The answer to 'system upgrade freezing up' is that this is a common issue that can be caused by a few different factors. The most likely causes are a refrigerant leak, a problem with the compressor, or a blockage in the system. Symptoms include the system freezing up, ice buildup, and reduced airflow or cooling capacity.
If your upgraded HVAC system is freezing up, the first step is to check the air filter and clean or replace it if it's dirty. You can also try increasing the fan speed to improve airflow. However, if the issue persists, it's best to call in a professional HVAC technician to diagnose and repair the problem. Attempting to fix a freezing system yourself can potentially cause further damage, so it's generally not recommended for homeowners to DIY this type of repair.