It’s the middle of July on the Emerald Coast, the temperature is pushing 95 degrees, and suddenly your air conditioner stops blowing cold air. You go outside to check the unit and find the refrigerant lines covered in a thick layer of solid ice. Why does an AC unit freeze up when it’s so incredibly hot outside?
The Science of a Frozen AC
Your air conditioner doesn’t actually “create” cold air; it removes heat from the air inside your home. It does this by blowing warm indoor air over the evaporator coil, which is filled with extremely cold liquid refrigerant. The refrigerant absorbs the heat, turns into a gas, and carries the heat outside.
For this process to work, there must be a constant, steady flow of warm air over the coil. If that airflow is restricted, or if the refrigerant gets too cold, the condensation that naturally forms on the coil will freeze. Once a thin layer of ice forms, it acts as an insulator, making the problem worse until the entire coil is encased in a block of ice.
The Top 3 Causes of a Frozen AC
If your AC is frozen, it is almost always caused by one of these three issues:
- A Dirty Air Filter (Restricted Airflow): This is the most common cause. A clogged air filter blocks the warm air from reaching the evaporator coil. Without that warm air, the coil drops below freezing, and the condensation turns to ice. Solution: Check and replace your air filter every 30-60 days.
- Low Refrigerant (A Leak): It sounds counterintuitive, but low refrigerant actually makes the coil colder. When the pressure inside the system drops due to a leak, the temperature of the remaining refrigerant also drops, causing the coil to freeze. Solution: A licensed HVAC technician must find the leak, repair it, and recharge the system.
- A Dirty Evaporator Coil: If the coil itself is covered in a layer of dust and dirt, the dirt acts as an insulator, preventing the refrigerant from absorbing heat from the air. Solution: Professional AC maintenance includes a thorough cleaning of the evaporator coil.
What to Do If Your AC is Frozen
If you discover your AC is frozen, turn it off immediately. Continuing to run a frozen AC will force the compressor to work overtime, which can cause it to burn out—resulting in a massive repair bill or the need for a complete system replacement.
Turn the thermostat from “Cool” to “Off,” and turn the fan setting from “Auto” to “On.” This will blow warm air over the frozen coil to help it thaw faster. Do not try to chip the ice away with a tool, as you can easily puncture the delicate refrigerant lines.
Call the Experts at Advantage HVAC
Once the ice has melted (which can take several hours), check your air filter. If it’s clean, you likely have a refrigerant leak or a more serious mechanical issue. Call Advantage HVAC, Plumbing & Electrical at 850-GET-ANDY (850-438-2639). Our expert technicians will diagnose the root cause of the freeze-up and get your home cooling reliably again.