Why is my car AC freezing up?

Ice on the AC lines or an evaporator that frosts solid means the coil is dropping below 32°F and cabin humidity is freezing onto it, choking off airflow until you shut the system down and let it thaw. The usual triggers are low refrigerant (pressure drops, so does the evaporator temperature), a stuck-open expansion valve or orifice tube, a failed evaporator temperature sensor or cycling switch, or a filthy cabin air filter starving the coil of the warm air it needs to stay above freezing. Another recharge on top of an icing system just repeats the cycle.

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