High Priority — Stop Running AC
AC Freezing Up?
What to Do Right Now
Ice forming on your AC’s copper lines, evaporator coil, or outdoor unit. Turn off cooling immediately — running a frozen AC can destroy the compressor, turning a $300 repair into a $3,000 replacement.
First Step: Turn AC Off, Fan ON
Set thermostat to OFF or FAN ONLY. Let the ice thaw for 2–3 hours before restarting.
Common Causes
Ice on your AC always means something is wrong with airflow or refrigerant. Here are the usual culprits.
1
Dirty Air Filter (Most Common)
A clogged filter restricts airflow across the evaporator coil. Less air = coil gets too cold = moisture freezes on the coil surface. This is the cause about 40% of the time and costs $5–$20 to fix (the price of a new filter).
2
Low Refrigerant
Counterintuitively, low refrigerant causes the evaporator to get colder than normal (lower pressure = lower boiling point). The coil drops below freezing and ice builds up. Low refrigerant always means a leak somewhere in the system.
3
Blocked or Closed Vents
Multiple closed supply vents restrict return airflow to the coil, same effect as a dirty filter. Furniture blocking returns, closed registers in unused rooms, or collapsed ductwork all contribute.
4
Blower Motor Issue
The indoor blower motor is slowing down or failing. Even with a clean filter, reduced fan speed means insufficient airflow. Listen for unusual sounds — grinding, squealing, or the fan running noticeably slower than normal.
5
Running AC Below 60°F Outside
Standard AC systems aren’t designed to run when outdoor temps drop below 60°F. Bay Area evenings can get cool even in summer — if you run AC at night when it’s 55°F outside, the coil can freeze. Use fan-only mode on cool nights.
What to Do Right Now
Follow these steps in order. Do NOT try to chip or scrape ice off — you can damage the coil.
Step 1: Turn off cooling. Set thermostat to OFF or switch to FAN ONLY. This stops the compressor while the fan continues circulating air to help thaw the ice.
Step 2: Check and replace the air filter. Pull out the filter. If it’s dirty, replace it now. Don’t restart cooling until the ice has fully thawed (2–3 hours).
Step 3: Open all vents. Walk through the house and make sure all supply and return vents are open and unblocked by furniture, curtains, or rugs.
Step 4: Wait 2–3 hours. Let the system thaw completely. Place towels under the indoor unit to catch water. Don’t restart until all visible ice is gone.
Step 5: Restart and monitor. Turn cooling back on with the new filter. If ice returns within 24 hours, you likely have a refrigerant leak or blower issue — call a technician.
Signs You Need a Professional
Ice returns after filter replacement and thaw — likely a refrigerant leak. The filter wasn’t the root cause.
Hissing sound near refrigerant lines — active refrigerant leak. Requires EPA-certified leak detection and repair.
Indoor fan sounds weak or makes grinding noises — failing blower motor. Needs replacement before it fails completely.
System freezes up repeatedly (chronic issue) — could be undersized ductwork, undersized system, or a metering device problem. Requires professional diagnosis.
Never run a frozen AC. Running the compressor while the coil is iced over forces liquid refrigerant back to the compressor (“liquid slugging”). This can crack the compressor’s internal valves — a catastrophic failure that usually means full system replacement.
Why Choose North Breeze
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EPA 608 certified
5.0 rated
Leak detection
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Frequently Asked Questions
The two most common causes are restricted airflow (dirty filter, closed vents, failing blower) and low refrigerant from a leak. A dirty filter is the #1 cause and costs under $20 to fix. If the filter is clean and the AC still freezes, you likely have a refrigerant leak that requires professional repair.
Yes — seriously. Running a frozen AC forces liquid refrigerant back to the compressor, which is designed to pump gas, not liquid. This “liquid slugging” can crack internal valves and destroy the compressor. A $300 refrigerant repair becomes a $3,000 compressor replacement. Always turn off cooling at the first sign of ice.
Typically 2–3 hours with the fan running. Severe ice buildup can take up to 4–6 hours. Set the thermostat to FAN ONLY to circulate warm air across the coil. Place towels under the unit to catch meltwater. Do not restart cooling until all ice is completely gone.
AC Keeps Freezing Up?
If your AC freezes after a filter change and thaw, you need professional diagnosis. Same-day service available.
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Leak Detection
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