Assuming that it is non -climatronic manual control under the SERCA battery of the radiator carries a relay module with 2 plugs one of 4 pins O0tro of 14 pins this is responsible for activating first and second of the fans with the second a/Cy with the engine heating and remove positive vel from the compressor.
As you say activates the first of the fans and not the compressor 2 probable things The compressor coil if the positive one that should reach the coil puts a tester and turns on and turns off your tester does not work the coil to get out of doubt looking for any vobine and connect it to the original compressor connector of the compressor. From relays because if you activate the fans it means that all the signals are working, I tell you because I dedicate myself to this greetings from Cancun