The answer to 'system upgrade blowing cold air' is that the most common causes are improper installation, refrigerant leaks, or problems with the new system components. Symptoms may include the air coming out of the vents feeling much colder than normal, the system cycling on and off frequently, or the home not reaching the desired temperature. Solutions can range from adjusting the thermostat settings, to repairing refrigerant leaks, to replacing faulty parts.
For a system upgrade, it's best to have a professional HVAC technician handle the installation to ensure it's done correctly and the new system is properly sized and integrated with your home. Attempting a complex system upgrade as a DIY project can lead to further problems and is generally not recommended. However, some basic troubleshooting steps like checking the thermostat or air filters may be suitable for homeowners to try first.