The answer to 'why is my HVAC system' is that there could be several common causes, such as a malfunctioning thermostat, clogged air filters, refrigerant leaks, or issues with the compressor or blower motor. Symptoms may include poor airflow, uneven heating/cooling, high energy bills, or the system not turning on at all.
Some simple DIY troubleshooting and maintenance tasks you can try include checking the thermostat settings, replacing air filters, and ensuring the outdoor unit is clear of debris. However, for more complex issues like refrigerant leaks or electrical problems, it's best to call in a professional HVAC technician to properly diagnose and repair the system.