When the evaporator coils on an air conditioning unit become too cold, the ac unit pipes freeze. This is the primary reason behind frozen AC lines. The evaporator coils inside an air conditioning unit are filled with refrigerant. A properly functioning AC system extracts the warm air from inside your home and sends it through your air conditioner, where the evaporator coils cool the warm air, then redistribute it back into the home.
If the airflow leading into the air conditioner is obstructed, it can cause the evaporator coils to become too cold, therefore causing the copper lines attached to your condenser to freeze. Here are some common factors as to why an air conditioning system can develop poor airflow: