Repair or replace defective parts in units and equipment and their controls, including thermostats, automatic switches, fan controls, log switches, damper motors, louvers, relays, filters, controls, belts, compressors, heat exchangers, high limit controls, pressure controls, safety valves, and automatic gas valves. Requires activities involving being around moving machinery, exposure to marked changes in temperature and humidity, and exposure to dust, fumes, and gases.