler leaks whatever the coil produces, clear line or not.

An iced coil thawing between cycles overruns the pan with more water than it was built to hold. A coil ices when airflow is short or the charge is low, so this one is a symptom of something else.

Where a float switch is fitted it shuts the system down rather than let the pan flood, which is why some people meet this as "the cooling stopped" rather than as water.

What the visit involves

A technician clears the line from the trap outward and checks the primary pan, the secondary pan and the float switch. Then comes the part that decides whether the water returns: why the coil was producing more than the drain could take. Filter, return, blower speed and refrigerant charge, with a temperature split measured across the coil.

What to say when you call

• Whether the water appears while the system runs, or after it stops
• Whether frost or ice has been seen on the indoor coil or the copper lines
• Whether the unit sits above a finished ceiling, in an attic, or in a basement
• Install year, your address and ZIP code

Common questions

Can the drain line simply be blown out? Sometimes, and on a straightforward clog that is the whole repair. Water that returns within days is the coil talking, not the drain.

The system shut itself off and there is water. Are those connected? Very likely. A float switch in the secondary pan cuts the call for cooling when the pan fills, which is exactly what it was fitted to do.

Why now, and not in June? The wetter the air, the more the coil has to drain. A partly blocked line copes in June and gives up in a July week with dew points near 66°F.