Hyundai Repair: AC VENT, air conditioning compressor, evaporator

Question
AC COLD BUT WHEN DRIVING 40 TO60 MINUTES VENT  STOPS COMING OUT.. I HEAR IT WORKING  BUT DOES NOT COME OUT VENT.. SHUT OFF CAR AND RESTART ITS OK AGAIN..

Answer
If you hear the fan running but no air flow (or reduced air flow) is coming out of the vents, this is a very large sign that the evaporator is freezing over.  Depending on the year and model of your vehicle, there should be a sensor in the evaporator which measures the evaporator temperature and turns off the air conditioning compressor when the evaporator gets too cold (and is in danger of freezing).  Most likely, this sensor is not working properly.