The answer to 'AC not working' is that there can be several common causes, including a faulty thermostat, low refrigerant levels, issues with the compressor or condenser, or problems with the electrical system. Symptoms may include the AC unit not turning on, poor airflow, warm air coming from the vents, or the unit cycling on and off frequently.
For simple issues like a dirty air filter or thermostat problems, homeowners may be able to troubleshoot and fix the issue themselves. However, for more complex problems involving the refrigerant, compressor, or electrical components, it's best to call in a professional HVAC technician. Attempting DIY repairs on these parts can be dangerous and may even void the warranty.