What is the odor coming from your vehicle air conditioner?

Condensation forms on cool evaporator fins and tubes and collects in the pan. Inlet air brings along contaminants like dirt, pollen and plant and animal debris, some of which is deposited on the wet fins and in the pan. Additionally, if a system spends much time in re-circ mode, it also gathers matter like pet hair and nicotine and tars from cigarette smoke. Another cause could be leaking evaporators allowing oil to coat the fins. Certain evaporators, housings and pans are more prone to accumulating these contaminants than others. Armed with the nourishment (contaminants) listed above, the warm, moist, dark, environs of the housing encourage beasties (microorganisms, mold, mildew, fungi, bacteria, etc.) to form and multiply. Being alive and growing means they produce gas. This gas, a volatile organic compound, IS the problem: its moldy odor stinks. I suggest you do a Google Search or contact your local parts store for products to help eliminate the mold. In the mean time try not using the A/C and running the fan on high in the non-recirculate mode. This will help to dry out the system and help kill some of the mold. Also make sure the A/C condensor drain line is clear.