If your car's air conditioning is giving off a less-than-pleasant odor, you could have a problem. Though the issue is relatively minor compared to other types of car A/C problems, it is still wise to drive to your trusted mechanic and have him take a quick look.
A car's air conditioning system has six main components: the compressor, condenser, evaporator, expansion valve, receiver and refrigerant unit. The compressor powers on when you turn on the air conditioner, and it pushes hot pressurized vapor out from the refrigerant unit. It routes the vapor to the condenser, where it converts to a liquid. The liquid transfers to a receiver unit, which removes moisture from the refrigerant and transfers it to the expansion valve. As the name suggests, the valve expands the liquid and transforms it to a vapor again. The vapor moves into the evaporator, which is what cools the passenger compartment. This process sounds long, but it usually happens in a matter of minutes.
In some cases, a foul smell from the air conditioning vents of your car could mean the remains of a small animal, like a bird or raccoon, are under the hood of the car. Lift the hood or slide yourself beneath the undercarriage with a flashlight to inspect the area. This is definitely not a pleasant discovery to make, but it is a common source of bad smell. You can either remove the animal yourself or have your mechanic handle the task.
In some cases, moisture trapped inside the condenser or evaporator of the car is the reason for the smell. Over time, the moisture turns into mildew and gives off an unpleasant odor. You may be able to fix the problem by letting the fan (not the A/C) run for a few minutes after running the air conditioner.
Sometimes you may confuse an A/C issue with a general problem in the car's engine. The coolant in the car's radiator unit is sometimes the culprit if you have a strong, unpleasant smell emanating from your vents. The coolant may have toxic ingredients, and if it starts to leak from a hose or radiator cap, it can cause odor. In this case, either your mechanic has to check for leaks or you can try a different type of coolant.
