How do you know if the fan relay is faulty?

You can determine if a fan relay is faulty by checking for signs such as the fan not turning on when it should, or if it runs continuously without stopping. Additionally, testing the relay with a multimeter for continuity when activated can help confirm its functionality. If the relay clicks but the fan still doesn't operate, it may be defective. Lastly, inspecting for any visible damage, burnt contacts, or corrosion can also indicate a problem.