I am going to take a WAG at something. There are two relays on the firewall, hidden behind the air filter canister. One is for AC and the other is for the fuel pump. They are identical relays and totally interchangeable. It might be possible that the AC relay is stuck. Try unplugging both to see if the fan stops running. If it stops, plug one harness in at a time to see if it starts up again. If so, get a new relay.