Method for controlling an HVAC ventilation fan in heating or cooling mode and varying the fan-off time delay as a function of heat source or cool source operational time. Method for increasing heater ventilation fan speed from the low speed used for heating to the high speed used for cooling. Method for maintaining the heat pump reversing valve signal at the same position throughout the cool or heat source operational and extended variable fan-off time delay. Method for closing economizer dampers at the end of the cool or heat source operational time while continuing to operate the ventilation fan for an extended variable fan-off time delay.