I have a 2011 Acadia. The AC went out and was the evap core. I replaced the evap core, charged the system, and everything was fine. Now, we want the heat to work, but the blend doors fro the front or stuck in the cold position. The mode actuator works fine and switches the air output to where ever I direct it to. The temp for both driver and passenger won't move. I have unscrewed both actuators and watched them electrically work. the blend door though, I can't get it to turn by hand. How do i get this unstuck? There is heat in the rear, and the heater core is hot as it should be. Just can't get the temp blend door to move so it won't change the air temp.