Air Condition Problem on 2002 Mercedes-Benz C240

I turn my car on in the summer and leave it for about tem min for the Air Condition to cool the car from inside, but after 10 min it's still hot, untill I drive the car in the Air Condition start working and I start feel the cool Air coming out, what is the problem?

Asked by for the 2002 Mercedes-Benz C240