Please help, I have a 2007 ford five hundred with 60,000 miles, out of warranty. I am having a/c problems. As long as the engine is revving at about 2000 rpm or the car is being driven the a/c cools fine. At idle for any length of time the a/c starts to warm up and gets progressively warmer the longer you sit. To the point it seems it doesnt cool anymore. It warms instantly so I dont think something is froze up, and when I drive it instantly cools down. I have recently had the expansion valve replaced and the system charged, this did not help. The shop were I took it to is aware it did not work, I just have to wait a day or two for the weather to warm back up again and have them take another look at it. They seem just as puzzeled as I am. Any ideas?