Usually the system pressure is too low so the safety switch prevents the compressor trying to compress something it can't. Common issue, seals go. Best to have the compressor rebbuilt at least once in the car's life.
Try just having a regas and new dryer/filter done first- that will do it for a little while, maybe longer
The above assumes the fan blower is on and working when you activate the AC, and that the small AC belt is intact and working of course.