Heating, air conditioning, and refrigeration mechanics and installers—often referred to as HVAC technicians—work on heating, ventilation, cooling, and refrigeration systems that control the air quality in many types of buildings. They mostly work in residential homes, schools, hospitals, office buildings, or factories. Their worksites may be very hot or cold because the heating and cooling system they must repair is broken. Working in cramped spaces is common. Most work full time.