Help with my 1997 Ford Taurus?

[SAM]

I have a 6 cylinder, 1997 automatic for taurus that will over heat when its idling, the heater dosnt blow hot air in the winter, and sometimes will have a small amount of odorless smoke come into the car when the air condition is on(happens very rarely and is very little amount of smoke almost looks like mist). i am concerned about it over heating when idling but to my surprise the tempeture goes down when the car is moving though. I do notice that the noise i would hear when the fan kicked on is no longer there and I dont know if I have to replace the fan or if it could be some type of sensor not telling it to turn on or a fuse. Anyone know what it could be and how i would go about finding out for sure then fixing it? any help would be useful. Thanks
I havnt seen or felt any damp spot inside the car at all. Is there any other ay to determne its the heater core? also why does the car over heat when idling but not when the car is in motion of its the heater core?