By Robert Patterson
The short answer: an AC freezes when the coil gets too cold because airflow is restricted or refrigerant is low. Turn the system OFF (fan ON to thaw), replace a dirty filter, and if it refreezes, call — running a frozen system can wreck the compressor.
What causes an AC to freeze up?
Three usual suspects: restricted airflow (dirty filter, closed vents, a too-high MERV filter, or dirty evaporator coil), low refrigerant from a leak, or a failing blower. All of them let the coil drop below freezing and condensation turns to ice.
What to do right now
Switch the thermostat to OFF and the fan to ON to melt the ice (an hour or more). Swap a dirty filter, open any closed supply vents, and give it clear airflow. If it cools normally afterward, great; if it ices again, that points to refrigerant or a coil problem.
The failure mode to avoid
Running a frozen system anyway. Ice starves the compressor of proper refrigerant flow and a compressor is the most expensive part to replace — the kind of damage that flips a repair into a replace decision. When in doubt, shut it down.
Your next step
A refrigerant leak or dirty coil needs a TDLR-licensed tech — book AC repair or, in the heat, 24/7 emergency service. Prevent repeats with the $159/yr maintenance plan. More in the Learning Center.