The answer to 'HVAC system high energy bills' is that there are several common causes, including an inefficient system, improper sizing, lack of maintenance, and issues with ductwork or insulation. Symptoms may include uneven heating/cooling, high utility bills, and the system running constantly.
Common solutions include upgrading to a more efficient HVAC system, ensuring proper sizing, regularly maintaining the system, sealing ductwork leaks, and improving insulation. For many of these issues, it's best to call a professional HVAC technician for diagnosis and repairs, as they have the expertise and tools to properly address the problem. Attempting DIY repairs can sometimes make the issue worse or even create safety hazards.