You might want to hook up a set of gauges to see what kind of pressure you are running. If it is above 40 psi on the low side and above 350 on the high side, I would say it is time to have the a/c re-serviced. You could possibly have a little air in the system if you have a leak. I should run around 20 on the low side and 300 on the high side. This is just a guess. If there is a air-conditioner expert out there, lend a hand.