OEM Lennox Control Transformer 24V — 99K12

The genuine OEM Lennox 99K12 transformer steps down incoming line voltage to the 24-volt control power that runs your thermostat, gas valve, relays, and control board. It is a critical component in Lennox furnaces and air handlers — without steady 24V output, the low-voltage control circuit simply cannot operate. This factory part is engineered to match the exact VA rating and mounting footprint of your Lennox equipment.

Common failure symptoms: a system that is completely unresponsive, a blank or dead thermostat, blown low-voltage fuses, tripped control boards, or a faint burning smell from an overheated winding. Transformers commonly fail from a shorted thermostat wire, a stuck contactor, or age-related insulation breakdown.

Why OEM matters: the Lennox 99K12 is built to the precise primary and secondary voltage, VA capacity, and terminal configuration your system's control board expects. An undersized or mismatched aftermarket transformer can overheat, deliver unstable voltage, or fail prematurely. Choosing the genuine Lennox part ensures reliable control power, proper fit, and full compatibility with your equipment.