Performs preventive maintenance, overhauls and/or repairs, heating, ventilating, air conditioning and refrigeration equipment, including but not limited to gas-fired furnaces, and gas-fired hot water boilers, chillers, condensing units, freezers, packaged units and related controls and equipment. Determines methods and sequences used to install, overhaul, service and maintain all types of air conditioning, heating, refrigeration, ventilating and associated equipment as related to air conditioning and refrigeration systems.