It does go on and off as your temp. settings in the cabin control a thermostat. When the temp goes down to the thermostat setting (Temp you set in the cabin...68, 70, 72, etc.) then the A/C goes off until the temp rises and then it comes on again to cool down to that point. The fan will keep blowing during this time. If you have the vent wheel to the left of the center vents (closest to the instrument dash) turned all the way up, when the A/C clicks off, you'll get outside air inter your cabin. If it is extra hot outside, this air may feel hot and make you feel as if your A/C is not cooling. Try turning this wheel all the way down and off in that case. If all this doesn't do the trick and your A/C is cycling off and on rapidly then you are probably low on coolant and need a boost, or worst case senario is that your evaporator is leaking which could be a major repair and $$.
--
1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon