The answer to 'HVAC system not cooling' is that there are several common causes, including a refrigerant leak, a faulty compressor, a dirty air filter, or issues with the thermostat. Symptoms may include the air coming out of the vents not being cold, the system running constantly, or the home not reaching the set temperature.
If you suspect an HVAC issue, first check the air filter and replace it if it's dirty. You can also try adjusting the thermostat to see if that resolves the problem. However, if the issue persists or you're unsure of the cause, it's best to call a professional HVAC technician to diagnose and repair the problem. Attempting DIY repairs on an HVAC system can be dangerous and may void the warranty, so it's generally recommended to have a licensed technician handle any major repairs or maintenance.