Ice on your air conditioning system is one of the more alarming things a homeowner can discover — but it’s also one of the most preventable problems I deal with.
Why does ice form?
Your evaporator coil operates at a very cold temperature when your system is running. Normally, warm air from your home blows across it constantly, keeping it from getting too cold. When that airflow is disrupted, the coil drops below freezing and moisture in the air freezes onto it. Once it starts, it compounds — ice restricts airflow further, causing more freezing.
The most common causes:
Dirty filter. By far the most common. When your filter is clogged, not enough air moves across the coil. In our dry Weber County climate, filters load up faster than people expect. Check yours every 30 days.
Dirty evaporator coil. Dust that gets past the filter coats the coil itself over time. A coated coil transfers heat poorly and is much more prone to freezing — a direct consequence of chronic filter neglect.
Closed or blocked vents. People close vents in unused rooms thinking it saves energy — it actually hurts the system and can cause freezing.
Oversized AC on undersized ductwork. I see this regularly. The system tries to push more air than the ducts allow, the coil gets starved for airflow, and freezing is the result.
Low refrigerant. A low charge causes the coil to run colder than it should, which can lead to freezing even with adequate airflow.
What to do when you find ice:
Turn off COOL at your thermostat. Switch to FAN ONLY if your system has it — this lets warm air defrost the coil without running the compressor. Do not chip or scrape the ice off; you can damage the delicate coil fins. Let it thaw naturally (a few hours), then call a technician. We cannot accurately diagnose a frozen system until everything is back to normal operating temperature.
The fix almost always starts with the filter. Start there.
By Gregg DeMille, owner of Timber Creek Services in Farr West, Utah.
Need help with this? See AC Repair or call or text (801) 832-5302.