Why evaporator's coil freeze-ups:
Sometimes evaporator coil is blocked with ice, because is dirty ,also there is some dust or debris on filters that restricts air flow and as a result temperature on evaporator's coil drops below freezing point. It is very important to do seasonal preventive maintenance to avoid this problem.
Other reason is when there's a leak on system and in consequence lower level of refrigerant therefore the pressure drops allowing moisture that becomes icing the coil. In this situation there's no transfer of heat, the coil is ice blocked so the airflow is blocked. so the unit is not cooling.
What you can do immediately is turn the unit off to permit the block of ice melt by itself and bring a HVAC certified Technician to do troubleshooting or maintenance , repair leaks and refill with refrigerant.