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
Why Is My AC Running But Not Cooling the House?
Why Is My AC Running But Not Cooling the House? When your AC runs continuously but your home isn’t reaching the set temperature, the system is either failing to produce adequate cooling or losing that cooling before it reaches your living spaces. The most common causes are low refrigerant charge from a leak, a dirty evaporator or condenser coil restricting heat transfer, leaking ductwork that dumps conditioned air into unconditioned spaces, or a system that is undersized for your home’s actual cooling load. Coastal Carolina Comfort diagnoses why your AC isn’t cooling effectively across Summerville, Charleston, Columbia, and every community we serve in the South Carolina Lowcountry and Midlands. Our NATE-certified technicians identify the root cause — not just the symptom — and provide upfront pricing before any repair begins. Call (843) 708-8735. First: Understanding the Difference Between “Not Cooling” and “Blowing Warm Air” These two problems overlap but aren’t identical, and the distinction affects the diagnostic path. AC blowing warm air means the air from your vents is noticeably warm — room temperature or warmer. This typically points to a complete failure of the cooling cycle: dead compressor, severely depleted refrigerant, tripped outdoor breaker, or a heat pump stuck in heating mode. If this describes your situation, our guide on AC blowing warm air covers those specific causes. AC running but not cooling means the system produces some cool air — you can feel it at the vent — but your home never reaches the set temperature, or takes far too long to get there. The system runs for hours without cycling off. This is a subtler problem with a wider range of possible causes, and it’s what this article addresses. In South Carolina’s climate, the distinction matters more than in cooler regions. A system that’s “almost cooling” but falls 5°F short can leave your home at 80°F with 70% humidity — which feels miserable even though the AC is technically doing something. The 7 Most Common Reasons Your AC Runs But Doesn’t Cool 1. Dirty Condenser Coil (Outdoor Unit) The condenser coil is where your system releases the heat it absorbed from inside your home. When the coil’s aluminum fins become coated with dirt, pollen, grass clippings, or pet hair, heat transfer drops dramatically. Your system still runs — the compressor works, the fan spins, cool air reaches the vents — but the system can’t reject enough heat to keep up with the load. In South Carolina, condenser coils take a beating. Spring pollen coats them heavily by April. Summer storms blow debris into the fins. And the combination of heat and humidity creates ideal conditions for biological growth between the fins. This is one of the most common — and most fixable — reasons an AC runs all day without cooling adequately. A professional coil cleaning restores heat transfer capacity and is typically included in regular maintenance that prevents costly repairs. 2. Dirty or Restricted Evaporator Coil (Indoor Unit) The evaporator coil absorbs heat from your indoor air. When it becomes coated with dust, mold, or biological growth — which happens faster in South Carolina’s humidity than in drier climates — its ability to absorb heat decreases. The air passing over a dirty evaporator coil cools less effectively, which means the air reaching your vents is cooler than room temperature but not cold enough to overcome the heat gain in your home. A dirty evaporator coil also increases humidity in your home because the coil can’t properly dehumidify the air passing over it. This is why a home might be at 74°F but feel clammy and uncomfortable — the AC is partially cooling but failing to adequately remove moisture. Learn more about what South Carolina humidity does to your cooling system. 3. Low Refrigerant Charge A partially depleted refrigerant charge produces exactly this symptom — the system runs, cool air reaches the vents, but the cooling capacity isn’t enough to match the heat load. Unlike a completely empty system (which blows warm air), a slow leak creates a gradual decline in performance that homeowners often attribute to “the system getting old” or “it’s just really hot outside.” The temperature differential between the supply air and return air tells the story. A properly charged system in South Carolina should produce a 15–20°F differential. If your supply air is only 8–12°F cooler than your return air, low refrigerant is a prime suspect. 4. Ductwork Leaks This is the hidden culprit that no amount of AC repair will fix, because the AC itself is working correctly. If your ductwork has gaps, disconnected joints, or deteriorated flex connections — especially where it runs through an unconditioned attic — cooled air escapes before it reaches your rooms. In a Lowcountry attic during summer, ambient temperatures regularly exceed 140°F. A duct leak in that environment doesn’t just lose cooled air — it actively pulls superheated attic air into the duct system, warming the conditioned air as it travels to your vents. Ductwork problems are especially common in older homes across Summerville’s Historic District, Charleston’s peninsula, and Columbia’s Shandon and Forest Acres neighborhoods where original ductwork may be 30–50+ years old. 5. Undersized or Improperly Sized System If your AC system was sized incorrectly for your home’s actual cooling load, it will run continuously on hot days without ever reaching the set temperature. This is more common than you’d expect, particularly in South Carolina where cooling loads are exceptionally high. An undersized system literally cannot produce enough cooling capacity to overcome the heat gain from walls, windows, attic, and South Carolina’s relentless humidity. Oversized systems create a different problem — short cycling — but undersized systems simply run all day, every day, wearing themselves out faster and costing more to operate. Sizing problems are especially prevalent in new construction where builder-grade systems may have been selected for cost rather than performance, and in homes that have been renovated or had additions built without upgrading the HVAC system to match the increased square footage.
AC Blowing Warm Air? What South Carolina Homeowners Should Check First
AC Blowing Warm Air? What South Carolina Homeowners Should Check First An AC system blowing warm air is most commonly caused by low refrigerant from a leak, a failed or failing compressor, a thermostat set incorrectly, or a frozen evaporator coil that has thawed and re-frozen in a cycle that prevents proper cooling. In South Carolina’s climate — where indoor temperatures can climb past 85°F within hours of losing cooling — identifying the cause quickly matters both for comfort and for preventing secondary damage to your system. Coastal Carolina Comfort’s NATE-certified technicians diagnose the root cause of warm air from AC vents across Summerville, Charleston, Columbia, and the entire South Carolina Lowcountry and Midlands. Most warm-air issues can be diagnosed and repaired in a single same-day visit. Call (843) 708-8735 to schedule your diagnostic. Quick Checks Before You Call a Technician Before scheduling a service call, run through these homeowner-safe checks. They take less than five minutes and resolve the problem roughly 15% of the time. Check your thermostat settings. It sounds basic, but it’s the first thing our technicians verify on every call. Make sure the thermostat is set to “cool” (not “heat” or “fan only”) and that the set temperature is at least 3–5°F below the current room temperature. If someone in the household accidentally bumped the setting — or if a smart thermostat entered a scheduling mode — the system may be functioning exactly as programmed, just not as you expected. Check the air filter. A severely clogged air filter restricts airflow across the evaporator coil. When airflow drops below the minimum threshold, the coil temperature plummets, moisture on the coil freezes, and ice builds up until the coil can no longer absorb heat from your indoor air. The result: your system runs, but the air coming from the vents is room temperature or warmer. Pull the filter out. If you can’t see light through it, replace it and give the system 2–3 hours to thaw before restarting. Check the outdoor unit. Walk outside and look at the condenser unit. Is the fan spinning? If the outdoor unit is completely silent or humming but the fan isn’t moving, the system can’t release heat — which means it can’t cool your home. A non-spinning fan usually points to a failed capacitor or burned-out fan motor. Do not attempt to manually spin the fan blade — call for professional repair. Check the circuit breakers. Your AC system typically runs on two breakers — one for the indoor air handler and one for the outdoor condenser. If the outdoor breaker has tripped but the indoor breaker hasn’t, the air handler will continue to blow air through your vents, but without the outdoor unit running, that air won’t be cooled. Reset the breaker once. If it trips again immediately, stop — that indicates an electrical fault that requires professional diagnosis. If none of these checks resolve the issue, the problem is internal to the system and requires a trained technician. The 6 Most Common Causes of an AC Blowing Warm Air 1. Low Refrigerant From a Leak This is the most frequent cause of warm air from AC vents in South Carolina. Your air conditioning system doesn’t consume refrigerant — it circulates the same charge in a sealed loop. If the charge is low, there’s a leak somewhere in the system. Low refrigerant reduces the evaporator coil’s ability to absorb heat from your indoor air. As the charge drops, the temperature differential between supply air and return air narrows until the air coming from your vents feels lukewarm or warm. In South Carolina’s high-humidity environment, low refrigerant also causes the evaporator coil to operate below the dew point in unpredictable ways, leading to inconsistent cooling and excessive condensation or ice formation. Coastal Carolina Comfort performs a leak check, locates the source, repairs it, and recharges the system to manufacturer specifications. Simply adding refrigerant without finding the leak is a temporary fix that will fail again — often within weeks in the Lowcountry’s demanding climate. Learn more about what South Carolina’s climate does to your cooling system. 2. Compressor Failure The compressor is the component that pressurizes refrigerant and drives the entire cooling cycle. When it fails — partially or completely — the system loses its ability to transfer heat from inside your home to the outside. Your air handler will still blow air through the vents, but that air won’t be cooled. Compressor failures in South Carolina are often caused by extended run times during sustained summer heat, chronic low refrigerant that forces the compressor to work harder, electrical issues from power surges, or simple age-related wear. The outdoor unit may hum without starting, make a clicking sound as it tries repeatedly to engage, or trip the circuit breaker. Compressor replacement is one of the most expensive AC repairs — typically $1,500–$3,000+ depending on the system. For systems over 10 years old, this repair often triggers a conversation about whether to repair or replace your AC system. 3. Frozen Evaporator Coil A frozen evaporator coil can’t absorb heat. When ice builds up on the coil, airflow drops further, the ice gets worse, and your system enters a downward spiral where it runs constantly but cools poorly or not at all. The most common causes are restricted airflow (clogged filter, closed vents, dirty coil) and low refrigerant. In South Carolina’s humid climate, frozen coils are particularly problematic because the ice melts and refreezes in cycles that can flood your condensate pan and overflow onto floors. Read our full guide on frozen evaporator coils in humid South Carolina weather. 4. Thermostat Malfunction A thermostat that reads the wrong temperature, loses its connection to the system, or has a dead battery in a wireless sensor can cause the AC to behave erratically — including blowing air without activating the cooling cycle. Modern smart thermostats with multiple sensors, scheduling features, and Wi-Fi connectivity have more potential failure points than older mechanical models. If your