An AC freezes up because the evaporator coil drops below 32°F and the moisture in the air ices over it — almost always from restricted airflow (a dirty filter is the number-one culprit) or low refrigerant from a leak. As backwards as it sounds, this happens most in the dead of a Texas summer, and the first move is to shut the system off and let it thaw before the ice damages the compressor.
If you found ice on your indoor unit or a frosted-over copper line outside, this is the page for you. Here's exactly what to do in the next five minutes, why a coil freezes when it's 100 degrees out, what's actually causing it, and how to keep it from happening again.
First — it's iced. Do this right now.
Before anything else, stop the ice and protect the compressor:
Why the urgency? Running the system with a frozen coil can slug liquid refrigerant back into the compressor — the single most expensive part in your system — and overheat it. A $200 problem turns into a $2,000 one in an afternoon.
Why a coil freezes when it's 100° outside
This is the part that makes no sense until you see it. Your evaporator coil is cold by design — refrigerant inside it runs around 40°F, and warm air from your house blows across it, dumping its heat and its humidity (that's the water that normally drips out your condensate drain). The system is a balance: enough warm airflow and the right amount of refrigerant keep the coil safely above freezing.
Here's the vicious cycle: once a little ice forms, it blocks even more airflow, which makes the coil colder, which makes more ice. That's how you go from a thin frost to a solid block in a few hours. The 100-degree day outside has nothing to do with it — the problem is the temperature at the coil.
What's actually causing it
Run down this list roughly in order of how often it's the answer:
- A dirty air filter — the number-one cause, every time. A clogged filter starves the coil of the warm airflow that keeps it above freezing. DIY
- A dirty evaporator coil — dust films the coil and insulates it, dropping its surface temperature. Pro
- Closed or blocked vents and returns — furniture over a return, too many supply vents shut. Same effect as a dirty filter: not enough air. DIY
- A weak or failing blower motor — if the fan can't move enough air, the coil ices even with a clean filter. Pro
- Low refrigerant from a leak — low charge drops the coil's pressure and temperature below freezing. The fix is the leak, not a top-off (more below). Pro
- A clogged condensate drain — water backs up around the coil and freezes. DIY-ish
- Running it too cold overnight — set very low when the night load is light, a marginal system can dip below freezing. DIY
Notice the pattern: the top four are all airflow. That's why "change the filter" is the first and best thing you can do — it solves more freeze-ups than anything else, and it's a $12 fix.
The one that isn't a quick fix: low refrigerant
If your coil keeps freezing after you've handled the filter and the vents, the likely culprit is low refrigerant — and here's the part most companies won't tell you straight: refrigerant doesn't get used up. It's a sealed loop. If you're low, you have a leak. Topping it off buys you a few cool weeks before it fades and freezes again — that's a subscription, not a repair.
We don't recharge a system without finding the leak first. When you're low, we locate it, show you where it is, and quote the fix in writing. The deeper diagnostic version of all this — warm air, weak air, some rooms cold — is in our guide on an AC running but not cooling.
How to keep it from freezing again
- Change the filter every 1–3 months — monthly in peak Texas summer. This alone prevents most freeze-ups.
- Keep your vents and returns open — don't close rooms off to "save energy"; it just chokes the system.
- Get a yearly tune-up — a real one cleans the coil and checks the refrigerant charge before either can drop you below freezing.
- Don't crank it way down at night — give the coil a sane setpoint to work against.
When to call a pro — and what it costs
Call when it freezes again after a fresh filter, when you see ice on the copper lines, or when the air is warm even after a full thaw. Every visit starts with a flat $79 diagnostic and a written price. The common fixes here:
| Repair | What's included | Typical range |
|---|---|---|
| Service call & diagnosis | Full diagnosis + written quote (waived when you book) | $79 |
| Refrigerant & leak repair | We find the leak — no recharge-only | $200–$600 |
| Blower motor | OEM motor, airflow test | $400–$850 |
| Coil cleaning | Part of a full tune-up | From $99 |
Flat-rate, written, and approved before we start. For the full repair price list, see what AC repair costs in New Braunfels.
An iced-up AC means the coil fell below 32°F — almost always a dirty filter choking the airflow, or low refrigerant from a leak. Shut it off, run the fan to thaw it (1–3 hours), put towels down, and change the filter. If it freezes again, stop running it and call — and remember that "low on refrigerant" always means a leak to fix, not just more refrigerant.
Frozen up again in New Braunfels, Seguin, Canyon Lake, or anywhere nearby? We'll find why and quote it in writing. Call (830) 587-5790 or request a quote online.