A/C Blows Hot and Cold Air on 2004 GMC Yukon

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When air conditioner is turned on it blows cold air on passenger side and hot air on driver's side. Previously, after turning off ignition and restarting the A/c would work fine. Now, it won't correct itself...blows very hot on driver's side and cold on passenger side. How can this be fixed and how expensive? Thanks.
(1) Answer
I hand the same problem, i had hot air in front and cold in the back.

remove the black plastic cover located right below your dash, covering the climate air vents .Locate the . . . I think the part name is call the Modedooractuator.This piece is made of plastic and had a electric connector attach. Well , I remove it and notice this vent door inside this part was not fully close so I clean it. , I spray a little lubricate and re-install it, Its been about 4 years and I never had that problem since. You may want to Google this" Moderdooractator"