OEM Lennox Time Delay Circuit Board — 78K59

The genuine OEM Lennox 78K59 time delay circuit board manages the sequencing and timing logic of your Lennox furnace or air handler. It governs the fan-on and fan-off delays that let the heat exchanger warm up before the blower engages and continue circulating residual heat after the burners shut off — maximizing comfort, efficiency, and equipment life. As the timing brain of the blower cycle, it coordinates safe, orderly startup and shutdown on every call for heat.

Common failure symptoms: a blower that runs constantly or never starts, incorrect or missing fan-on/fan-off delays, cold-air blows at the start of a cycle, short cycling, intermittent no-heat conditions, or visible scorching, corrosion, and burnt relays on the board itself.

Why OEM matters: the Lennox 78K59 is programmed with the exact delay timings and relay logic your specific model was engineered around. Aftermarket boards often use different timing profiles or relay ratings that cause comfort complaints, efficiency loss, or premature component wear. Installing the factory board guarantees correct sequencing, reliable operation, and full compatibility with your Lennox system while protecting your warranty.