The answer to 'replacement not cooling' is that there are several common causes, including a refrigerant leak, faulty compressor, or issues with the air handler or ductwork. Symptoms may include the unit running constantly but not cooling the home effectively, warm air blowing from the vents, or the system freezing up.
For a new system that is not cooling properly, the first step is to check the air filter and clean or replace it if needed. You should also ensure the thermostat is set correctly and that the outdoor condenser unit is free of debris. If those simple fixes don't resolve the issue, it's best to call in a professional HVAC technician to diagnose and repair the problem. Attempting to troubleshoot or repair a cooling system yourself can be dangerous and may void the warranty, so it's generally not recommended for homeowners to DIY HVAC work beyond basic maintenance.