OEM Lennox Transformer — 78H55

The genuine OEM Lennox 78H55 transformer steps down incoming line voltage (typically 120V or 240V) to the 24V low-voltage power that runs your thermostat, control board, gas valve, and relays. It is a foundational component in Lennox furnaces and air handlers — without it, the entire control circuit goes dead. This is a direct factory replacement engineered to match the exact VA rating, mounting footprint, and wiring configuration of your Lennox system.

Common failure symptoms: a completely unresponsive thermostat, a system that won't power on, blown low-voltage fuses, a burning smell near the control board, or intermittent operation. A shorted or overloaded transformer often fails after a control-side short, so inspect downstream wiring before installing the new unit.

Why OEM matters: Lennox control boards and safety circuits are calibrated to precise voltage tolerances. An OEM 78H55 delivers the correct VA capacity and stable output that generic transformers can't guarantee, protecting sensitive electronics and preserving your equipment warranty. Choosing the factory part ensures reliable ignition, proper relay actuation, and a clean bolt-in fit every time.