Abstract
Exhalation of unpleasant odors from the car´s air conditioning system leads to
customer complaints. Analysis showed that hot and humid (tropical) weather conditions lead
to a significant increased number of odor complaints and that the problem increases with the
mileage of the car. With questionnaires and market research, five different types of odor
impression were defined. Intense chemical and microbiological analysis of complaint cars, as
well as tests on bench were done to identify the reasons for HVAC smell.
The majority of odor complaints is caused by the settlement of bacteria on the fins of the
evaporator and the high amount of condense water in the evaporator core. The adhesion of
odors and gaseous pollutants from the interior, as well as the inherent smell of the evaporator
cause further complaints. Possible passive countermeasures are improved HVAC unit designs
with permanent fresh- and recirculated air filtration to prevent a contamination with bacteria
and pollutants. Active countermeasures will be the development of improved evaporators and
new coatings, to improve the water drain and to prevent the growth of bacteria with biocides.
The combination of active and passive countermeasures will be the best working solution.
For already sold cars, aftersales service offers a variety of cleaning agents to disinfect the
components of the HVAC unit. Experience also showed that especially in hot and humid
countries, a regular cleaning is often necessary to suppress the forming of new odors.
BMW expects clearly improvements in the design of the HVAC units to prevent odor
problems in future cars.
Keywords: Air Conditioning, Climatic Conditions, Odor, Adhesive Smell, Metabolites
of Bacteria.