OEM Lennox Heat Pump Defrost Control Board — 33G9501

The genuine OEM Lennox 33G9501 defrost control board manages the defrost cycle on your Lennox heat pump. Using timer and temperature-sensor inputs, it decides when to reverse the refrigerant flow to melt frost from the outdoor coil, energizes the reversing valve and auxiliary heat, and returns the system to heating — all while protecting the compressor from short-cycling. It is built to Lennox specifications for a direct, reliable fit.

Common failure symptoms: When the 33G9501 fails, the outdoor unit may ice over and never clear, run excessively long or unnecessary defrost cycles, blow cold air indoors, or fail to switch the reversing valve. Weak heating performance, tripped defrost sensors, or a coil buried in frost are classic signs the defrost board needs replacement.

Why OEM matters: Defrost logic and timing vary by heat pump design, and a generic board can mistime cycles, waste energy, or leave the coil frozen. The factory-original 33G9501 provides the correct sensor thresholds, cycle timing, and terminal layout for your Lennox heat pump — preserving efficient defrost operation, compressor protection, and rated heating capacity.