Top-rated independent heating and cooling across north Georgia and the southern Appalachians
A Frozen AC Coil and What Causes the Ice
You go to change the filter and there is a block of ice on the indoor coil, or the outdoor line is wearing a frost sweater and the house never gets cool. A frozen coil is a symptom, not the disease. We repair frozen coils and the airflow and refrigerant problems behind them across Alabama, Georgia, Kentucky, North Carolina, South Carolina and Tennessee. Turn the cooling off, leave the fan on, and call us.
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STM Heating & Air service team · field-reviewed before publishing
What Ice on the Coil Is Actually Telling You
The indoor coil gets cold by boiling refrigerant inside it. Warm room air blowing across that coil keeps the surface above freezing. Take away enough of that warm air, or drop the pressure inside the coil too low, and the surface falls below 32 degrees. Moisture in your air condenses and freezes instead of draining. Once ice forms it blocks even more air, so the freeze feeds itself and spreads down the line to the outdoor unit. That is why the house gets warmer while the system runs harder. Running an iced system pushes liquid refrigerant back toward the compressor, which is the expensive part. Shut the cooling off first, then diagnose.
Cause One: Airflow, and It Usually Is
Most frozen coils we open up are airflow problems, and most airflow problems are cheap. A filter loaded with red clay dust and pet hair is the number one offender in our region. After that, closed or blocked supply vents, a crushed or disconnected flex duct in a crawlspace, and returns choked by furniture. Then the coil itself: years of dust bonded to the fins makes a felt mat that air will not pass through. Blower issues come next, a failing capacitor or a motor running at the wrong speed. None of these need refrigerant work. Many are a filter, a vent, and a coil cleaning.
Cause Two: Refrigerant Charge, Cause Three: Controls
If airflow checks out, the charge is next. Low refrigerant means the system is leaking, since it does not get used up. Low charge drops the pressure in the coil and the boiling temperature goes below freezing. That is a leak search and a repair, not a top-off, because a system we just refill will freeze again next summer. Controls make up the rest: a thermostat set to run the system nonstop on a mild, damp night, a stuck contactor, a bad metering device, or a heat pump reversing valve that will not fully shift. Cool 60 degree nights in the foothills with the AC running can frost a coil on their own.
What You Can Safely Check Yourself
Turn the thermostat cooling off and set the fan to ON. That pushes room air over the coil and thaws it, usually in a few hours. Put a towel under the indoor unit, because thawing ice becomes water. While it melts, change the filter, walk the house and open every supply and return vent, and pull leaves, grass clippings and mulch back from the outdoor unit. Check the breaker and the thermostat batteries. That is the safe list. Do not chip at the ice, do not put a heat gun or hair dryer on the coil, and do not open refrigerant lines or panels with line voltage behind them.
What a Technician Does Differently
We measure instead of guess. Static pressure across the blower tells us whether the duct system is strangling the equipment or whether the coil is dirty. Temperature split across the coil, superheat and subcooling readings, and amp draw on the blower motor separate an airflow problem from a charge problem in the first fifteen minutes. If the charge is low we look for the leak with electronic detection or nitrogen pressure, then quote the repair honestly, including when the coil is old enough that replacement makes more sense. We also check the condensate drain, because a coil that froze once has probably been dumping more water than the pan expected.
When it is time to book
A Frozen AC Coil and What Causes the Ice — fast answers
How long does it take a frozen coil to thaw?
With the cooling off and the fan set to ON, most coils clear in two to four hours. A heavy block of ice can take overnight. Put a towel or shallow pan under the indoor unit for the meltwater.
Can I just run the AC and let the ice melt on its own?
No. Running the cooling with ice on the coil sends liquid refrigerant toward the compressor and can destroy it. Turn cooling off at the thermostat, leave the fan running, and let it thaw before anyone tests the system.
Will a new filter fix it for good?
Sometimes, if a clogged filter caused it. If the coil freezes again within a few weeks with a clean filter, something else is wrong, usually duct restriction, a dirty coil, a weak blower or a refrigerant leak. Call us for air conditioning repair.
How it works
- Step 1
Tell us the symptom
Call or fill in the quote form and describe what you hear, smell or feel. Warm air, short cycling, a breaker that keeps tripping. That gives us a head start on the likely cause.
- Step 2
We diagnose on site
A technician checks the thermostat, airflow, electrical connections, refrigerant performance and the outdoor unit. We work the crawlspace and the attic too, because ductwork and drainage cause more trouble than people expect.
- Step 3
You decide, then we fix it
We explain what failed, what it takes to repair it, and what we would watch next season. No work starts until you say go. Most repairs finish the same visit when parts are on the truck.
- A real person answers
- Open 7 days
- Written quote before work starts
Why homeowners call us
- Mixed heating is normal to usHeat pumps, propane furnaces and dual-fuel setups all behave differently in cold weather. We know how a heat pump should sound in the thirties and when the backup heat is doing too much of the work.
- We go under the houseRed clay crawlspaces hide crushed ducts, sweating lines and standing water. Comfort problems often start down there, not at the unit, so we look before we start replacing parts you may not need.
- Plain explanationsYou get told what broke and why, in words that make sense. If a repair is a short-term patch on an aging system, we say that out loud so you can plan instead of guessing.
- One crew, six statesWe serve homeowners across Alabama, Georgia, Kentucky, North Carolina, South Carolina and Tennessee. Same approach in every one: show up, diagnose properly, repair what needs repairing, leave the space clean.
- All major brands, gas & electricOne independent crew for Carrier, Trane, Lennox, Goodman, Rheem and more.
- Straight answersNot worth fixing? We say that out loud, and often it saves you the visit fee.
About this guide
Safe checks done and it still misbehaves? That's a real fault
Bring your notes from the checks to the call and booking takes no time.
- A real person answers
- Open 7 days
- Written quotes
- All major brands
- Gas & electric
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