The answer to 'why is my HVAC system not cooling' is that there are several common causes, including a refrigerant leak, a malfunctioning compressor, a dirty air filter, or an issue with the thermostat. Symptoms may include warm air coming from the vents, the system running constantly, or high energy bills.
Some potential solutions include checking and replacing the air filter, ensuring the thermostat is set correctly, and inspecting for any visible refrigerant leaks. However, for more complex issues like a compressor failure or major refrigerant leak, it's best to call a professional HVAC technician to diagnose and repair the problem.