For about a month now, my wife has been complaining that the rear AC in her 2003 Yukon Denali has been blowing hot air only. This wasn't a huge problem until the summer temps started creeping up here in Colorado. I finally knuckled down and did some investigating today. Long story short, the blend door itself is busted and was stuck in the heating direction. Now for the long story. This could also serve as a general rear climate conditioning overview as I tried to get some pretty informative pictures along the way. This is where the project begins: 20170604_181933 by Wes 03 Yukon posted Jun 4, 2017 at 11:52 PM Remove the upper rear pillar trim, the black screw in anchor, the grey plastic trim clip, and the rear floor trim. This will allow removal of the quarter panel trim. There are two small tabs on the 12V outlet... 20170604_181950 by Wes 03 Yukon posted Jun 4, 2017 at 11:52 PM ... and one small relief in the trim panel. 20170604_181955 by Wes 03 Yukon posted Jun 4, 2017 at 11:52 PM Slide one tab out, then rotate the outlet until the other one slides out. After removing the trim it looks like this: 20170604_182048 by Wes 03 Yukon posted Jun 4, 2017 at 11:52 PM After some online reading I decided to begin troubleshooting at the blend door actuator. 20170604_182056 by Wes 03 Yukon posted Jun 5, 2017 at 8:14 AM I removed the actuator and took the cover off to inspect the internals. 20170604_182132 by Wes 03 Yukon posted Jun 4, 2017 at 11:55 PM Everything looked fine so I reconnected the wire plug and turned on the ignition. The actuator came to life and appeared to be working normally. Slightly dismayed, I started to put the actuator back on, but something didn't feel right. The blend door arm that is driven by the actuator looked like this when I first pulled the actuator: 20170604_182152 by Wes 03 Yukon posted Jun 4, 2017 at 11:55 PM And after attempting to reinstall the actuator, the arm looked like this: 20170604_182211 by Wes 03 Yukon posted Jun 4, 2017 at 11:55 PM Removal of the heater core by removing the plastic retaining shield and sliding it out, 20170604_182712 by Wes 03 Yukon posted Jun 4, 2017 at 11:56 PM allowed me access to retrieve the broken chunk of blend door. 20170604_182204 by Wes 03 Yukon posted Jun 4, 2017 at 11:55 PM 20170604_185642 by Wes 03 Yukon posted Jun 4, 2017 at 11:56 PM 20170604_185706 by Wes 03 Yukon posted Jun 4, 2017 at 11:56 PM I could not find any foreign objects that blocked the door, so my suspicion is that the door somehow bound up and the activator just kept turning. In my attempts to find a solution I also removed the blower motor hoping for better access. 20170604_182427 by Wes 03 Yukon posted Jun 4, 2017 at 11:55 PM However, the air discharges out the back of the housing, so I couldn't reach the blend door, but it did let me squeeze my hand behind the unit to find the linkage that attaches the two doors together. On a side note, if you attempt to remove the outer top housing you simply remove all the metal clips, but there are two hidden screws just to the left of the blower that attach the outer to the inner housing. 20170604_182953 by Wes 03 Yukon posted Jun 4, 2017 at 11:56 PM That's as far into the project as I went for the time being. I slid a piece of Tek Foil insulation in below the heater core and closed the blend doors. I put the insulation in just in case the doors fall back open while the truck is being driven. What really matters is that I turned on the AC and it blew out ice cold. I consider that a short term win until I can find a blend door for replacement. Feel free to hit me up with any questions or comments.