I own a 2001 Mercury Sable which for the past 2 years has an overheating problem. I can run all around the texas heat with no problems until I turn on the Air Conditioner. I drive to work with it on and the temp never raises above center. During the afternoon in the heat of the day when I turn it on it start a slow climb. The minute I turn off the AC it drops back to center. I have had the dealer look at it and sitting in the shop it never overheats. They charged me for a flush and fill and system check anyway but driving home it began to climb again. I dont believe it to be a thermostat problem since it only overheats with the ac on. I do hear the fans kick on as the heat climbs so I dont think it would be that. Any help is appreciated.