Turn on the ignition switch, and then use your ears or stethoscope to listen to whether there is a sound in the control relay, or feel whether the relay is vibrating with your hands. If there is, the relay is basically working normally, and the electrical appliance is not working due to other reasons; otherwise, it means that the relay works abnormally.
You can also unplug the relay for testing. For example, if the air conditioner compressor does not work, you can start the engine, and then turn on the blower switch and the air conditioner switch. Then unplug the connector of the air conditioner compressor relay to judge. If the sound of the relay action can be heard, and the engine speed drops significantly when the relay is unplugged, and the engine speed increases when the relay is inserted, it indicates that the air conditioner compressor relay and its control circuit are normal.
Regarding the location of the relay, all relays and fuses marked with a dash on the schematic circuit diagram are generally arranged in the central distribution box.