AC problems • Troubleshooting guide
Why Is My AC Freezing Up?
Frost on the copper line, ice on the indoor coil, and air that gets weaker the longer it runs. Ice means the coil is running too cold, for one of two reasons.
Or dial (213) 214-0220 — available 24/7.
The short answer
An air conditioner is not supposed to make ice. The indoor coil is designed to run just above freezing, and two things push it below: too little air crossing it, or too little refrigerant inside it. Either way the coil turns into a block of ice, airflow drops further, and the freeze feeds itself until the system is doing almost nothing except running.
The airflow causes are the ones you can influence: a clogged filter, closed or blocked vents, a dirty indoor coil or a blower that has slowed down. The refrigerant cause is a leak, which a technician has to find. The first step is the same in both cases: switch cooling off and let the ice melt completely, with the fan running if your thermostat allows it. Running a frozen system risks the compressor, the most expensive part in it.
Most common causes
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Clogged filter or blocked vents
Restricted airflow is the number one cause. Less warm air over the coil means less heat to keep it above freezing, so frost forms and grows.
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Low refrigerant from a leak
With less refrigerant, the pressure inside the coil drops and so does its temperature. Ice starts at the point where refrigerant enters the coil and spreads.
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Dirty evaporator coil
A film of dust on the indoor coil acts as insulation and blocks airflow at the same time. It builds up over years of running without filter changes.
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Blower motor running slowly or failing
A weak blower or a wheel caked in dust moves too little air even with a clean filter. The symptom is often a freeze plus a humming or labored indoor unit.
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Running the AC on a cool night
Cooling with outdoor temperatures in the low 60s or below, especially with a low set point, can freeze a healthy coil. Los Angeles coastal nights can do this in spring and fall.
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Kinked line or stuck metering device
Less common: a restriction in the refrigerant circuit starves the coil the same way a leak does, and the fix is very different from a recharge.
Safe checks before you call
None of these involve opening the equipment, touching wiring or bypassing a safety switch. If a check needs a tool or a panel removed, it is not on this list on purpose.
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Switch cooling off and let it thaw
Set the thermostat to Off, or to Fan On if it has that option, and give the ice at least a few hours to melt. Do not chip at the ice or pour hot water on the coil.
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Check the filter while it thaws
A filter you cannot see light through is a likely cause. Replace it with the same size before the next test run.
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Open every supply and return vent
Closed bedroom registers and a return grille hidden behind furniture reduce airflow more than most people expect.
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Put towels under the indoor unit
A thawing coil releases a lot of water. Catch it so the melt does not become a second problem.
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Note the outdoor temperature
If the freeze happened on a cool night with the AC set low, the system may be healthy. If it freezes again on a warm afternoon after the filter change, it needs a visit.
Stop and call if…
How an AC24Repair technician diagnoses this
The technician needs the coil thawed to test properly, so if it is still iced they will ask you to keep cooling off until the visit. Then they measure airflow first: filter, coil condition, blower speed and current draw, and the static pressure in the ducts. That separates the airflow freezes from the refrigerant freezes.
If airflow is healthy, gauges go on the outdoor unit to read the refrigerant pressures and the temperatures at the coil. Low readings mean a leak, and the technician then searches for it rather than simply adding refrigerant, because a recharged leak freezes again in weeks. A restriction shows up as a different pressure pattern and gets a different repair. You get the cause, the repair and the price before work starts.
Repairs that may follow the diagnosis
Which one applies, and what it costs, depends on what the technician finds. You hear the price before any work starts.
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Airflow restoration
Filter replacement, evaporator coil cleaning, register and return corrections or duct repair to bring airflow back to what the coil needs.
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Blower motor or wheel service
Cleaning a caked blower wheel or replacing a failing motor so the indoor unit moves the designed amount of air.
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Refrigerant leak repair and recharge
Locating the leak, repairing or replacing the leaking section, evacuating and recharging to the correct charge.
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Metering device or line repair
Clearing or replacing a restricted component when the pressure readings show the refrigerant is not flowing rather than missing.
Clear pricing before the work starts.
Diagnostic visit fees depend on the time of day. We publish the confirmed diagnostic fees and explain the repair price before work begins.
Help with this across Los Angeles
Technicians come to homes in the San Fernando Valley, West, Central and Northeast Los Angeles.
AC freezing up: questions homeowners ask
Can I speed up the thaw with a hair dryer?
Please don’t. Heat, tools and water near the coil and its wiring cause more problems than they solve. Fan On mode and patience do the job safely.
Why does it freeze only at night?
Cool outdoor air and a low set point lower the coil temperature below freezing even on a healthy system. Raising the set point at night, or using a schedule, usually prevents it.
Is ice on the outdoor unit the same problem?
Ice on the outdoor unit during cooling season is rare and usually signals a serious refrigerant issue or a heat-pump defrost fault. Switch the system off and call.
If it is low on refrigerant, can you just top it up?
We can add refrigerant, but only after finding and fixing the leak. A top-up alone is a temporary patch and you would be paying for it again by the next heat wave.
How long after the thaw before I can run it again?
Once the coil and lines are completely free of ice and the filter is clean, run it and watch. If frost returns within an hour, leave it off and book a visit.
Tell us what’s happening. We’ll take it from there.
Call any time. We schedule a technician within 24 hours and explain the price before repair work starts.
Or dial (213) 214-0220 — available 24/7.