as above, if bridging the pins make the a/c come on, you have a pressure problem. its not the wiring or sensor because the sensor is new and this test has ruled out a wiring fault. if you're lucky when it was last filled the guy put in some dye, which you should be able to see escaping from the spot where it is leaking. otherwise a good a/c technician should be able to check the system over for you and locate the leak
