HVAC: Perform maintenance and diagnostic repair on interior and roof-top heating and cooling systems, including but not limited to boilers, hot water heaters, heat pumps, rooftop units, energy recovery units, cooling towers, variable frequency drives, geothermal systems, chillers, pneumatic controls, and direct digital controls. Perform scheduled preventive maintenance and service on HVAC system equipment, such as changing filters and belts; lubrication of motors, pump and fan bearings; washing of coils; evaluating pressures; running diagnostic tests; ensuring proper voltages and amps; calibrating and adjusting direct digital control equipment; testing and replacing treatment chemicals; and similar activities.