Hi Rizal,
The air conditioning works by blowing air through the condensor that's mounted in front of the radiator, which takes away the heat that's being exchanged for cold inside the evaporator. If not enough air is going through the condensor, then it's not going to take away the heat and the car won't blow cold air.
When the car is moving, there's plenty of air going through the radiator, but when it's stopped it depends on the radiator fan to move air through. If that fan has failed you'll get the exact symptoms you're seeing. Open up the hood and verify that the radiator fan is running when the car is stopped and idling with the A/C on. If not, you'll have to try and diagnose whether it's a failed fan motor or a wiring problem, which could include wires, connectors or fuses. Here's what you're looking for.
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