There are several signs that may indicate a failing compressor in an HVAC system. These include unusual noises, such as knocking or clunking sounds, increased energy consumption, reduced airflow, and increased temperatures. Other signs may include compressor overheating, refrigerant leaks, or corrosion on the compressor or surrounding components. If you notice any of these signs, it’s essential to troubleshoot the issue promptly to prevent further damage to the system.