Why is my AC freezing up?

An AC freezes when the indoor coil gets too cold to shed moisture as water, so the moisture turns to ice. The usual causes are restricted airflow, a dirty coil or low refrigerant. Refrigerant doesn’t get used up, so low charge means a leak somewhere. Airflow problems usually start at a clogged filter.

Climate Pros Tucson is a referral service. The licensed pro you’re matched with diagnoses the cause.

What should you do first?

  1. Turn the cooling off at the thermostat.
  2. Set the fan to on so air moves over the coil and speeds the melt. If ice is heavy, turn the whole system off.
  3. Let the ice melt completely. Don’t chip it.
  4. Place towels under the indoor unit in case of meltwater.

Running a frozen system can damage the compressor.

What causes ice in a Tucson home?

  • Dirty filter or blocked return. Desert dust and dust storms during the monsoon load a filter quickly. See the dust-focused filter guide.
  • Closed or blocked vents that cut airflow across the coil.
  • Dirty evaporator coil, which hides the coil from air.
  • Low refrigerant from a leak. Topping off without finding the leak only delays the next freeze. See signs of a refrigerant leak.
  • Blower or fan problems that slow airflow.
  • Clogged condensate drain, which shows as water rather than ice but often goes with a freeze. See clogged AC drain lines.

Does monsoon humidity make freezing more likely?

It adds load. Tucson’s monsoon runs June 15 to September 30, and at the airport average dew points jump from the 20s into the high 50s in July and August. Wetter air means the coil handles more moisture, so any airflow or charge problem shows up faster. Humidity alone doesn’t cause ice. A problem with airflow or refrigerant does.

When should you call a pro?

Call when ice comes back after a thaw with a clean filter, when ice forms on the outdoor line, or when you suspect a leak. A pro uses gauges to find low charge, and EPA rules require Section 608 certification for people who service refrigerant systems. See AC short cycling if the unit also starts and stops often.

A pro handles AC repair for the freeze itself. Spring HVAC maintenance gets the coil and filter checked before June. The Tucson HVAC hub lists our coverage.

When to call us

Call (520) 353-2520 and we’ll match you with a licensed local pro. Tell the pro the unit froze, when it first happened and what you already tried.