I have a 2010 Journey SXT with the 3.5 and this was my experience with this problem. I spent week's on forums and online trying to figure out what was going on and everyone kept saying heater core. There was no way in hell i was going to pay over 1k to have the core changed at a shop. I ordered a heater core from Rockauto and changed it myself ($80.00 with shipping). Now.... Was i going to take the dash out for a simple 5 minute swap out? NO. I cut the lines and attached them with heater hose and clamps. Prior to this i drained the old coolant and flushed the complete system as best as i could them attached the new core and added new coolant. Problem solved. NO. Hot air on the drivers side cold air on the passanger side. What the heck. Looked at the blend door actuators and all seemed to be working fine but i pulled the passenger side actuator off to inspect. Opened it up and found teeth missing from one of the gears. Ordered a new one of amazon ($23.00) and installed. Keep the old one because you may need to change the connection gear on the new actuator from the old one. Installed and...... Man still no heat on the passenger side. Removed drivers side acuators to inspect and all were good. Maybe the a temp control modual on the dash? Nope. Works fine. Need more time to figure it out. A few months passed, its starting to get cold and im starting to lose all heat. Inspected and discover my coolant tank is leaking. Maybe that was the problem all along. Not enough pressure building up. Ordered a new tank and thermostat from Rockauto ($60.00) and installed. Finally didn't have to worry about no heat on passenger side because now i have no heat period. At this point im ready to use a sledgehammer on this POS. Go through the entire system again to see if i missed something but everything checked out to be in proper working order. Now, i dont know what to do or what my next move is. While the drivers side lower panel was off, i looked at the heater core again and took a long shot at trying something. I grabbed my prybar and used the handle to lightly tap the bottom outlet tube. I did this while the vehicle was running and i noticed it kept getting hotter and hotter and on both drivers and passenger side. Lightly tapped it for a few more minutes, turned the vehicle off untill the next day. Started it and let it get hot. No problem what so ever. Heat is just blasting out of the vents on both sides. Long story short. Most likely if you have heat on only one side or no heat and you have changed parts, you will probably end up with a air pocket in the system. Bleed the system as best as you can. In total, i spent a few hours and around $250 to do the work and i actually have to turn the heat down now while driving.
