Ac Works and it Doesn't ???

[mestasmail]

whats up guys I am having a little problem w/my 2001 325i. On my gauge cluster my temp gauge is reading -30 derees. My ac is turning on the heater when i switch to the vents by the windsheild. When they point towards your face the fan works just blowing air then you hear a whistle the compressor turns on and bam air works for a little while and the cycle just repeats. So my question is ac compressor? Cut off Switch? Low freon? or none of the above??? This is my First Bmer So I'm a-little new to the german stuff? Thanx Guys!!! [bmwdance]