Blend Door questions

Hello Everyone;I have a friend with a 1999 Dodge Ram 2500.The dealer said this truck has one electrical blend door and its above the transmission hump against the floor.The original motor ran all the time because the coupler link broke in to.He glued it back together and the motor runs all the time on hot and cold. The motor will not stop running and the coupler is still in in one piece now.So we ordered a new blend door motor from Chrysler.The old one had 3 pins at the plug in.The new one has 4 pins.He can install the new motor and turn the control to cold and the motor will stop and then turn the control to hot and the motor continues to run.Can someone please explain what limits the blend door motor and why did the original coupler break?

Are you sure this is the correct motor?