Air conditioning only works intermittantly on 2003 BMW 525i

The air conditioner does not work most of the time. There is only cold air blowing out occassionally. Most of the time, the fan just blow normal outside air which is pretty hot in this summer season.

Asked by for the 2003 BMW 525i
Front fan or low on gas

Check the stratification settings
Thanks for your answer. What is stratification settings, and where can I find it in the car.