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A Frozen AC Coil and What Causes the Ice
You open the return closet and there it is: a block of ice on the indoor coil, water on the floor, and warm air coming out of the vents. Your AC is running hard and cooling nothing. Ice on the coil is a symptom, not the disease. Turn the system off, set the fan to on, and read on before you call us.
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Written by the James River Heating & Air service team and checked by our field technicians
What ice on the coil actually means
A frozen evaporator coil means the coil got colder than it should and moisture in the air froze on it instead of draining away. Once ice forms, it blocks airflow, which makes the coil colder still, so the problem snowballs within an hour or two. The two root causes are almost always airflow that dropped or refrigerant charge that dropped. Both look identical from the hallway. Running the system while it is iced can flood the pan, soak insulation and, in the worst case, push liquid refrigerant back to the compressor. Shut cooling off first, then diagnose.
Cause one: airflow, and it is usually the filter
Start with the cheapest and most common cause. A loaded filter starves the coil, and in our humid summers a one inch filter can go from clean to packed in a few weeks. Closed or blocked supply vents do the same thing, as does furniture over a return. In houses across the region with ducts in vented crawlspaces, we also find crushed flex duct, disconnected boots and a return that has pulled loose, all of which cut airflow without anything looking wrong indoors. If the filter was black and the coil freezes again after a thaw, the duct system is the next suspect.
Cause two: refrigerant charge, and cause three: the blower or controls
If airflow checks out, the charge is low, and low charge means a leak. Refrigerant does not get used up. Common leak points are the indoor coil itself, the line set where it crosses a crawlspace, and service valves. This is not homeowner work and it is not something to top off and forget. A blower running slow, a failed capacitor, a bad motor module or a thermostat wired to run the compressor without the fan will also freeze a coil. Same with a clogged condensate drain that backs up and trips a safety switch, which stops the blower but not always the outdoor unit.
What you can safely check yourself
Turn cooling off at the thermostat and set the fan to ON so room air can melt the ice. That can take several hours. Do not chip at it and do not aim a heater at the coil. While it thaws, change the filter, check that supply and return vents are open and unblocked, confirm the thermostat batteries are good and the setting is correct, look for a tripped breaker, and clear leaves and grass clippings from around the outdoor unit. That is the full list. Anything involving refrigerant lines, gas or high voltage stops there and becomes a phone call.
What we do differently on an air conditioning repair call
We measure instead of guess. That means static pressure across the coil to prove whether airflow is the problem, temperature split across the supply and return, blower amp draw, and superheat and subcooling to judge the charge. If the numbers point to a leak, we find it rather than adding refrigerant and leaving. We also crawl the crawlspace, because in older ranches and colonials the answer is often a duct off its collar or a return pulling humid crawlspace air across the coil. You get told what failed, what it will take to fix, and what will freeze again if we skip it.
When it is time to book
A Frozen AC Coil and What Causes the Ice — straight answers
How long does it take a frozen coil to thaw?
Usually four to eight hours with cooling off and the fan set to ON. A heavy block of ice can take longer. Have towels ready, because all that ice becomes water and the drain pan may not keep up.
Can I just add refrigerant to stop it freezing?
No. Low charge means a leak, and refrigerant work is not homeowner work. Adding more without repairing the leak puts you back in the same spot in weeks and can damage the compressor in the meantime.
My filter was filthy and I changed it. Am I done?
Maybe. Let the coil thaw fully, run the system, and watch it for a few days. If ice returns, the filter was a symptom of a bigger airflow or charge problem and it needs measuring, not another filter.
How it works
- Step 1
Tell us the symptom
Call or fill in the form and describe what changed. Warm air, short cycling, a smell, water near the indoor unit. Details like that help us load the right parts before we leave.
- Step 2
We diagnose the whole system
We check the thermostat, the indoor unit, the outdoor unit and the ductwork, including runs in crawlspaces where damp air and loose joints quietly cause weak airflow and long run times.
- Step 3
You approve the fix
We explain what failed, what it takes to repair it, and what we would watch next season. Nothing gets replaced without your yes, and we clean up before we leave.
- A real person answers
- Open 7 days
- Written quote before work starts
Why homeowners call us
- Humidity is our home groundMuggy summers and damp shoulder seasons drive most of the calls we take. We look at moisture and airflow together, not the cooling number alone, because a clammy house often means a sizing or duct problem.
- Crawlspace ducts get checkedOlder homes across the region run supply ducts through vented crawlspaces. Crushed flex, disconnected boots and soaked insulation show up constantly, and we get under the house to look instead of guessing from the register.
- Heating and cooling bothSame crew for air conditioning repair in July and heating repair in January. We know how your furnace, heat pump and air handler share ducts and a blower, so one visit covers the whole system.
- Plain talk on repair or replaceWhen a repair makes sense, we repair it. When a system is failing in ways that will keep costing you, we say so and explain why, then leave the decision with you and your timeline.
- All major brands, gas & electricCarrier, Trane, Lennox, Goodman, Rheem, York and more, as an independent company.
- Straight answersIf a system is not worth repairing, we say so, often right on the phone.
About this guide
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- A real person answers
- Open 7 days
- Written quotes
- All major brands
- Gas & electric
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