On hot days the a/c cools ok. On very hot days the a/c barely does anything. Also I hear a clicking sound about every 5 seconds or so. Think it needs a recharge since I have never serviced the a/c having owned the car for 10 yrs. Car runs great however. Would like to know how I can charge it myself? Bought a can of the r134a with guage attached. Not sure of location to hook up and how to unscrew cap. please advise.