Conduct and follow regular preventive maintenance schedules and inspections on refrigeration units, isolated heating and ventilating units, including boilers, gas and electrically operated air-conditioning equipment, and make necessary adjustments or repairs, service and repair evaporative coolers. Inspect, diagnose, repair, modify and install mechanical equipment including refrigeration and air conditioning compressors, receivers, condensers, forced air converter units, pumps, automatic and hand valves, expansion valves, and capillary tubes.