Did someone clean your airconditioning system. Maybe its too dirty already that is why it cannot perform well. Its part of the maintainace of a car aircon. There is a periodic service. Anyway, supposed you someone clean it and still you don't get satisfy with its coolness, look for a leak in the freon gas. check the hoses, compressor, condenser evaporator for leaks. This causes weak aircon. Lastly, check the auxilliary fan of the condenser, it might not working fine. this causes the airconditioning system under high pressure which makes the coldness of your aircon lessen