A poorly performing car air conditioning system can cause a build up of fungus, bacteria and other microbes growing inside the evaporator core, causing a smell, sometimes an allergic reaction and can lead to legionnaires disease.
Have your car air con system serviced every 18 months. It will recommend that in your car manufacturers service guide, yet when your car is serviced, your A/C system is never serviced. It's an extra, chargeable item, but vital to have done.
A typical main dealer car air conditioning service will cost you at least £100, plus you take the car to them.
A poor aircon system can increase your fuel costs as the air conditioning pump needs to work harder.