is a sedona a minivan with 2 zone air/heat, if so it could be a secondary heater core.
I had the the same problem last summer. The rear heater lines cracked from rusting. My 2004 Sedona EX with rear AC/Heat leaked coolant thus ended up overheating the engine. Luckily no damage was done to engine and the vehicle was still under factory warranty. So the dealer had to replace the coolant lines which are tied in from the front all the way back to the rear heater core.
Cheaper repair - disconnect coolant hoses behind lines at the front tire area. Buy a small diameter coolant hose, u-shaped part No.10777 and two hose clamps part no. 70501012 at NAPA auto. Use slip joint pliers to remove old clamps, wiggle and gently twist to remove hoses. Put both new clamps around the u shaped hose and reattach with a screw driver. Results- car is totally drive-able until fixed with the very expensive dealer repair or drive that way with no heat to the rear seats.
The rear cabin heater uses coolant lines that run to a heat exchanger in the rear.
The 2004 Kia Sedona has 48.8 in. of rear hip room.
The 2012 Kia Sedona has 40.9 in. of rear leg room.
The 2007 Kia Sedona has 65.3 in. of rear shoulder room.
The 2006 Kia Sedona has 39.8 in. of rear head room.
The 2009 Kia Sedona has 39.8 in. of rear head room.
The 2002 Kia Sedona has 65.1 in. of rear hip room.
The 2007 Kia Sedona has 39.8 in. of rear head room.
The 2002 Kia Sedona has 63.1 in. of rear shoulder room.
The 2007 Kia Sedona has 65.8 in. of rear hip room.
The 2007 Kia Sedona has 37.0 in. of rear leg room.
The 2011 Kia Sedona has 65.3 in. of rear shoulder room.