AC Frozen Evaporator Coil: Why Your Air Conditioner Ices Up in Humid SC Weather
AC Frozen Evaporator Coil: Why Your Air Conditioner Ices Up in Humid SC Weather A frozen evaporator coil occurs when the coil’s surface temperature drops below 32°F and moisture from your indoor air freezes on contact, building a layer of ice that blocks airflow and prevents heat absorption. The most common causes are restricted airflow from a clogged filter or dirty coil, low refrigerant charge from a leak, and blower motor failure that reduces air volume across the coil. In South Carolina’s high-humidity environment, frozen coils are both more common and more damaging than in drier climates — the heavy moisture content in Lowcountry and Midlands air means ice builds faster and produces more water when it melts. Coastal Carolina Comfort diagnoses and repairs frozen evaporator coils across Summerville, Charleston, Columbia, and all of South Carolina. Our NATE-certified technicians identify the root cause — not just thaw the ice — and provide upfront pricing before any repair begins. Call (843) 708-8735. How a Frozen Coil Damages Your AC System A frozen evaporator coil isn’t just a temporary inconvenience — it creates a cascade of problems that can damage multiple components if the system continues running. The compressor is at greatest risk. Under normal operation, liquid refrigerant enters the evaporator coil, absorbs heat, and exits as a gas before returning to the compressor. When the coil freezes, this heat exchange stops. Liquid refrigerant passes through the coil without vaporizing and reaches the compressor in liquid form. Compressors are designed to pump gas, not liquid. Liquid refrigerant entering the compressor — called liquid slugging — can crack valves, damage pistons, and cause catastrophic compressor failure. A compressor replacement typically costs $1,500–$3,000+. Water damage when the ice melts. A frozen coil accumulates a surprising amount of ice. When the system shuts off or the ice begins to melt, the resulting water can easily overwhelm the drain pan — especially if the drain line is also partially clogged (a common combination in South Carolina). Water overflows onto floors, into ceilings, or through walls. Read our guide on AC leaking water inside your house for immediate steps if you’re already dealing with water. Reduced system life. Repeated freeze-thaw cycles stress the coil fins, degrade the coil’s protective coating, and can eventually cause refrigerant leaks in the coil itself — one of the most expensive AC repairs. The 5 Causes of Frozen Evaporator Coils in South Carolina 1. Clogged Air Filter This is the most common cause — and the most preventable. A clogged filter restricts the volume of warm air passing over the evaporator coil. Without sufficient warm air, the coil’s temperature drops below the freezing point. Moisture in the air freezes on contact, and the ice layer further restricts airflow, accelerating the freeze. In South Carolina, where pet dander, pollen, dust, and high humidity all contribute to faster filter loading, a filter that might last 90 days in a drier climate may need replacement every 30 days during peak cooling season. The fix: Replace the filter, turn the system off for 2–3 hours to allow complete thawing, then restart. If the system runs normally and doesn’t refreeze, the filter was the sole cause. If ice returns within 24 hours, there’s an additional underlying issue. 2. Low Refrigerant From a Leak Low refrigerant charge causes the evaporator coil’s temperature to drop below normal operating range. When the coil is too cold, moisture freezes on its surface instead of condensing into liquid and draining away. The ice insulates the coil, making it even colder, and the freeze accelerates until the coil is completely encased. This is the most common mechanical cause of frozen coils, and it requires professional repair. A technician will thaw the coil, test for leaks, repair the leak source, and recharge the system to manufacturer specifications. Simply adding refrigerant without fixing the leak guarantees the problem will return. In South Carolina’s coastal environment, refrigerant line corrosion from salt air is a significant contributor to leaks — particularly on homes within a few miles of Charleston Harbor, James Island, or the Isle of Palms. 3. Dirty Evaporator Coil Even with regular filter changes, the evaporator coil accumulates dust, biological growth, and particulate matter over time — especially in South Carolina’s humid environment where mold and mildew thrive on the constantly damp coil surface. A dirty coil insulates itself from the warm air passing over it. The coil can’t absorb enough heat, its temperature drops, and the same freeze cycle begins. The difference is that a dirty-coil freeze develops more gradually than a low-refrigerant freeze — you might notice declining performance for weeks before ice becomes visible. The fix: Professional coil cleaning. This requires access to the indoor unit, coil-specific cleaning solution, and careful handling to avoid damaging the delicate aluminum fins. Coil cleaning is typically included in comprehensive maintenance visits that prevent frozen coils and costs $150–$300 as a standalone service. 4. Blower Motor Failure or Reduction The blower motor moves air across the evaporator coil. If it fails entirely, airflow stops completely and the coil freezes rapidly. A partially failing motor — running at reduced speed due to worn bearings, a failing capacitor, or a winding issue — moves insufficient air, causing a slower but equally damaging freeze. In multi-speed systems, a motor stuck on low speed may provide enough airflow for mild days but insufficient volume on high-demand days, creating intermittent freezing that’s harder to diagnose. 5. Collapsed or Blocked Return Ductwork If the return duct — the large duct that carries warm room air back to the air handler — is crushed, disconnected, or severely blocked, the volume of air reaching the evaporator coil drops below the minimum threshold. This can happen when stored items are placed on flex duct in an attic, when a duct joint separates due to age or poor installation, or when a return vent is blocked by furniture or closed. This cause is more common in homes with ductwork routed through attics — a standard