Apologies VNAVSPD - sort of a terminology/technology gotcha the Gasper fan is. (old terminology, that is)
The Gasper fan blows air through the overhead vents (gaspers) even with packs off and also provided adequate and even temp airflow during limited pack operation.
Now we have a recirculating fan that more or less does the same thing - except that it provides airflow to the ceiling outlets, sidewalls and overhead vents thanks to a lighter, lower amperage,yet more powerful motor.
If I recall correctly, the purpose of the gasper fan on the 742 was to provide additional cool air flow (from the cold air plenum) to the passenger outlets during hot weather operations, while the recirculating fans could blow hot or cold.