Ac works sometimes then will start to blow warm air and then back to cold after a short time

Is the radiator fan working? Is the A/C getting warm while driving or only when sitting still? Was the hose fixed by a professional or was the system properly vacuumed before the charge was added? Is it only cold when the compressor is engaged? Could be a low charge if the compressor is short cycling or there is a restriction in the expansion valve maybe. The best answer is to have it serviced again for a proper diagnosis.