If your air conditioner is frozen solid with ice coating the indoor evaporator coil or outdoor copper suction line, turn your thermostat from "COOL" to "OFF" immediately, and turn the fan setting from "AUTO" to "ON" to circulate warm air across the ice. Continuing to run a frozen system can permanently burn out the compressor motor. The two root causes are almost always severe airflow restriction (usually a dust-clogged 1-inch air filter or closed supply vents) or low refrigerant caused by a pinhole leak.
During Delaware County summer heatwaves, finding ice on an air conditioner running on a 95°F day seems counterintuitive. However, without proper airflow or refrigerant pressure, coil temperatures plummet below 32°F, freezing atmospheric humidity into a thick block of ice.
The 3 Immediate Steps to Take When Your AC Freezes
- Turn Cooling OFF Immediately: Operating an AC with a frozen coil prevents liquid refrigerant from boiling off. Liquid refrigerant enters the compressor crankcase, diluting lubricating oil and destroying internal valves.
- Switch the Fan Setting to "ON": Running the indoor blower continuously forces warm indoor air through the air handler, accelerating melting. It typically takes 2 to 6 hours to completely thaw an iced coil.
- Monitor the Condensate Drain: Melting ice produces gallons of water. Place towels around the basement air handler or attic drain pan to ensure water exits cleanly through the drain line without overflowing.
The 2 Root Mechanical Causes Behind Frozen Coils
Once the ice has completely thawed, the underlying failure must be corrected before restarting cooling:
- Choked Airflow (80% of Cases): A pleated air filter coated with dust, hair, and pollen blocks warm room air from passing over the cold evaporator coils. The refrigerant inside the tubes cannot absorb heat, dropping coil temperatures below freezing. Blower motor failures and collapsed duct flex runs also trigger airflow freezes.
- Refrigerant Circuit Pinhole Leak (20% of Cases): When a system loses refrigerant through a corrosion leak, the pressure inside the evaporator coil drops. Following the ideal gas law, lower pressure yields lower boiling temperatures. The coil drops below 32°F, freezing ambient moisture.
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When to Call for Refrigerant Diagnostics
If your filter is clean and your coil freezes again within hours of thawing, a technician must perform an electronic leak search and check operating superheat and subcooling. Visit our AC repair page or call (321) 478-0693 for 24/7 service.