What would cause my air conditioner in my 2007 Crown Victoria not to change back from heat to air conditioner? How to fix it?

blend door actuator. Very common problem with those cars. Hard to change. You have to take the whole dash board out sometimes you can remove glove box and tear down everything on passenger side and reach in. It is located on top of air box in center of vehicle. One plug 4 mounting screws. I suggest get it from dealer since I have had several problems getting the correct one from parts houses and it will fry the head unit if it is not the correct one. They look identical so you wont know it is the wrong one until you have fried the computer. looks like this http://www.stockwiseauto.com/product_info.php/products_id/242263/fit _id/12197/Year/2007/Make/Ford/Model/Crown%20Victoria/source/goo gleps?gclid=CIq-tf6y8LoCFVFk7Aody00AnQ

Very common problem and quite a PITA to address. mike198420 is on the money. Either Flat-Rate it through the Glove box (don't break the top of the Plenum) or pull the dash.