As an auto mechanic, you would be exposed to dust, fumes (including diesel fumes) & gases, and a variety of chemicals, often referred to as Volatile Organic Chemicals (VOC), but almost certainly, not to asbestos. There is one report of an increased incidence of breast cancer in women exposed to VOC’s, but this has not been confirmed.
Being an auto mechanic poses very little risk from these inhaled materials, if a person has normal lungs to begin with. A person who already has an underlying chronic lung disease, such as asthma, cystic fibrosis, COPD would be wise to avoid any such occupational exposures, altogether.
Air conditioning and refrigeration repair can be hazardous. Freon and other such materials used in refrigeration systems decompose on heating and produce substances that are highly irritating to the airways.
Any of these occupational materials are much more hazardous if an individual also smokes cigarettes.
For further information on hazardous occupational exposures, I suggest that you go to the OSHA website at www.osha.gov