Before you change the temp, make sure you....
 

....turn the fan off. I just changed out my heat and a/c controls on the dash (PITA), because the hot cold slider had broken. MyGreenMax94 has a good photo here:http://forums.maxima.org/showthread.php?t=491440

After I installed the new controller, I found out why the old one failed. If you have the fan at a high setting and try to move the temp from hot to cold,there was a lot of stress on the slider, making it difficult to move. Once I turned off the fan it moved normally. If you follow this advice, you could possibly save yourself several hours of work ripping out the dash.