Picked up N LX470 today for a good deal. AC wasn’t working so I took it to my friends shop to diagnose. He filled the refrigerant because it was no. Showed no signs of leaking after filling. Ac compressor would kick on for like 3 seconds then cut off. Relay is fine, he manually jumped the circuit in the relay box and it worked. Put the relay back and in and it AC still wont stay on. Any idea what it could be and how to fix?