i've got a friends heat pump that doesn't defrost every day, only like every other day and the temperature drops to approx. 25 degrees. He said the condenser fan motor is running when he looks at the unit in the mornings. i did replace the defrost control, thermostat and sensor since the unit is 10 years old. this board doesn't have any adjustable times on the board. i think the new board is bad but they say highly unlikely. the refrigerant charge is good.