Why Are My AC Coils Frozen in San Marcos?

Why Are My AC Coils Frozen in San Marcos?

Few HVAC problems are more frustrating than finding your air conditioner coated in ice on a hot San Marcos day. If you’ve noticed your system blowing warm air, running continuously, or leaking water near the indoor unit, there’s a strong chance that your evaporator coil has frozen. In such cases, it’s important to contact a trusted air conditioning service in San Marcos, TX to diagnose and resolve the issue promptly.

Frozen AC coils are more than just an inconvenience, they signal that something’s gone seriously wrong with airflow, refrigerant levels, or thermostat control. Left unchecked, this issue can lead to water damage, rising energy bills, and long-term system failure.

In this guide, we’ll explain the science behind frozen coils, explore the most common causes, and walk you through both homeowner-friendly solutions and professional repair options. Whether you’re in Willow Creek, Hughson Heights, or Blanco Gardens, this is what you need to know before your AC problems escalate.

What Are Frozen Coils and Why Should You Worry?

Your AC’s evaporator coil is a key component that absorbs indoor heat and transfers it outside. When it functions properly, your system cools efficiently. However, when airflow is reduced or the refrigerant level is low, the evaporator coil can drop below freezing. The moisture in the air turns to ice, creating AC ice buildup on the coil surface.

This ice restricts airflow further and reduces heat transfer, forcing your AC to work harder for less cooling. Left unaddressed, it can damage the compressor, blower motor, and control board, resulting in significant system failures and expensive repairs.

Real Complaints from San Marcos Homeowners

At Woods Comfort Systems, we’ve responded to countless service calls across San Marcos where frozen evaporator coils turned out to be just the beginning of more serious HVAC problems. Here are a few real scenarios:

• Willow Creek Estates: A homeowner reported their AC was blowing warm air on a 100°F afternoon. Upon inspection, the evaporator coil was found to be frozen solid due to a severely clogged return air filter.
• Heron Creek: A customer noticed water pooling around their indoor unit. Our team discovered that the ice buildup had melted overnight and overflowed the drain pan, which was caused by low refrigerant pressure.
• Hughson Heights: A newly renovated home started experiencing weak airflow and high humidity. The issue? Poor airflow, several closed supply vents, and an obstructed return caused airflow imbalance, leading to coil freezing.
• Blanco Gardens: A rental property owner contacted us about an AC that wouldn’t cool below 80°F. The root cause was a failing blower motor that reduced air velocity across the coil, causing intermittent freezing.

These real-world cases demonstrate that frozen coils are rarely isolated—they often indicate hidden inefficiencies or maintenance issues that require immediate attention.

Core Causes of AC Coil Freezing (With Technical Insight)

Let’s see why your AC won’t Turn On in San Marcos if its coil is frozen: 

1. Air Filter Neglect: The Invisible Blockade

Your dirty filter is the first line of defense against dust, debris, and allergens. However, when it becomes clogged, it becomes a roadblock for airflow. Without enough warm air passing over the evaporator coil, the refrigerant inside the coil can’t absorb enough heat. The coil temperature drops below freezing, and condensation on the coil turns to ice.

2. Refrigerant Leaks: Pressure Drop, Temperature Crash

Refrigerants are responsible for absorbing heat from the indoor environment. If your system is leaking refrigerant—even slowly—it lowers the pressure inside the coil. Lower pressure equals lower temperature, and once that temperature falls below 32°F, ice begins to accumulate on the coil.

3. Blocked or Closed Vents: Starving the System of Air

Homeowners sometimes close supply vents in unused rooms to save energy, but this strategy can backfire. Reduced airflow leads to heat transfer imbalances. Likewise, return blocked vents by furniture or drapes cause suction pressure drops that trigger freezing conditions.

This includes checking for collapsed flex ducts, improperly closed dampers, and pressure imbalances between zones when HVAC airflow problems are restored to optimize system efficiency and coil temperature.

4. Failing Blower Motor: A Critical Weak Link

The blower motor powers airflow across the evaporator coil. Suppose it’s underperforming due to wear, capacitor failure, or electrical faults, and the air velocity drops. Reduced velocity equals reduced heat exchange, which rapidly causes icing.

The ac repair services in San Marcos test motor amperage draw, check for winding resistance, and inspect associated capacitors. We repair or replace motors as needed to restore full airflow capability.

5. Thermostat Miscommunication: Overcooling Trigger

A thermostat that fails to read room temperature accurately or signals the AC to run excessively can result in overcooling. Overcooled coils drop into the freeze zone, especially in humid conditions.

The expert thermostat checks sensor placement and ensures proper staging of the cooling cycle. In some cases, upgrading to a smart thermostat improves system balance.

6. Dirty Evaporator Coils: Insulation by Contamination

Even if the filter is clean, coils collect grime over time. Dust, pet hair, and moisture cling to the coil surface, forming a layer of insulation that protects the coil. That layer prevents heat absorption, causing uneven temperature distribution—one side freezes while the other overheats.

The experts use chemical coil cleaning using HVAC-safe agents. The cleaning is followed by airflow testing to ensure unrestricted heat exchange.

How Homeowners Can Safely Defrost a Frozen AC System

If you suspect coil freezing, act fast—but carefully. Here’s how to safely thaw your unit without risking further damage:

1. Turn off the AC system at the thermostat. This stops active cooling and halts further ice formation.
2. Set the fan to “ON.” The indoor fan will push warm household air over the frozen coil, speeding up the melting process.
3. Open every supply and return vent. Improved airflow helps accelerate defrosting.
4. Check for water leaks. As ice melts, be prepared for water runoff—towels or a drain pan beneath the unit can help.
5. Wait 2–6 hours. Depending on the thickness of the ice buildup, complete thawing may take some time.
6. Avoid scraping the ice manually. Never use sharp tools or heat sources, such as hair dryers—they can damage coil fins or rupture refrigerant lines.

If freezing recurs after restarting the system, it’s a sign of a deeper mechanical or refrigerant issue that requires expert diagnostics.

Proactive Strategies to Prevent Coil Freezing

Regular system maintenance and innovative airflow management go a long way in preventing coil freeze-ups. Here are our recommended prevention tips

Professional Prevention Tactics:

• Replace filters every 30–60 days during peak usage
• Schedule biannual tune-ups (pre-summer and pre-winter)
• Inspect ductwork annually for leaks or obstructions
• Ensure thermostat calibration and programming align with seasonal patterns
• Upgrade to variable-speed air handlers or smart thermostats for precise humidity and cycle control

Homeowner Best Practices:

• Avoid closing supply vents unnecessarily
• Keep furniture and drapes clear of return registers
• Monitor humidity levels with a hygrometer
• Respond quickly to signs of ice or airflow reduction

Proactive steps like these not only prevent frozen coils but also boost energy efficiency and protect your equipment investment if you know how to defrost safely.

Professional Defrosting and Repair: When to Call Woods Comfort Systems

If your system continues to freeze or shows signs of a deeper failure, it’s time for licensed HVAC intervention. Frozen coils rarely exist in isolation—they’re often symptomatic of system-wide imbalances.

When you reach out to Woods Comfort Systems, our process includes:

• Precision refrigerant charge testing
• Static pressure readings across ducts
• Evaporator coil and blower assembly inspection
• Motor and capacitor diagnostics
• Full airflow and cycle calibration

With decades of service in San Marcos and surrounding areas, our team combines local knowledge with industry-best technology to resolve freeze issues quickly and thoroughly.

Schedule Expert Help with Woods Comfort Systems

Don’t wait for a frozen coil to damage your system beyond repair. If your AC is blowing warm air, making strange noises, or freezing over, call in the pros.

Woods Comfort Systems is the leading HVAC and plumbing company serving San Marcos, Buda, and surrounding communities. From airflow diagnostics to full-system repairs, we’ll get your comfort back on track fast.

Call (512) 894-8793today to schedule your air conditioning service in San Marcos, TX.