What's actually happening
An AC coil cools by boiling refrigerant. If the coil surface drops below 32°F and there's enough moisture in the air (there always is in Texas), water condenses and freezes. Once ice forms, airflow drops further, and the freeze accelerates.
Two things make the coil too cold: not enough warm air passing over it (airflow), or too little refrigerant boiling inside it (charge).
Airflow causes
Clogged filter, closed or blocked supply vents, undersized returns, a dirty blower wheel, a failing capacitor slowing the blower, or an evaporator coil coated in dust and biofilm.
The single most common cause across Central Texas is a filter that's been in place longer than the homeowner remembers.
Refrigerant causes
A leak lowered the charge, or the system was undercharged from the last service. Low charge means less refrigerant to absorb heat, so the coil runs colder than design.
You cannot fix low charge by adding refrigerant without finding and repairing the leak. That's how systems get overcharged, damaged, and eventually replaced.
What to do right now
Turn the system to OFF (not just up on temperature). Turn the fan to ON to help melt the ice faster. Change the filter. Once the ice is gone, run the system and see if it repeats. If it does, call for diagnostics — running a frozen system damages the compressor.