The ac stops working after about 30 minuets of starting the car.

Hello, If the airflow is stopping, the cabin air filter, blower motor resistor, and blower motor should be checked. The filter can clog, especially if there is condensation in the A/C evaporator case, and the blower motor resistor may be getting hot and stopping. The other thing is that a refrigerant system issue could be at play. That would be the case if the vents still blow air, but the air is warm.