AC Frozen Coil & Water Leaks

Ice on an AC’s indoor coil or copper lines, paired with water pooling near the unit, means one of two things: a frozen evaporator coil that is now melting, or a clogged condensate drain line overflowing on its own. Trusted Heating & Air Conditioning provides residential professional AC repair across North Texas, where most homes tuck the air handler into the attic and a long cooling season pushes far more condensate through the drain than milder climates see. Either problem can soak an attic floor or a ceiling fast, so the first move is the same either way: switch the thermostat to FAN or OFF and stop the compressor from running.

A frozen coil and a clogged drain look the same but are different problems

Both show up as water where it shouldn’t be, but the mechanism is opposite. A frozen coil forms ice on the evaporator (the cold coil inside the air handler) or on the refrigerant lines, then drips or gushes water once the system shuts off and the ice melts. A clogged drain never freezes anything; the coil runs fine, but condensate backs up in the pan and overflows because the pipe carrying it away is blocked. Touch the copper line at the unit first. Ice or heavy frost means a freeze; a dry line with standing water in the pan points to a clog, covered below.

Why your evaporator coil freezes in the first place

An evaporator coil freezes when it runs colder than it should for longer than it should. A dirty air filter or blocked return grille starves the coil of warm airflow, so refrigerant inside stays too cold and frost builds instead of condensation draining off. Low refrigerant charge from a slow leak behaves differently: airflow is fine, but there isn’t enough refrigerant to carry heat away, so pressure drops and ice forms even with a clean filter. North Texas systems run for months without a real break, so a marginal filter or a small leak that a milder climate might tolerate for years shows up here in a single summer.

How to thaw a frozen AC coil safely

Turn the thermostat to FAN ONLY or OFF, and leave the outdoor condenser powered off too if it has a separate switch. Do not run cooling again until every trace of ice is gone; restarting on a partially frozen coil just refreezes it. Full thaw usually takes two to four hours, longer for a heavily iced coil, and running the indoor blower on FAN speeds it up. Put towels and a shallow pan under the air handler first, since a fully iced coil releases a surprising amount of water at once. Once it’s clear, check and replace the filter if it’s dirty, the most common cause and the cheapest to rule out.

What not to do while it thaws

Do not chip, pick, or scrape ice off the coil with a tool. The fins are thin aluminum and bend or puncture easily, and a punctured coil is a refrigerant leak you just created. Do not use a hair dryer or space heater near it; an electrical heat source close to sealed components is its own hazard. Do not keep restarting the system to “check if it’s working” before it’s fully thawed. A coil that refreezes within a day or two of a fresh filter is a sign of a refrigerant leak, covered below, and calls for a licensed technician rather than another thaw-and-restart cycle.

The clogged condensate drain line causes most attic water leaks in North Texas

A central AC pulls moisture out of the air simply by cooling it, and that water runs down a PVC drain line to an exterior or floor drain. Algae, dust, and debris build a biofilm inside that line over a cooling season, and DFW’s long run-time pushes more volume through it than a shorter season would. Once the line clogs, condensate backs up into the pan under the attic air handler and has nowhere to go but over the edge, onto the attic floor or through the ceiling below. This is the most common water-damage call Trusted Heating & Air sees on attic-mounted systems across Collin County and Plano, and it’s a plumbing blockage created by run-time and debris, not humidity or mold in the air the system is cooling.

Why your float switch shut the system off (and how to check it)

Most attic air handlers installed in the last decade or two include a float switch, a small safety device that cuts power the moment water rises past a set level. An AC that simply stopped cooling with no ice on the lines likely tripped its float switch, and that switch did its job: it kept a clog from becoming a ceiling collapse. Find it clipped to the drain pan or inline on the PVC pipe, and check for standing water in the pan. Standing water means the drain is blocked downstream, and clearing the switch without clearing the line just lets the pan refill in a day. Shut off power at the breaker before touching anything near standing water and electrical components.

A musty smell from the vents usually means biofilm in the drain pan

Standing condensate that never fully drains grows a thin biofilm, the same slippery buildup found in a birdbath left too long, and running air across it pushes a musty odor through the ducts. This is a drain-and-pan cleaning issue, not a mold-remediation situation, and it typically clears once the line is flushed and the pan is wiped out. A wet-dry vacuum at the exterior drain outlet pulls most clogs out in one pass. A cup of distilled white vinegar poured into the drain line’s cleanout tee, left thirty minutes, then flushed with water, breaks down the remaining biofilm without harsh chemicals.

When ice or water points to a refrigerant leak

If the coil keeps freezing after a fresh filter and a clear drain, refrigerant charge is the next thing to check, and this is where DIY stops. Recharging a leaking system without finding and sealing the leak only buys a few weeks before the ice returns, because refrigerant that leaked out is gone, not used up. As of 2026, R-410A systems already installed remain fully legal to service, recharge, and repair; the January 2025 change was a manufacturing cutoff that stopped new equipment from shipping with R-410A, not a ban on servicing what’s already running in North Texas attics. A bidder who says your R-410A system “can’t be recharged anymore” or is somehow illegal is a bidder worth a second opinion. Trusted Heating & Air’s EPA Section 608 certified technicians locate the leak with an electronic detector, seal it, then recharge to spec, the only version of this repair that holds.

How to prevent the next attic overflow

A twice-yearly drain flush, spring and mid-summer, keeps biofilm from building to a clog, and it takes fifteen minutes with a wet-dry vacuum at the exterior outlet. Filter changes on a 30-to-90-day cadence (tighter for pets or a dusty attic) prevent the airflow-starvation freeze behind most frozen-coil calls. A secondary drain pan with its own separate line, standard on many installs but worth confirming on an older one, catches an overflow before it reaches the ceiling even if the primary line clogs again. Confirming the float switch is present and wired correctly is a five-minute check worth asking for at any maintenance visit.

When to DIY and when to call a licensed pro

Filter checks, a visual look at the drain pan, a wet-dry vacuum flush at the exterior line, and resetting a float switch after confirming the pan is dry are safe for a homeowner to handle. Refrigerant work, opening the sealed system, and anything near standing water and live electrical connections belong to a licensed technician, full stop. So does a coil that refreezes repeatedly despite a clean filter and clear drain; that’s a leak or component failure, not a maintenance gap, and repeated thaw-and-restart just delays a pricier repair. A unit needing a coil thaw or drain clear more than once a season, more than its age alone, is the real signal to have Trusted Heating & Air’s licensed technicians (TDLR #TACLA152199C, active through June 2027) diagnose the root cause first.

Standing water near an attic air handler or a coil that won’t stay thawed is worth a same-day call rather than a wait-and-see. Trusted Heating & Air Conditioning is owner-operated, BBB A+ accredited, and offers 24/7 same-day service across Collin County and Plano. Call (945) 333-4822 to get the drain cleared, the leak found, or the coil diagnosed before it happens again.

Ready to fix it right? schedule your AC repair or call (945) 333-4822.