Air Conditioner

In most cases this is due to a low refrigerant level. If this is the case then there is a leak in the system and it's important to repair the leak before adding any more refrigerant. Other issues could be a slipping belt, slipping compressor clutch, or a partially blocked expansion valve or A/C line.

I agree with Rdude 135. You have to either put dye in the system or have a A/C leak detector. either way you will have to top off the system. Most likely you have a evaporator leak.