A/c problem

I have a 1991 Grand Am with 2.5 Lt. engine. Several days ago while going down the interstate it stopped blowing cold air.Later I checked it and the clutch is still engaged.apparently turning the compressor. I put a gauge on the low side and the pressure is 90 with the motor running. It appears the compressor is not working. I was told there might be a blockage in the ofrice tube. Is there any way to find out what the problem is before just taking it all apart? Would the compressor just quit even though it is still turning?