replace a HVAC temperature door actuator in their 2019 Toyota Sienna?

Hi - I am Dave, contributing to RepairPal and providing expert advice since 2010. The temperature blend door actuator may be the culprit, but you'll really want to have testing to verify the refrigerant system is working properly, and that you are not able to change the temperature at all - no matter what the climate control system is saying it is set at. If you can verify all that - then yes, the actuator -- or the plastic door it turns - may be at fault. Tear down to inspect and repair is needed. Reach out to a shop near you for assistance -- https://repairpal.com/auto-repair-near-me Click the link to find some shops near you who can help out!