A/C cuts on and off - I think I need to recharge it.

Good Day, This a/c problem is related to a recently purchased 99 Jeep Cherokee w/ 131000 miles. I noticed that when I start the a/c it continually cycled on and off. I looked under the hood and saw that the clutch, I think it is called, is what is cycling at what seems to be regular intervals and consequently the interior of the car never cools down, it not to long ago did work. I listened closely and could hear the related relay click, I assume it closes just prior to the clutch starting the cycle sequence. That led me to think that perhaps the relay is not functioning properly. I was wrong and I found that the new relay has the same resistance across the coil (75+ ohms) as the original one. At this point I need to recharge the system. Thank you