2004 Mercury Sable Overheats when the A/C is turned on.

I have a 2004 Mercury Sable. It is my work car and I love this car. It has just started to overheat when I turn the A/C on. The coolant is fine has about 10,000 miles since last flush, and is full. The fans turn on. I do not see any signs of a coolant leak.

If I drive with out the A/C on the gauge stays dead center - no overheating. As soon as I turn on the A/C whether driving on city streets or highway it will over heat.

Not sure if it matters but it has the automatic climate control.

Thanks for any help.