Why Is My AC Freezing Up?

An air conditioner freezes up when something makes the indoor coil too cold, so moisture in the air turns to ice instead of draining away. The two main triggers are restricted airflow and low refrigerant.

Your evaporator coil normally runs cold but stays above freezing because warm household air keeps moving across it. When a dirty filter, closed vents, or a weak blower cut that airflow, the coil drops below freezing and ice builds. Low refrigerant does the same thing by lowering the coil temperature. Once ice forms, it blocks airflow even more, and the problem snowballs fast. Catching it early keeps a cheap fix from becoming an expensive one.

If you see ice on the copper lines or the indoor coil, turn the system from cool to off, and set the thermostat fan to on. Running the fan with cooling off blows warmer room air across the coil and melts the ice faster, usually within one to three hours. Never chip at the ice with a tool, which can puncture the coil.

While it thaws, replace a dirty filter and open any closed or blocked vents. Place towels under the indoor unit to catch melt water. Once everything is fully thawed and dry, you can try cooling again. If it freezes back up, stop and call us, because the underlying cause is still there.

If your AC keeps freezing, the root cause is usually one of a few things: a filter that clogs too quickly, a failing blower motor, a refrigerant leak, or a coil caked with dust that needs professional cleaning. Low refrigerant is especially common and always means a leak somewhere in the system.

Closed registers in unused rooms also choke airflow more than people expect, since the system was balanced for all vents open. Running an AC while it is iced over strains the compressor, the single most expensive part to replace. That is why a repeat freeze-up is a signal to shut the system down and have it diagnosed rather than nursed along.

Greater Baltimore summers are humid, and humidity is fuel for coil freezing because there is so much moisture in the air for ice to form from. In local homes we often see freeze-ups during long humid stretches when a marginal system is already running flat out.

Older county homes and rowhomes with long, restrictive duct runs are especially prone, and so are homes where vents in spare bedrooms get closed to save energy. We also find a lot of frozen coils that trace straight back to a filter that has not been changed in months. None of it is unusual, and most of it is preventable with airflow attention and a yearly tune-up.

Thaw the system, swap the filter, and open your vents. If it freezes again, leave it off and call us, because continuing to run it risks the compressor. A repeat freeze almost always means low refrigerant or an airflow problem that needs proper tools to diagnose.

Comfort Systems, Inc. has handled Baltimore-area cooling since 1995. We are fully licensed and insured under Maryland Master HVAC License #17072 and provide emergency service through the worst of the summer heat. We will find why it is freezing and fix the cause, not just the symptom, with honest pricing and no upsells. Call (410) 529-1879.