May 30, 2025
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If you've ever walked past your AC and noticed ice forming on the coils or refrigerant lines—even during the Texas heat—you’re not alone. A frozen HVAC system is more than just a strange sight; it’s a red flag that something’s not working correctly. In this post, we’ll explain the top reasons why HVAC systems freeze up, what you can do about it, and when to call a professional.
When we say your AC is "freezing up," we’re talking about the evaporator coil or refrigerant lines forming ice. This happens when the temperature inside the system drops below freezing and condensation turns to ice. But for that to happen, something has to disrupt the system’s airflow, refrigerant balance, or heat absorption cycle.
This isn't just a minor glitch—it can severely damage your compressor or coil, which are among the most expensive parts to replace in an HVAC unit. If you see ice, shut the system off and investigate right away.
A dirty filter restricts airflow, making it difficult for warm air to pass over the evaporator coil. Without that warm air, the refrigerant inside the coil doesn't absorb heat properly—causing the coil’s temperature to drop and eventually freeze.
What to do: Replace filters every 30–90 days, especially during peak usage seasons.
Learn more about HVAC maintenance
Low refrigerant causes pressure drops in the system, which lowers the coil’s temperature and can easily lead to freezing. Leaks are common in aging systems or poorly installed units.
What to do: This requires a licensed HVAC technician. Look out for oily residue or hissing sounds near the coil—signs of a leak.
Dust, dirt, or mold buildup acts as insulation on the evaporator coil. This prevents proper heat absorption, causing the coil to get too cold and freeze.
What to do: Schedule professional coil cleaning during your seasonal tune-up.
Read about the benefits of air duct cleaning
Homeowners often close vents to redirect airflow, but this can actually reduce the total volume of warm air reaching the coil—leading to freezing.
What to do: Keep supply and return vents open and unobstructed. Avoid blocking them with furniture or rugs.
If your thermostat doesn’t shut off when it should—especially during cooler nights—the unit can run too long and freeze. A malfunctioning thermostat can keep your system working overtime when it’s not necessary.
What to do: Test or replace your thermostat and consider upgrading to a smart model.
Ask about thermostat installation options
Running your AC when outdoor temps are already low can trigger freezing since there’s not enough heat to absorb.
What to do: Avoid running your AC at night or when outdoor temps drop below 60°F.
A blocked drain causes water buildup around the coil. If airflow is also restricted, this water can freeze and spread to other components.
What to do: Check the drain pan and clear the drain line regularly.
Prevent issues with an annual maintenance agreement
Step 1: Turn off the system.
Switch the thermostat to "Off" to stop the freezing cycle and prevent further damage.
Step 2: Turn the fan to "On."
This circulates warm air over the coil and accelerates the thawing process.
Step 3: Do NOT chip away the ice.
Using sharp objects can puncture the coil or refrigerant line, leading to expensive repairs.
Step 4: Check the filter.
A clogged filter may be the root of the problem. Replace it before turning the system back on.
Step 5: Call a professional.
If the system refreezes or you suspect a refrigerant leak, it's time for a service call.
Book a professional inspection today
Regular maintenance is your best defense:
Joining a maintenance agreement ensures a professional checks your system twice a year, minimizing the risk of freeze-ups and maximizing performance year-round.
If your evaporator coil continues to freeze—even after cleaning and repairs—it may be a sign of larger issues, like a failing blower motor, undersized ductwork, or aging system components. In that case, you’ll want to talk to an expert about your options.
A frozen AC isn't just uncomfortable—it’s dangerous for your HVAC system. By understanding the causes and knowing what to look for, you can take quick action and prevent expensive breakdowns.
If you're dealing with a frozen system or want to avoid it in the future, the team at Air Techs Heating & Cooling is ready to help. From emergency repairs to preventative maintenance, we keep your home cool and worry-free.
Call now or schedule your appointment online to get your system back on track.
