Where is the blend door actuator located on 2003 Kia Sedona

There are a number of other causes more likely than the control valve.

low coolant level or air lock.
blocked heater core.
stuck thermostat
blend door actuators

https://www.google.com/search?q=KIA+Sedona+2006+heater+valve+location

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A full set of hand tools.

If you have dual range heating system (separate for driver and passenger), you have two blend doors. If you're only getting heat on the driver's side, the passenger blend door actuator is not working. It's possible this can be serviced without having to remove the entire HVAC box, but you would have to check for sure in a service manual, or a Haynes of Chilton repair manual.

Yes the fix is to remove the dash from the car and replace the blend door and the blend door actuator.

Not to difficult but you may need to get smaller tools to make it easier or possible depending on the tools you have now.

usually it is in the dash and the glove box needs to be removed to get to the actuator.

yes, actuator--black box with motor and gears inside that rotates the blend door. I think yours is right on the front of the heater box, to the right of center under dash. Remove actuator and check door for proper operation. If it opens and closes smoothly by hand, replace the actuator. If the door is sticking, you will probably have to take the heater box out of the car, split it open, and repair whatever is keeping it from opening.

Component locations...