If you're certain that the blend actuator is working properly and your vehicle doesn't have a dual-zone climate control system, there might be a more specific issue causing the temperature imbalance between the driver's and passenger's side vents. Given the circumstances, you might want to consider the following possibilities:
Low refrigerant: Check refrigerant level. Low refrigerant levels in the air conditioning system can cause the symptoms you described, where the air isn't as cold as it should be. When refrigerant levels are low, the evaporator coil may not get cold throughout to fully cool the air passing over it, resulting in warmer air coming out of one side vents.
If the refrigerant level is low, it could be due to a leak in the system. Refrigerant leaks can occur over time and may need to be identified and repaired.
Temperature Control Cable/Linkage: In vehicles without electronic blend actuators, a cable or linkage system is often used to control the temperature blend door. If this cable or linkage is misaligned, damaged, or not functioning correctly, it could result in the driver's side vents receiving warmer air than desired.
Temperature Blend Door Calibration: Sometimes, the temperature blend door needs to be calibrated properly to ensure accurate temperature control. Even though the blend actuator itself might be working, it's possible that the calibration is off. This can sometimes be reset by disconnecting the vehicle's battery for a short period of time, or there might be a specific procedure outlined in the vehicle's manual.
