Spring start-up: inspect and clean condenser coils; verify fan motors, contractors, capacitors, and crankcase heaters; check refrigerant charge (pressures, superheat, subcooling); and test cooling operation under load. Fall changeover: transition systems to heating mode; inspect and test gas furnaces, heat pumps, electric heat strips, and hydronic heat (burners, ignition, flue/venting, heat exchangers, safeties, and reversing valves as applicable).