A 99 lumina only blows cold out of two vents and the other two hot why?

In a 1999 Chevrolet Lumina, if two vents are blowing cold air while the other two are blowing hot, it could be due to a malfunctioning blend door actuator. This component controls the mix of hot and cold air; if it's stuck or broken, it may not properly regulate airflow to all vents. Additionally, there could be issues with the HVAC system, such as a low refrigerant level or a blockage in the ductwork. It's advisable to have the system inspected by a qualified mechanic for accurate diagnosis and repair.