Heating, ventilation and air conditioning technicians work on heating, ventilation, and cooling systems that control the temperature and air quality in buildings. HVAC technicians work in residential homes, schools, hospitals, office buildings, or factories etc. Their worksites may be very hot or cold because the heating and cooling systems they must repair may not be working, and because some parts of these systems are located outdoors. Irregular hours and working in cramped spaces are common.