2004 Kia Sorento - Heater issue

heater will not blow hot, air blend actuator is working, air blend door seems to be functioning, hot fluid in and out of the core, dont know where else to look

Bad blower motor, maybe. Or bad resistor pack.

If tapping on the motor wakes it up, replace it or plan to soon. If the fan runs only on High the resistor pack needs to be replaced.

Blower works fine on all speeds, only problem is that i cant get hot air, cold works great on all speeds

Perhaps your suspicions are incorrect. Why not disconnect the actuator and position the door manually to verify it still does not blow hot air? The other possibility is the door has broken from the actuator lever. You may be able to tell when you try moving it by hand if there is any resistance indicating you are moving the door…

Tried that and i heard the door clunk when it opened and closed, plus i heard the air resistance change in the air box, what else could cause it other than the blower and air mix door and core?? Clogged vent?

Well, there’s not much to the system. You have hot water in and out and air blowing through the exchanger with the blend door selecting just heated air to the cabin. That leaves thermal transfer issues. Could be the interior of the exchanger tubing is coated with oxidation, sludge or something preventing heat transfer, the fins have rotted off the fluid pipes etc.

At the risk of asking something you already ruled out, does the air volume change significantly when switching from cold to hot?

It does change when going from cold to hot, maybe drops 25% or a little more, but at least im getting some ideas i havent checked yet, how would i check the heat exchanger and fins, is that part of the core?

Yeah, unfortunately that IS the core. If that’s it, my condolences. Envision the first part coming down a car assembly line…it’s the heater core hanging on a wire and then they build the rest of the car around it…

Hey, might be worth investing in one of those slick flexible shaft cameras so you can look at the core without taking it all apart…seen some reasonably priced ones lately and may take the plunge myself.

25% reduction shouldn’t result in cold air. Was thinking maybe a mouse nest or debris blocking core air flow…

What if the recirculate door is moving but the blend door is not? They’re sometimes close enough to each other that you can mistake the one for the other.

No i found both, and they both work and are in tact, it seems that the core being corroded or covered with something internally is the most logical option at this point, everything else has been checked and is working the way its supposed to