Front heat works fine but rear heat only blows cold air on 2006 GMC Yukon Denali

All of the rear control settings (fan, vents, etc.) work fine but it will only blow cold air. The front heat works fine.

Asked by for the 2006 GMC Yukon Denali
needs a proper bleeding, make sure there is no air lock. last thing your back pipes may be blocked.
hope this helps.
2 more answers
rear actulator
Had the same problem and because my car was under warranty at the time had it fixed. A few weeks later when I went to actually use the heat in the back of the truck it was still blowing cold air. What the dealer put in was the wrong part and told me it needed a new heating element and wanted to charge me over $600. I told them they never fixed it. They basically just guessed what was wrong and never reteseted it...yes, believe it. It finally works correctly with new element and after discussions back and forth they only charged me a deductibke because my warranty had expired.