Thanks for all of your kind suggestions, Gentlemen. I got AC technician checked the Freon level for me and found out it is low. After the recharge, AC is functioining normally now. Your kind professional help is greatly appreciated. One more question is regarding ATF (Auto Transmission Fluid) change. I am the 2nd owner of 97 E420. The car has 103,000 miles. Three MB dealers suggested me to machine flush + drain and change filter and pan gasket. One MB dealer told me not to touch it because the old fluid already broken down and difficult to be drained off. If I machine flush it and refill with new fluid, it would cause more break down and gear shifting problem including the potential leaking issue. Your kind technical suggestions to clarify my confusion are really appareciated.