AC Drain Line Overflows in the Attic

As warm indoor air passes over the cold evaporator coil, moisture condenses into water. On a humid monsoon day an AC can produce several gallons. That water drips into a pan under the coil and runs through a small PVC drain line, usually to the outside or to a plumbing drain.

Algae and slime grow inside the warm, damp line. Dust from the attic settles in the pan. Over months the line narrows and finally clogs. The primary pan fills and spills into a secondary pan beneath the unit, if there is one. If that pan is rusted, cracked or also full, water spills onto the attic insulation and ceiling drywall.

A float switch in the pan or drain line shuts the AC off when water rises. It is cheap and prevents most ceiling damage. Many older installations do not have one, or have one that no longer works. Ask your technician to install or test it.

A ceiling stain near the air handler or a return vent, water dripping from a vent, the AC shutting off unexpectedly, a musty smell when it runs and no water dripping from the outside drain line on a hot day are all signs. A dry outside line in summer often means the line is clogged upstream.

Have the drain line cleared at every spring service. Between visits, pour a cup of white vinegar into the access port near the indoor unit every month or two during cooling season. Keep the area around a closet air handler clear so leaks are easy to see.

Some homes have the air handler in a hallway or garage closet. Overflows there soak the closet floor, baseboards and the walls of nearby rooms. The same drain line care applies.

Turn the AC off at the thermostat. Put buckets under drips and, if the ceiling bulges, poke a small hole at the lowest point over a bucket. Call an HVAC company to clear the line and a restoration company to dry the ceiling; see AC condensate leak damage.

Phoenix attics can exceed 140 degrees in summer. Do not spend long in the attic yourself, carry water, and only step on joists or walkboards.

A slow overflow that keeps attic insulation damp for weeks can grow mold you smell through the vents. Wet insulation is usually removed and replaced after drying.

Some North Phoenix homes have a rooftop package unit instead of an attic air handler. Its condensate drains onto the roof or into a gutter. A clogged line can pond water on the roof and leak through the opening around the unit. The same spring cleaning applies.

When a line drips over weeks instead of overflowing all at once, insulation stays damp and mold can grow on the back of the drywall. A musty smell when the AC starts is a warning sign.

For the line, call an HVAC company. For a wet ceiling, call (602) 878-5475 for a local restoration provider who can start drying the same day.

A spring service, a float switch and a cup of vinegar a month cost a small fraction of drying and replacing a ceiling. Many HVAC companies offer maintenance plans that include drain line cleaning twice a year.

The technician clears the line with a vacuum or compressed air, flushes it, checks both pans for rust and cracks, tests the float switch and confirms water runs freely to the outside or drain.

Tell your landlord at the first sign of water near the AC. AC upkeep is usually the owner's job.

A cup of vinegar and a float switch protect your ceiling better than any repair after the fact. Clear the line every spring and check that water is dripping outside on hot days.

Book a spring AC service and ask for a float switch.

If you are unsure where your drain line exits, ask the technician to show you at the next service.

Clear the AC drain line every spring, add a float switch and pour vinegar into the line in summer. Those small steps keep the water in the pan and out of your ceiling.

Questions about ac drain line overflows in the attic? Call (602) 878-5475 to reach a local North Phoenix provider, 24 hours a day.